Difference between revisions of "Working with the C-CWEL data"

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''This page is an updated version of the [[Working with the C-WAYS data]] page, which was an update of the  [[Working with the BRCs]] page, which was an update of the [[Working with CG4+SA101]] page, which was an update of the [[Working with L1688]] page. '''This''' page was developed and updated specifically for the 2013 C-CWEL team visit.  Please note: '''NONE''' of these pages are meant to be used without applying your brain! They are NOT cookbooks!''
+
''This page is an updated version of the [[Working with the C-WAYS data]] page, which was an update of the  [[Working with the BRCs]] page, which was an update of the [[Working with CG4+SA101]] page, which was an update of the [[Working with L1688]] page. '''This''' page was developed and updated specifically for the 2013 C-CWEL team visit.   
 
 
This is presented as a linear progression, but chances are excellent that you will go back and redo different pieces of this at different stages of your work.
 
  
 +
'''Please note''': '''NONE''' of these pages are meant to be used without applying your brain! They are NOT cookbooks!''  This is presented as a linear progression because of the nature of this page, but we have already done some things "out of order", and moreover, chances are excellent that you will go back and redo different pieces of this at different stages of your work.
  
 
FOR REFERENCE: [[C-CWEL Bigger Picture and Goals]]
 
FOR REFERENCE: [[C-CWEL Bigger Picture and Goals]]
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<font color="red">(just for reference)</font>
 
<font color="red">(just for reference)</font>
  
*BRC 38 21:40:42 +58:16:12.8
+
BRC 38: 21:40:42 +58:16:12.8
  
 
And, we care about stuff within a ~20 arcmin radius of these positions. (which means 40 arcmin on a side if you are pulling a square rather than a cone.)
 
And, we care about stuff within a ~20 arcmin radius of these positions. (which means 40 arcmin on a side if you are pulling a square rather than a cone.)
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=Obtaining the data=
 
=Obtaining the data=
  
We have just one region we care about, so just one places to search on the sky. We need to get the relevant data from both WISE and Spitzer.
+
<font color="red">DONE</font>
 +
 
 +
We have just one region we care about, so just one place to search on the sky. We need to get the relevant data from both WISE and Spitzer.
  
 
''WISE'' -- [[How do I download data from WISE?]] has a simple walkthrough, with links to more tutorials. And, [http://irsa.ipac.caltech.edu/applications/wise/  Access the WISE archive directly here].  You will need to get images and catalogs, both, for a 20 arcmin radius from the center position of BRC 38.
 
''WISE'' -- [[How do I download data from WISE?]] has a simple walkthrough, with links to more tutorials. And, [http://irsa.ipac.caltech.edu/applications/wise/  Access the WISE archive directly here].  You will need to get images and catalogs, both, for a 20 arcmin radius from the center position of BRC 38.
  
''Spitzer'' -- [[How do I download data from Spitzer?]] has a wide variety of flavors of tutorials.  The [http://irsa.ipac.caltech.edu/data/SPITZER/docs/dataanalysistools/cookbook/6/#_Toc288477466 second formal chapter] of the professional astronomer's Data Reduction Cookbook ultimately comes from a 2010 NITARP project. I haven't developed one customized to your project. However, as you know, there will only be Spitzer data centered on BRC 38.  You will need to find the data, and download it.
+
''Spitzer'' -- [[How do I download data from Spitzer?]] has a wide variety of flavors of tutorials.  The [http://irsa.ipac.caltech.edu/data/SPITZER/docs/dataanalysistools/cookbook/6/#_Toc288477466 second formal chapter] of the professional astronomer's Data Reduction Cookbook ultimately comes from a 2010 NITARP project. I haven't developed one customized to your project. However, as you know, there will only be Spitzer data centered on BRC 38.  You will need to find the data, and download the files.
  
 
'''Big picture goal''': Get the data you need for this project. Get you comfortable enough to search for your own favorite target in WISE and Spitzer, understand what to do with the search results, and download data.  
 
'''Big picture goal''': Get the data you need for this project. Get you comfortable enough to search for your own favorite target in WISE and Spitzer, understand what to do with the search results, and download data.  
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#How do you download ''source lists'' from WISE, as opposed to images? The catalog will come with 2MASS matches already done, but you can also get catalogs from 2MASS this way; you will need this below.
 
#How do you download ''source lists'' from WISE, as opposed to images? The catalog will come with 2MASS matches already done, but you can also get catalogs from 2MASS this way; you will need this below.
  
=Getting data from other wavelengths =
+
=Investigating the mosaics =
 
 
You have already done most of this in your literature search and [[C-CWEL Resolution Worksheet |resolution worksheet]] this Spring. However, if you don't still have the images you found before on your laptop, you might as well go grab them again.
 
 
 
'''Big picture goal''': Understand how to use the various archives to find non-Spitzer data.
 
 
 
'''More specific shorter term goals''': Go get data for BRC 27 from POSS (images) and IRAS (images) and 2MASS (images and '''catalogs''') for comparison to our data. 
 
 
 
'''Relevant links''': [[How can I get data from other wavelengths to compare with infrared data from Spitzer?]]  and  [[Resolution]] 
 
 
 
'''Questions for you''':
 
#Figure out how to get images from at least POSS and IRAS. Get images covering about 20 arcminutes in radius from the center position so that they are easy to compare, but larger scale images might be useful to give a sense of context too. Watch your pixel scale! Start to look at these images in context of the WISE images. Between POSS and WISE, what is bright, and what is faint? Between IRAS and WISE, what breaks into pieces or dissolves into nebulosity when viewed at higher spatial resolution?
 
#Figure out how to get catalogs from 2MASS (not images per se!). You can do this via the WISE archive. The WISE catalogs come with some 2MASS matches, but the details of the matching process are sometimes a little obscure, so original 2MASS catalogs are also useful. Get catalogs covering about 20 arcminutes in radius from the center position. This will be a big file.
 
#BONUS: use the catalog trick to get Akari data in our region of interest.
 
  
=Making and investigating the mosaics =
+
<font color="red">DONE</font>
  
'''It is "real astronomy" to spend a lot of time staring at the mosaics and understanding what you are looking at. Don't dismiss this step as not "real astronomy" just because you are not making quantitative measurements.  This is time well-spent, and you should plan on investing some time doing this section.'''  
+
'''It is "real astronomy" to spend a lot of time staring at the mosaics and understanding what you are looking at. Don't dismiss this step as not "real astronomy" just because you are not making quantitative measurements.  This is time well-spent, and you should plan on investing some time doing this section.''' Some aspects of this were already discussed in the context of the Resolution worksheet.
  
For the WISE data, we can use the mosaics as provided by the WISE archive. BRC 38 happens to fall on a boundary between tiles as provided. For when we want to make a big mosaic (or a "pretty picture"), we can either use [http://skyview.gsfc.nasa.gov/cgi-bin/skvadvanced.pl Goddard's Skyview] to make mosaics, or [[Making Mosaics Using MONTAGE| MONTAGE]].
+
For the WISE data, we can use the mosaics as provided by the WISE archive. BRC 38 happens to fall on a boundary between tiles as provided. If you want in the future to make a big mosaic (or a "pretty picture"), we can either use [http://skyview.gsfc.nasa.gov/cgi-bin/skvadvanced.pl Goddard's Skyview] to make mosaics, or [[Making Mosaics Using MONTAGE| MONTAGE]].  We have mosaics that Xavier made us that are centered on BRC 38 (and I honestly don't know what software he used to generate them). Look on the DVD I gave the educators.
  
For Spitzer data, in the generic case for most targets, you can probably use the online mosaics that come as PBCD (Level 2) mosaics (or delivered products, if they exist for the region you want -- see "enhanced product search" in the SHA).  In this case, we can most likely get by just fine with the online mosaics.
+
For Spitzer data, in the generic case for most targets, you can probably use the online mosaics that come as PBCD (Level 2) mosaics (or delivered products, if they exist for the region you want -- see "enhanced product search" in the SHA).  In this case, we can probably get by just fine with the online mosaics.
  
 
'''Big picture goal''': Recognize at a glance what is an instrumental artifact and what is real. Understand what is seen at each WISE and Spitzer band and all the other archival bands.
 
'''Big picture goal''': Recognize at a glance what is an instrumental artifact and what is real. Understand what is seen at each WISE and Spitzer band and all the other archival bands.
  
'''More specific shorter term goals''': Understand what is part of the sky and what is an artifact (e.g., not part of the sky).  Understand what might need reprocessing. Recognize how the images differ among the BRCs, and among the various bands.  
+
'''More specific shorter term goals''': Understand what is part of the sky and what is an artifact (e.g., not part of the sky).  Recognize how the images differ among the various bands, and why.  
  
 
'''Relevant links''':   
 
'''Relevant links''':   
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*Possibly [[Making Mosaics Using MONTAGE]].  
 
*Possibly [[Making Mosaics Using MONTAGE]].  
 
*[http://skyview.gsfc.nasa.gov/cgi-bin/skvadvanced.pl Goddard's Skyview]
 
*[http://skyview.gsfc.nasa.gov/cgi-bin/skvadvanced.pl Goddard's Skyview]
*[[Resolution]] and associated [[C-WAYS Resolution Worksheet]].  
+
*[[Resolution]] and associated [[C-CWEL Resolution Worksheet]].  
 
*Why does it matter to know what is an artifact and what is not? [http://www.universetoday.com/86497/proof-bio-station-alpha-is-just-an-image-artifact/ So you don't get fooled by stuff like this.]  
 
*Why does it matter to know what is an artifact and what is not? [http://www.universetoday.com/86497/proof-bio-station-alpha-is-just-an-image-artifact/ So you don't get fooled by stuff like this.]  
 
*[[How can I make a color composite image using Spitzer and/or other data?]]
 
*[[How can I make a color composite image using Spitzer and/or other data?]]
 +
*[http://nitarp.ipac.caltech.edu/resource/8 ds9 NITARP Tutorial] (listed on that page, along with installation tips)
 +
*[http://hea-www.harvard.edu/RD/ds9/site/Download.html ds9 Download site]
  
 
'''Questions for you''':  
 
'''Questions for you''':  
#What is saturated? Are the same objects saturated in all bands? What are some other instrumental effects you can see?
+
#'''MOST IMPORTANT of these questions: Compare the mosaics across the bands. What changes? What stays the same? Why? (This is a DEEP question! See also next questions.)'''
#Notice the pixel scale. What is the real pixel scale of the original instrument (WISE, IRAC, MIPS)? What are the pixel scales of the images? Does that actually change the resolution? (for advanced folks - why did we do this?)
+
#How does the number of '''stars''' differ across the bands? Which band has the most stars? The fewest? (Bonus question: why?) The most '''nebulosity'''? The least? (Bonus question: why?) Are there more stars in the regions of nebulosity, or less? Why?  
#Compare the mosaics across the bands. What changes? What stays the same? Why? (This is a DEEP question! See also next questions.)
+
#What is saturated? Are the same objects saturated in all bands? What are some other instrumental effects you can see? [[Example Spitzer/MIPS image with substantial artifacts here]] if you want to train your eye, or see an extreme case. (Bonus: which way was the scan map 'painting' the sky?)
#How does the number of stars differ across the bands? Which band has the most stars? The fewest? (Bonus question: why?) The most nebulosity? The least? (Bonus question: why?) Are there more stars in the regions of nebulosity, or less? Why?  
+
#Notice the pixel scale. What is the real pixel scale of the original instrument (WISE, IRAC, MIPS)? What are the pixel scales of the images? Does that actually change the resolution? (for advanced folks - why did we do this?) (You may have already addressed these issues during the [[Resolution]] work earlier this year.)
#How big are any of the features in the image (nebulosity, galaxy, space between objects)? (What do I mean by big?) in pixels, arcseconds, parsecs, and/or light years? (Hint: you need to know how far away the thing is. If it helps, there are 3.26 light years in a parsec.)
 
 
#Make a three-color image.  What happens when you include a MIPS-24 or WISE-22 mosaic in as one of the three colors with shorter bands as the other two colors? (NB: this might be easiest within the same telescope, e.g., use just WISE bands or just Spitzer bands to make a 3-color image.) Do the stars match up? Does the resolution matter? Can you tell from just a glance at the three-color mosaic which stars are bright at 22 or 24 microns?   
 
#Make a three-color image.  What happens when you include a MIPS-24 or WISE-22 mosaic in as one of the three colors with shorter bands as the other two colors? (NB: this might be easiest within the same telescope, e.g., use just WISE bands or just Spitzer bands to make a 3-color image.) Do the stars match up? Does the resolution matter? Can you tell from just a glance at the three-color mosaic which stars are bright at 22 or 24 microns?   
#How much more detail do you see with Spitzer that was missed by WISE? or IRAS? How does the resolution and sensitivity vary?
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#How much more detail do you see with Spitzer that was missed by WISE? How do the resolution and sensitivity vary?
 +
#BONUS: How big are any of the features in the image (nebulosity, galaxy, space between objects)? (What do I mean by big?) in pixels, arcseconds, parsecs, and/or light years? (Hint: you need to know how far away the thing is. If it helps, there are 3.26 light years in a parsec.)
 +
 
 +
=Getting data from other wavelengths =
 +
 
 +
<font color="red">Mostly already done</font>
 +
 
 +
You have really already done most of this in your literature search and [[C-CWEL Resolution Worksheet |resolution worksheet]] this Spring. However, if you don't still have the images you found before on your laptop, you might as well go grab them again (or get my copies off the DVD I gave the educators). You want at the very least POSS and IRAS images.
 +
 
 +
'''Big picture goal''': Understand how to use the various archives to find non-Spitzer data.
 +
 
 +
'''More specific shorter term goals''': Go get data for BRC 27 from POSS (images) and 2MASS (images and '''catalogs''') for comparison to our data. 
 +
 
 +
'''Relevant links''':
 +
*[[How can I get data from other wavelengths to compare with infrared data from Spitzer?]] 
 +
*[http://irsa.ipac.caltech.edu/applications/wise/ WISE archive]
 +
*[http://sha.ipac.caltech.edu/applications/Spitzer/SHA/ SHA]
 +
*[[Resolution]] 
 +
 
 +
'''Questions for you''':
 +
#Figure out how to get '''images from at least POSS'''. (Bonus: 2MASS images too.) Get images covering about 20 arcminutes in radius from the center position so that they are easy to compare, but larger scale images might be useful to give a sense of context too. Watch your pixel scale! Start to look at these images in context of the WISE images. Between POSS and WISE, what is bright, and what is faint? (Bonus: compare 2MASS, POSS, and WISE.) (Still intrigued? Another Bonus: Get IRAS too. Between IRAS and WISE, what breaks into pieces or dissolves into nebulosity when viewed at higher spatial resolution?)
 +
#Even though I've already gotten these and matched them for you, it is worth spending a few minutes figuring out how to get '''catalogs''' from 2MASS (not images per se!) so that you don't have to depend heavily on me in the future. You can do this via the WISE archive. The WISE catalogs come with some 2MASS matches, but the details of the matching process are sometimes a little obscure, so original 2MASS catalogs are also useful. Get catalogs covering about 20 arcminutes in radius from the center position. This will be a big file.
 +
#BONUS: use the catalog trick to get Akari data in our region of interest.
  
 
=Previously identified sources=
 
=Previously identified sources=
  
You've already done the bulk of this prior to the visit, but you should look at images, and spot-check my matching! This is probably done more easily as part of the next step.
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<font color="red">Mostly already done</font>
 +
 
 +
You've already really done the majority of this prior to the visit, but this is where it kind of falls in the logical progression here. (I see the progression as : pick target, get images, get multiwavelength images, get numbers for the sources in the images first from the literature and where others have done it for us, then do more ourselves, then make plots, etc.) In the context specifically of bandmerging (later step), it's probably good to spot-check my matching! But this spot checking is probably done more easily as part of a later 'data tables' step, once you have facility with ds9 and its regions files.
  
'''Big picture goal''': Understand what has already been studied and what hasn't in the 3 regions we care about.
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'''Big picture goal''': Understand what has already been studied and what hasn't in the region we care about.
  
 
'''Relevant links''':  
 
'''Relevant links''':  
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*[[C-CWEL Journal Club]]  
 
*[[C-CWEL Journal Club]]  
  
 +
'''IMPORTANT''': when we are done weeding source lists as per the below, we will have to get into SIMBAD and search for each of our sources, just to get another handle on whether or not anyone has done anything on them before -- because some of our sources are beyond where the prior papers were working, and they just might be something else already identified in the literature.
  
'''IMPORTANT''': when we are done weeding source lists as per the below, we will have to get into SIMBAD and search for each of our sources, just to get another handle on whether or not anyone has done anything on them before -- because some of our sources are beyond where the prior papers were working, and they just might be something else in the literature.
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=Bandmerging the photometry=
  
=Starting to work with the data tables =
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<font color="red">Mostly already done - but PLEASE thoughtfully read this section!</font>
  
OK, fair warning, some math involved, and the start of working with spreadsheets!
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This section could logically go elsewhere in this logical progression, but I think of bandmerging as having two parts -- combining the data from the literature, but also (later) combining data we have measured. Since I've basically done it for you, let's just keep this step here. This step is an explicit step in the journal articles we read.
  
'''Big picture goal''': Learn how to manipulate data tables.  
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'''Big picture goal''': Create a master catalog where there is one line per unique object that contains the measurements at all wavelengths and other relevant information all collected on same line. Understand what this process is, since I've already done most of it for you.  You need this catalog in order to make color-color and color-magnitude diagrams, and make SEDs.
  
'''More specific shorter term goals''': Understand how to import plain text tables into Excel (or another spreadsheet of your choice). Really look at the files as retrieved from the WISE archive and look at files as sent by Xavier and determine the relevant information out of these catalogs.
 
 
 
 
'''Relevant links''':  
 
'''Relevant links''':  
*[http://www.youtube.com/watch?v=nCJ3ctOGvNk YouTube video] on what tbl files are, how to access them, and specifically how to import tbl files into xls. (10min) 
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*[[Bandmerging]] definition with BRC 38 used as an example.
  
'''Questions for you''':
+
For future reference: The WISE data come out of the WISE archive already matched to 2MASS, so generally you don't have to do that. If you pull already reduced data from Spitzer for any given target, you will also most likely have quite a few objects bandmerged already.  
#We already have good coordinates from each paper for BRC 38. I matched them all; copies of these files are on the DVD and they should import cleanly into xls, but be careful about the limits (see below).  Spot check a few. Did I match them correctly? Which ones are the same between papers and which are new to just one paper?
 
##CAUTION 1: Some of the literature reported whole data tables, and some just reported the YSOs. So there are files with everything in the literature (long) and files with just the things someone in the literature tagged as YSOs. The files you want are the ones that are just the ones someone in the literature tagged as YSOs.
 
  
STOPPED SERIOUSLY UPDATING HERE. BE SURE DOCUMENTATION IN FILES THIS TIME.
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'''Important notes:''' In this specific case, I've done the merging for you, BUT...:
 +
*There are four objects that appear in the Choudhury data tables without coordinates, and I cannot locate coordinates for them. I wrote the author, but never heard back. Turns out that the T2 flux densities are also .. off. I can't tell what units they are in, except that they are definitely NOT the units as indicated in the table. More on this flux thing below. But for now I've been forced to just drop the objects without coordinates from our master catalog.
 +
*Akari data really does just have one source in this region that we might care about (18 over whole region but only 1 tagged before or now as YSO candidate), and Nakano already identified it. It's merged into my db but would mean 4 more columns in your Excel catalog for very little gain, so haven't given it to you.
 +
*IPHAS data release 2 still not out; the data that were mailed to us by Barentsen do not cover the entire area. Unfortunately, it's missing coverage in the south, the region where we are most likely to have YSOs that are optically detectable. We will work with what we can and watch for the IPHAS data when fully released.
 +
*Nakano's coordinates are .. not as good as I would have hoped. However, they list the 2MASS match, so I took the 2MASS name and decoded coordinates from that, then went forward with the merging process.
 +
*Xavier's new WISE color selection routines are far more restrictive than they were a year ago, and as such they omit a lot of the 'garbage' that last year's group had to still cope with. We therefore have a much shorter list than we might have had otherwise! Xavier's old classification scheme was more lenient, but it is possible that the new version discards real YSOs along with all the junk. I've retained the old classification scheme in case we whiz through the new ones and want more to chew on.
 +
*I get that there are between 20 and 50 objects that potentially have Spitzer data, including those already listed in the literature with one or more Spitzer bands. I did some quick-and-dirty automatic photometry. (This was how I discovered that the Choudhury T2 flux densities were just ..wrong. I match their T1 flux densities pretty well, but not their T2.) '''There is absolutely no guarantee that what I did is right''', especially since I did it 'blind', e.g., just trusting that the computer did it right, not checking to see if the answers were sensible (except via a bulk comparison to literature photometry values).
  
##CAUTION 2, AND THIS ONE'S A BIGGIE: '''This file has a mixture of detections and limits, measurements and errors, flux densities and magnitudes (with two different definitions of the latter!).''' The UBVRI are all Vega mags, no limits, and only some have errors. The Sloan r and i bands do have some limits, and these are AB mags. The JHK are all Vega mags, and some have limits. The IRAC and MIPS data are all in FLUX DENSITIES (uJy), and often have limits.  Just to add to the confusion (sorry!!!) the limits for this entire file are ALL IN FLUX SPACE, e.g., the sloan r mag for 07040072-1123234 is a limit, listed as 20.60, with a < (less than) sign; what this really means is "the true value of this object in this band is somewhere fainter than this value." For mags, this should be a GREATER number. So I just screwed up, but since I already burned all the DVDs, it's probably easier to explain it than fix it at this point.
+
=Data Tables, part 1=
#For each of the known objects, you have the RA/Dec - what is the easiest way to find the objects in the images you obtained above? (Hint: you want a ds9 regions file: [[file:ic1396knownysos.reg.txt]])  Take notes on any that look like the photometry may be corrupted or that you can easily dismiss as galaxies or other contaminants now that you are looking at better and/or different data than they had before.
 
#Look at the files from WISE and from Xavier. The files from WISE are better documented in the top of the file than mine are; Xavier's files have documentation in a separate file.  How is the information presented in the WISE catalogs and Xavier's catalogs the same/different? What information do we need?
 
#How do you figure out which ones have bad photometry according to the data quality flags?
 
#For each of the known YSOs, you have the RA/Dec - find the same objects in the WISE ''catalog''. Which objects are the matches? What constitutes a 'match'? Are there any with no matches?
 
Now, start to pull together stuff from this step plus those above. Here are plots (click to get a big one) of the spatial distribution of sources in all three regions we care about, with the symbols as defined in the plots (black dot = object in catalog, meaning WISE+literature data+my Spitzer catalog from last year's group; red circle = identified in the literature as a YSO; blue x = identified by Xavier's automatic code as likely clump of nebulosity; green diamond = identified by Xavier's automatic code as possible YSO; yellow diamond = IRAC data available in the catalog). Why are there some regions where WISE sources are missing? Why are the Spitzer sources where they are? (Is this all the Spitzer sources that are possible, or not? Why?) Why is there a patch of black in BRC 38 (hint: Beltran et al.)?
 
[[image:brc38where.png]]
 
  
 +
<font color="red">Essentially DONE</font> - assuming everyone have xls versions of the full and/or the 'interesting' catalogs...
  
[[file:datatableshelpjul2012.png|thumb]]
+
Hopefully, you already have developed some of these skills via [[C-CWEL Excel Practice]]. If not, this is the time to learn!
'''Updates added July 2012''':
 
*OK. Here was the leading edge of the confusion on source lists. The version from the DVD and the version that I posted on my personal website are a little different, with the latter (more recent) one being better to use. Most of the caveats above still apply.
 
*On the right is an attempted copy of the stuff I was writing which seemed to help better explain the relationship between these source lists and the questions.
 
  
'''Updates added 19 July 2012''':
+
'''Big picture goal''': Learn how to manipulate data tables. Look at the data tables to identify what you need. Start to cope with source list proliferation.  
One of my (Luisa's) action items was to look into the 'holes' in the spatial distribution of sources in BRC 27. I overlaid the full wise catalog on the WISE mosaics from Xavier. Of the three images here, there are two that have the whole catalog overplotted -- one is w1 and the other is w4; look at the header of the window in the screen snapshot to see which is which. The third has yellow squares too; see below for that.
 
  
<gallery widths="100px" heights="100px" perrow="3">
+
'''More specific shorter term goals''': Understand how to import plain text tables into Excel (or another spreadsheet of your choice). Really look at the files as retrieved from the WISE archive and look at files as sent by Xavier and determine the relevant information out of these catalogs. Keep track of which files are which.
file:wisecatonwise1.png
+
 
file:wisecatonwise4.png
+
'''Relevant links''':
file:wisecat+knownonwise1.png
+
*[http://www.youtube.com/watch?v=nCJ3ctOGvNk YouTube video] on what tbl files are, how to access them, and specifically how to import tbl files into xls. (10min) 
</gallery>
+
 
 +
Note that many data tables come with many, many, many lines (like more than 100) at the top explaining what the contents of the file are. These are useful for keeping with the file (like a FITS header is useful to keep with the image), but when reading it into Excel, you may wish to delete all but a note to yourself about what the file is, and the headers of the data columns themselves.
  
things to note:
+
'''Tasks and Questions for you''':
 +
#You should have a WISE catalog, either from your earlier download or the DVD. Load that puppy into Excel. Cope with the long header - scan it, keep it elsewhere, but you may not want to read it in to your Excel copy. What information do we need? How do you figure out which ones have bad photometry?
 +
#You should have a copy of Xavier's catalog with classifications on the DVD. Load that into another Excel worksheet or file. This one has a lot less documentation within the catalog; its documentation is a separate file, and you will need to consult this to decrypt which sources are YSO candidates and which are not. Figure out how to do this. There may be some utility in keeping the codes (rather than global search and replace).
 +
#Are these two files in the same order? (Did you change the order during the prior 'decryption' step? I did!) How could you find out, and fix this if necessary? Do they contain the same number of sources? Can you just copy the classification column out of Xavier's catalog into the WISE catalog? You need to tie Xavier's class to the WISE object, because in the next step, you will need a way of identifying the YSO candidates in plots.  Save this file as its own Excel file.
 +
#We already have good coordinates from each paper for BRC 38. I bandmerged all these catalogs for you; copies of these files are on the DVD and they should import cleanly into xls, but be careful about the limits (see below). 
 +
##CAUTION 1: Some of the literature reported whole data tables, and some just reported the YSOs. So there are files from me with everything in the literature (long) and files with just the things someone in the literature tagged as YSOs (short). There are also files from me with just the 'interesting' ones (meaning the literature-identified plus the new Xavier-identified). Because the file of all the 'interesting' sources has a column indicating whether the source is there because it is previously known ("PrevKn") or is in the list because it seems to have a WISE IR excess ("WISEIRx"), you can tell from that column in the 'interesting' files which sources are solely literature ("PrevKn") and which are literature but also seem independently to have an IR excess ("PrevKn+WISEIRx"). The sources you want to work with (for now) are the ones that someone in the literature tagged as YSOs. So, you can use EITHER the 'interesting' file OR the 'justlitysos' files. '''TO SAVE YOU WORK DOWNSTREAM, SUGGEST YOU LOAD 'INTERESTING' FILE.''' Save this as its own Excel file or worksheet, separate (tab or file) from the previous step.
 +
##CAUTION 2, AND THIS ONE'S A BIGGIE: '''These catalog files generally have a mixture of detections and limits, measurements and errors, flux densities and magnitudes.''' You will need to be careful in importing this into Excel. The UBVRIriHalphaJHK are all Vega mags, some have errors and some have limits. The IRAC and MIPS data are all in FLUX DENSITIES (uJy), and often have limits. 
  
we did a cone search on the wise catalog, and xavier made a square mosaic. so we 'lose' the corners. which is fine; we have a ton of other things to worry about with the objects we have.
 
  
there are far more sources seen at w1 that w4 (and you should know why by now!) :) most of the red circles are nicely on sources seen in w1; there are far fewer sources in the w4 image.
+
=Making color-color and color-magnitude plots=
  
if you draw a virtual line across the circle of sources from "11:00" to "4:00", the surface density of sources (e.g., how many sources there are on the screen per chunk of screen) is much higher on the lower left than on the upper right. if you look at the w1 image, you can see that this is for the most part consistent with what you actually see. at "12:00", i really don't see any sources (or many sources) in the black in between sources. it's even doing a pretty good job finding sources on top of the nebulous regions in the image, though some of them are likely to be false sources created by the computer doing the source detection 'seeing' ridges of nebulosity as instead sources.
+
<font color="red">Nearly done - need to make/compare CMDs/CCDs</font>
  
but the bottom middle is more of a problem. there is a bright source and nebulosity there. and i can see taht it caught a lot of the sources there. but there are a lot of legitimate sources, some reasonably bright, in those holes of "no catalog sources".
+
OK, fair warning, some math involved, and the start of ''programming'' spreadsheets!
  
THIS MEANS that if there are new legitimate YSOs here, we will not find them because they are not in the catalog. fortunately, not many of them are very bright, otherwise i would be worried. fainter means more likely to be xgal.
+
'''Big picture goal''': Understand what plots to make. Understand the basic idea of using them to pick out certain objects.
  
THIS ALSO MEANS that if any of our known objects fall in this region, they will appear to not have WISE detections when instead they actually should.
+
'''More specific shorter term goals''': Make some color-color and color-mag plots using the complete WISE catalog imported into Excel in the last step. At the very least, make a plot of the entire distribution and highlight the YSO candidates from Xavier.  
  
So, i plotted up everything on W1 - red circles is still the wise catalog, and now yellow boxes are the catalog of known YSOs.
+
'''Relevant links''':
 +
*[[Color-Magnitude and Color-Color plots]]
 +
*[[Gutermuth color selection]] - mostly currently Gutermuth color selection; includes analogy with M&Ms. Koenig color selection is similar in concept but uses different bands.
 +
*[[Finding cluster members]]
 +
*[[Color-color plot ideas]]
 +
*Also see slides from my set of talks on Monday.
  
there are several yellow boxes that are just outside of our 20 arcmin radius region of interest; i think it's ok to drop those off our list of things to think about.
+
'''Tasks and Questions for you''':
 +
#To do these next steps, you need a catalog that merges the WISE catalog, the 2MASS catalog, and the catalog from Xavier. If you did all the steps in the prior task, you have this now; I also have a copy of this for you on the DVD.
 +
#Start from the complete WISE catalog. Pick at least one color-color or color-magnitude plot to make (Suggestion: W1-W2 vs W3-W4, K vs. W1-W4 plot, or a W1 vs. W1-W4 plot).  Figure out a way to ignore the "no data" flags (exactly what they are depends on which file you are starting from - they could be 'null' or they could be '-9'). Does the photometry seem ok? Identify the regions where you expect to find the plain stars and the IR excess objects. 
 +
#Which objects are selected by Xavier's method as YSO candidates? Overplot them '''on the same plot''' as above with a different color and/or shape symbol. You may wish to try drawing the line segments on the plot too.
 +
#Bonus - read in one of my catalogs from the DVD that has literature sources indicated (e.g, the 'interesting' file loaded into Excel in the last step). Overplot these on the same plot, with a different color and/or shape symbol. Are the literature sources tagged as YSO candidates by Xavier or not?
 +
#EXTRA BONUS, especially when circling back to this step - are there any sources you can identify in this diagram that might be worth a second look in SED or images?
  
Most of the yellow boxes also have a red circle underneath. but there are many, especially in the region with no wise sources in the catalog, where i can see something in the image, it's just not in the catalog. there are several of these. i
+
Notes: For a W1-W2 vs W3-W4 plot. W1-W2 is (should be) centered on zero, because most of the objects seen in W1 and W2 are plain stars, so the color is zero. W3-W4 is notably NOT zero, because the only objects seen at W4 are the ones notably bright at W4, so they all are brighter than plain stars at W4. This is going to be a different morphology than a I1-I2 vs I3-I4 plot, where a much larger number of sources are seen, and a large fraction of those are plain stars. This gave me heart failure during the 2012 summer visit until I realized this. For a K vs. W1-W4 plot, or a W1 vs. W1-W4 plot... The YSO candidates are bright and red, generally. There are other CMDs you can try. See any of the literature we read in the Spring for ideas. After we include some optical data, there will be even more CMDs we can try. We will come back to this step.
count 8 or 10 at least. most of these already have IRAC photometry, so we probably have enough to work with them. only a few are going to be problem children. for the purposes of the poster we can just 'punt' and say "these can be seen in the wise image but we don't yet have wise photometry for them." in the long term, we will either have to persuade the wise team to do the photoemtry for them, or we will do aperture photoemtry on the UNCALIBRATED wise image for these targets and ~10-20 others of comparable brightness that ARE in the wise catalog and then bootstrap the calibration and interpolate what the wise photometry of these objects really are.
 
  
we will have to make note of any others that are in the 'known yso' list, within 20 arcmin of the center (eg not in the corners), and missing wise photometry, then go look into them.
+
=Data Tables, part 2=
  
=Bandmerging the photometry=
+
<font color="red">PARTIALLY DONE</font> - need to use regions file on WISE mosaics, answer Q3 below
  
<font color="red">(really just for reference)</font>
+
OK, now we need to do some more advanced things with data tables, not necessarily limited just to those in Excel.
  
This step was an explicit step in the journal articles we read, so I'm leaving it in here as a conceptual step. For our project, the WISE data is already matched to 2MASS, so we don't need to do that. I already merged all the literature photometry together into one file, so we don't need to do that. We need to merge the WISE catalog to the literature catalog, as well as the Spitzer and optical photometry we're going to do below. You have already done at least some of the WISE-to-literature merging above. Conceptually, we need to bandmerge before we can make color-color plots, which is why this step is here.
+
'''Big picture goal''': More on manipulating data tables. Cope with source list proliferation. ds9 regions files.
  
'''Big picture goal''': Understand what this process is, since there were questions about it when we were reading the literature.
+
'''More specific shorter term goals''': Look at sources in WISE image. Learn how to use ds9 regions files. Possibly identify sources that might have Spitzer data in prep for photometry.
  
'''More specific shorter term goals''': You identified some of the literature objects above in the WISE catalog. For at least some of them, identify which of these objects are in the WISE catalog, and add the photometry (and errors) for those bands to the row for each object. You will have a LOT of Excel columns, especially when you get into the flux conversions for SEDs below. You may wish to start pulling off just the YSOcandidates+literature sources (out of the entire catalog) into at least a separate workbook tab.
+
'''Tasks and Questions for you''':  
 +
#For each of the ''*known*'' objects, you have the RA/Dec - find some of the objects in the images you obtained above. (Hint: you want a ds9 regions file: [[file:brc38knownysos.reg.txt]] is the file for just the known ysos. The file off the DVD that has "withnames" in the filename also prints the row number on top of the region.)  Take notes on any that look like the photometry may be corrupted or that you can easily dismiss as galaxies or other contaminants now that you are looking at better and/or different data than they had before. <font color="green">TEST SAMPLE: the first 4 previously known objects in the 'interesting' list (row numbers 1127, 1144, 1352, 1682)</font> (hint to find them in the image: they are sorted by, and therefore numbered by, RA). Which objects have a WISE match? Which might we worry about?
 +
#BONUS ONLY IF YOU ARE INTERESTED IN BANDMERGING ... For each of the known YSOs (identified in the 'interesting' file), you have the RA/Dec - find the same objects in the big WISE catalog. Which objects are the matches? What constitutes a 'match'? Are there any with no matches?  Spot check a few of my matches between strictly literature catalogs. Did I match them correctly? Which ones are the same between papers and which are new to just one paper?
 +
#Now, start to pull together stuff from this step plus those above.  You can plot RA/Dec of everything. Here, I've done this both in an x/y plot and overplotted on the image (click to get a big one). The first one has several types of objects (defined in plot itself) plotted just in a graph; the second one just has the "sources of interest" (==previously identified YSOs+new candidate YSOs), overplotted on the WISE-1 image (the green circle is the 20 arcmin radius circle that defines our region of interest.
 +
<gallery widths="100px" heights="100px">
 +
file:Brc38where1jul2013.png
 +
file:Brc38where2jul2013.png
 +
</gallery>
 +
Why are there some regions where WISE sources are missing? Are they really missing, or just missing from the catalog? Why are the Spitzer sources where they are? Why is there a patch of black in the center of the plot on the left (hint: Beltran et al.)?
 +
#Can you identify which objects are likely to be in the region of Spitzer coverage? (Hint: I would do this using ds9 regions files and the Spitzer mosaics.) You will need this in order to complete the next section.
  
'''Relevant links''': [[Resolution]]
+
Things to note:
 +
*We did a cone search on the wise catalog, and Xavier made a square mosaic. So we 'lose' the corners. which is fine; we have a ton of other things to worry about with the objects we have.
 +
*There are far more sources seen at w1 that w4 (and you should know why by now!) :) most of the WISE sources are nicely on sources seen in w1; there are far fewer sources in the w4 image (as per large-scale image inspection above!).
  
 
'''For completeness''': The WISE catalog provides some matches to 2MASS, but it is unclear to me exactly where those matches come from, like which sources out of the 2MASS catalog did they use (which error flags did they keep, or did they just look for any matches in the 2MASS catalog?). When I take the WISE catalog's 2MASS matches and compare it to the 2MASS catalog I pull out of Gator myself, I find about 3% fewer matches than the WISE catalog does. I use a matching tolerance of 1 arcsec to match up sources. These 'extra' 3% must be either objects matched to the WISE source that are more than 1 arcsec away, or with a different set of error flags than I would use coming out of 2MASS. What this means in practice is that: (a) we can keep and use the WISE catalog's matches to the 2MASS sources; (b) we should remember this caveat, and if we notice any 2MASS data downstream from here that is weird (like a mismatch in the SED), then we should go back and check those 2MASS matches by hand with the original 2MASS catalog.
 
'''For completeness''': The WISE catalog provides some matches to 2MASS, but it is unclear to me exactly where those matches come from, like which sources out of the 2MASS catalog did they use (which error flags did they keep, or did they just look for any matches in the 2MASS catalog?). When I take the WISE catalog's 2MASS matches and compare it to the 2MASS catalog I pull out of Gator myself, I find about 3% fewer matches than the WISE catalog does. I use a matching tolerance of 1 arcsec to match up sources. These 'extra' 3% must be either objects matched to the WISE source that are more than 1 arcsec away, or with a different set of error flags than I would use coming out of 2MASS. What this means in practice is that: (a) we can keep and use the WISE catalog's matches to the 2MASS sources; (b) we should remember this caveat, and if we notice any 2MASS data downstream from here that is weird (like a mismatch in the SED), then we should go back and check those 2MASS matches by hand with the original 2MASS catalog.
  
=Interjection from Luisa (originally from Wednesday afternoon ppt, Jul 2012)=
+
=Doing Spitzer photometry=
 +
 
 +
<font color="red">DONE for the test set.</font> (Ultimately need to do for all sources of interest with Spitzer data - look at batch processing ("source list") photometry in APT.)
  
*We have a bunch of literature-identified YSOs. (*litdata*yso* files above)
+
OK, this step is going to take the longest, be the most complex, and involve the most steps out of everything (so far, anyway!).  
*We have a bunch of CANDIDATE YSOs identified by Xavier out of the WISE+2MASS catalog.
 
*NOT ALL OF THESE LITERATURE YSOs WILL BE REDISCOVERED BY XAVIER. There will be some undetected, or some without IR excesses. That is why I assembled the "table of interesting objects" ([[file:tableforvisit27_interesting.txt]]), which consists of anything that anyone else tagged as a YSO PLUS anything that Xavier tagged as possibly a YSO.
 
*NOT ALL OF THESE CANDIDATES WILL BE REAL YSOs. There will be MANY contaminants.
 
*One way we weed out the contaminants is to assemble color-mag and color-color plots and look at where the objects fall in those diagrams. (A start on this is the next step; we will come back to it.)
 
*Another way we weed these out is to assemble SEDs (with as much data as we can) and look at them. (Another step below, which will also be visited more than once.)
 
*Another way we weed these out is to look at the images everywhere we can. (Another step below, which will also be visited more than once.)
 
  
 +
'''Never just trust that the computer has done it right. It probably did what you asked it to do correctly, but maybe you asked it to do the wrong thing. '''Always''' make some plots to test and see if the photometry seems correct.'''
  
=Making color-color and color-magnitude plots=
+
'''Big picture goal''': Understand what photometry is, and what the steps are to accomplish it.  Ultimately, do Spitzer photometry on a source-by-source basis for the 'interesting' sources. Understand the units of Spitzer images.  Understand how to assess if your photometry makes sense.
  
<font color="red">(toe-dipped for brc27, indefinitely pending for other two)</font>
+
'''More specific shorter term goals''': For now, just do Spitzer photometry in all bands for a short list of test guys.  Assess whether your photometry seems right.
  
OK, fair warning, some math involved, and the start of ''programming'' spreadsheets!
+
'''Relevant links''':
 +
*[[Units]]
 +
*[[Photometry]]
 +
*[[I'm ready to go on to a more advanced discussion of photometry]]
 +
*[[Aperture photometry using APT]], specifically [[Aperture_photometry_using_APT#Looking_for_a_cookbook.3F|this]], which is the closest thing to a cookbook I will give you. <font color="orange">THIS IS THE PAGE THAT HAS THE STEPS AND THE APERTURE/ANNULUS COMBINATIONS AND APERTURE CORRECTIONS IN IT</font>
 +
*[http://www.youtube.com/watch?v=_w_5DgB0vKw YouTube video on using APT], including calculating the number APT needs.  (15 min because it starts from software installation and goes through doing photometry.)
 +
*[http://www.youtube.com/watch?v=vmn4zX0bRrU YouTube video on photometry in general] (from NITARP tutorials)
 +
*[http://www.youtube.com/watch?v=5lXAWfBW_NQ YouTube video overview of APT] (from NITARP tutorials)
  
'''Big picture goal''': Understand what plots to make. Understand the basic idea of using them to pick out certain objects.
+
To start, we should decide as a group which small set of sources to measure, and have everyone measure the same sources. We will then compare all of our measurements among the whole group. Ultimately, we will need to measure photometry for everything we care about that falls in the Spitzer maps. <font color="green">'''NEARLY ARBITRARILY''', I've picked 5384, 3704, 4009, 3896 as some good test particles.</font>
  
'''More specific shorter term goals''': Make some color-color and color-mag plots using the data imported into Excel in the last step. Understand at least the first few steps of the Koenig et al method in detail. If you can, program the spreadsheet to make the color cut and keep track of which objects pass or fail. At the very least, make a plot of the entire distribution and highlight the YSO candidates from Xavier.  
+
The measurements you get from the Spitzer images are in flux density, e.g., they will come in Jy (microJy or milliJy). It is easier to compare measurements if you convert these to magnitudes first. Ultimately, you need magnitudes for use in color-color and color-mag diagrams anyway. You will also need to convert these into the right units for addition to the SEDs. For now, just convert them to magnitudes. See [[Units#Units_of_Spitzer_Photometry]] and [[Central wavelengths and zero points]] for the numbers and formulae you need.
  
'''Relevant links''':  
+
'''Steps''':
*[[Color-Magnitude and Color-Color plots]]
+
#obtain a ds9 regions file for the YSO candidates surviving to this point. (should have from tasks above)
*[[Gutermuth color selection]] - mostly currently Gutermuth color selection; includes analogy with M&Ms. Koenig color selection is similar in concept but uses different bands.
+
#obtain the Spitzer mosaics (should have from tasks above)
*[[Finding cluster members]]  
+
#For each source that we care about in the image, identify x, y in each of the 4 IRAC channels and at least the first MIPS channel (24 microns). '''CAUTION: it is NOT going to be the same x, y in each image''', and the sky coverage will NOT be the same for each channel (meaning that if the source is not in I1 it may be in I2, I4, and M1 but not I3.  Sources WILL have the same RA and Dec, of course. Note that the image, when loaded into APT, is NOT north-up. There are three ways past users came up with to find the object in the image:
*[[Color-color plot ideas]]
+
##load the image into ds9. put north up. find the object. now find the object in the image in APT.
 +
##load the image into ds9. put north up. find the object. note the x and y. type the x and y into APT.
 +
##under APT's tools, look for an option like "object locator" and type in the coordinates. It should be ##h##m##s and -##d##m##s format. One person in 2012 could not make this work. Most of the rest seemed to be able to make this work.
 +
#While you are doing this, make note of the properties in the image of each source; you will need this downstream. Does it look clean or corrupted by a nearby object, an instrumental artifact, bright nebulosity, etc.?
 +
#Go load the image into APT. Explore the parameters so that you understand what is going on. When you are ready to get to work, Measure photometry for all the sources in this image. Make sure the units work out such that you get the right numbers. Repeat for each channel, each Spitzer pointing.
 +
#Add the flux density measurements for the Spitzer bands to your copy (mini copy?) of the master catalog for the corresponding source. ('bandmerging' by hand!)
 +
#For making CMDs/CCDs, you need magnitudes. For making SEDs, you need flux densities. Sometimes you get magnitudes from archives, and sometimes you get flux densities. You need to be able to convert fluently between these quantities. So, convert the flux densities to magnitudes for later use. M=2.5 log (Fvega/F)... see [[Units]]
 +
#When comparing multiple teams' measurements of the brightness of an object, it is easier to do if converted to magnitudes first.
  
 
'''Questions for you''':  
 
'''Questions for you''':  
#Pick at least one color-color or color-magnitude plot to make. Figure out a way to ignore the "no data" flags (exactly what they are depends on which file you are starting from). Does the photometry seem ok? Where are the plain stars?  Where are the IR excess objects? START FROM A COMPLETE WISE CATALOG FOR STARTERS.
+
#Use APT to explore the various parameters. What is a curve of growth?  
#Which objects are selected by Xavier's method as YSO candidates? You may wish to overplot them with a different color/shape symbol. You may wish to try drawing the line segments on the plot too. OVERPLOT XAVIER'S YSOS ON THE SAME PLOT. Note not Xavier's entire catalog, but just the YSO candidates.
+
#What are the best parameters to use? (RTFM to find what the instrument teams recommend.)  What are the implications of those choices? What happens if you use other choices?
#Are the literature sources tagged as YSO candidates by Xavier or not? You may wish to add them with another color/shape symbol. I DO NOT BELIEVE WE GOT TO THIS.
+
#Does the addition of the Spitzer points change your opinion on which YSO candidates are going to survive to the end of this process?
#''Optional'' next step (may help with larger concepts, or doing this yourself from scratch) - [[Taurus catalog]] has a catalog of legitimate young stars. Where do these objects fall with respect to either the Gutermuth or Koenig colors? Which ones would be retrieved or lost by these color selections? Do the YSO candidates that Xavier sent us have colors like (most of) these YSOs? (Hint: Make a color-color or color-magnitude plot of the entire distribution in the catalog, highlight the YSO candidates with one color symbols, and add the Taurus YSOs to the plots using a different color symbol.)
+
#Look at the new photometry with a critical eye. Which points look like they should be double-checked?
 
 
'''Updates added July 2012''':
 
*When reading in Xavier's file, it is tab-delimited.
 
*When reading in the wise.tbl file, get rid of the first 110 lines, and then parse both on spaces and "another character" (tick that box) and enter "pipe" (which means something in wikitext, so I can't enter it, but it is commonly the character obtained by hitting shift and the \ key (often above your enter key).
 
*Most of the group accomplished a W1-W2 vs W3-W4 plot. W1-W2 is centered on zero, because most of the objects seen in W1 and W2 are plain stars, so the color is zero. W3-W4 is notably NOT zero, because the only objects seen at W4 are the ones notably bright at W4, so they all are brighter than plain stars at W4. This gave me a minor heart attack until I figured it out.
 
*Some of the group accomplished a K vs. W1-W4 plot, or a W1 vs. W1-W4 plot. These look like what I expected. The YSO candidates are bright and red, generally.
 
*There are other CMDs you can try. See the CG4 paper or the Taurus paper or Xavier's paper (appendix) for ideas.
 
*After we get some optical data, there will be even more CMDs we can try. We will come back to this.
 
  
 
=Investigating the images of the objects=
 
=Investigating the images of the objects=
 
<font color="red">July 2012: pending for all of them - put off because can do training for this over the phone</font>
 
 
''This will take some time to complete, and we may not be able to finish it for any one cloud while you are in California.''
 
  
 
'''Big picture goal''': Understand why we need to look at the images of each of our short list of candidates and get started actually doing it and weeding. Also look at any previously identified objects that were not selected by the color cuts.
 
'''Big picture goal''': Understand why we need to look at the images of each of our short list of candidates and get started actually doing it and weeding. Also look at any previously identified objects that were not selected by the color cuts.
Line 226: Line 258:
 
'''More specific shorter term goals''': Figure out how to get images and/or find these things in our images. Calibrate your eyeball for the various images/resolutions/telescopes to figure out what is extended/corrupted/galaxy-like and what isn't. Drop the bad objects off our candidate YSO list.
 
'''More specific shorter term goals''': Figure out how to get images and/or find these things in our images. Calibrate your eyeball for the various images/resolutions/telescopes to figure out what is extended/corrupted/galaxy-like and what isn't. Drop the bad objects off our candidate YSO list.
  
You will need to obtain images of the objects in at least WISE, POSS, and 2MASS. You can do this using the WISE archive and IRSA finder chart, or the big images from before coupled with ds9 regions files. Either way, it takes time. I recommend doing all the WISE first using the WISE archive interface (you can submit a batch list of targets), then all the 2MASS+POSS separately as a second pass using Finder Chart or the WISE archive interface. (You will ultimately need to examine the images from Spitzer and our optical data too, but let's hold off on this for just now.For each of these image sets, it will take a while to calibrate your eyeball, so you will probably need to do the whole list, and then go back and redo the first several or so to be sure that you have it right.  ''REAL examples of non-point source things'': (a) search in Spitzer on HIP 32435 for MIPS 24 um data. Several of the mosaics there contain only point sources. One, though, centered on this target, does not look like all the others. I think this is a star superimposed on a background galaxy. What do you think? (b) search in WISE on "LEDA1684111". This object passes Xavier's photometry cuts for having colors like a YSO. Does it look like the other point sources in the image? I think it looks like a galaxy, or possibly source confusion (e.g., two point sources very close to each other)
+
You will need to obtain images of the 'interesting' objects in WISE, POSS, and 2MASS. You can do this using the IRSA [http://irsa.ipac.caltech.edu/applications/finderchart/ FinderChart], or the big images from before coupled with ds9 regions files. Either way, it takes time; I think it goes much faster with FinderChart. You can submit a batch list of targets. For the objects that have Spitzer data, you will also need to examine these images, but presumably in the APT step above, you have already done some if not all of this image assessment.   For each of these image sets, it will take a while to calibrate your eyeball, so you will probably need to do the whole list, and then go back and redo the first several or so to be sure that you have it right.   
 +
 
 +
<font color="green">'''Test set''':</font> This list represents a set of things not in BRC 38 that I deliberately picked so as to show you the range of things you might find in BRC 38, but are of a wider variety than we are likely to find in BRC 38. Some are deliberately tricky. After you do these, feel free to start on the BRC 38 set. [[file:imagetestsetblank.xlsx]] also see [[file:imagestestsetblank.tbl.txt]], which is a tbl file of this list, suitable for bulk uploading to FinderChart or other IRSA tools with this look-and-feel.  
  
 
'''Relevant links''':   
 
'''Relevant links''':   
 
*[[How can I get data from other wavelengths to compare with infrared data from Spitzer?]]   
 
*[[How can I get data from other wavelengths to compare with infrared data from Spitzer?]]   
 
*[[Resolution]] (specifically some of the concrete examples there)  
 
*[[Resolution]] (specifically some of the concrete examples there)  
*[http://irsa.ipac.caltech.edu/applications/wise/ WISE archive]
+
*[http://irsa.ipac.caltech.edu/applications/finderchart/ IRSA finder chart] itself (direct link)
*[http://irsa.ipac.caltech.edu/applications/FinderChart/ IRSA finder chart]
+
*[http://www.youtube.com/watch?v=4RHS497XeHQ YouTube video on using Finder Chart]. To use the small images from FinderChart to also examine larger images, download the FinderChart thumbnail images as FITS files, load them and the larger image(s) into ds9, pick one of the small finder chart images, and then pick 'Frame/Match/Frame/WCS'. All will snap to alignment with North up, on the same scale, with the target object in the center.
*[http://www.youtube.com/watch?v=4RHS497XeHQ YouTube video on using Finder Chart]. To use these small images to also examine larger images, load them (and the larger images) into ds9, pick one of the small finder chart images, and then pick 'Frame/Match/Frame/WCS'. All will snap to alignment with North up, on the same scale, with the object in the center.
 
 
 
'''Files that may be useful''': [[file:tableforvisit27_interesting.txt]] [[file:tableforvisit34_interesting.txt]] [[file:tableforvisit38_interesting.txt]] - generated using more or less the same code as my catalogs of previously known YSOs above, with all their caveats. These files contain anything that is previously known OR provisionally identified as a YSO by Xavier's code.
 
  
'''Questions for you''':
+
'''Questions for you''' (NB: these are questions that you should consider for each source when examining each BRC 38 object, not just the test set here):
#Which objects are still point sources at all available bands?
+
#Which objects are still point sources at all available bands? Keep good notes on this!
 
#Which are instrumental artifacts? Or instrumental hiccups?
 
#Which are instrumental artifacts? Or instrumental hiccups?
 
#Which might have corrupted photometry?
 
#Which might have corrupted photometry?
  
 
=Making SEDs =
 
=Making SEDs =
 
<font color="red">(toe-dipped-in for brc27, indefinitely pending for other two)</font>
 
  
 
WARNING: lots of math and programming spreadsheets here too... '''you WILL do this more than once to get the units right!'''
 
WARNING: lots of math and programming spreadsheets here too... '''you WILL do this more than once to get the units right!'''
Line 251: Line 280:
  
 
'''More specific shorter term goals''': Program a spreadsheet to convert between mags and flux densities.
 
'''More specific shorter term goals''': Program a spreadsheet to convert between mags and flux densities.
Make at least one SED yourself.  Examine the SEDs for all of our candidate objects. Use them to further evaluate the quality of the YSO candidates from the YSO candidate list.
+
Make at least one SED yourself.   
 
 
Make sure you understand how to get the fluxes from the magnitudes. This is not easy to do right the first time, so you will get the wrong answer the first few times you try. ''CAUTION: Sloan bands (including the optical data from Rebull et al. 2012 or new data from FTN) are in AB mags, not Vega mags!'' IPHAS data are in Vega mags.
 
  
You may wish to use the files I gave you in the previous step.
+
Make sure you understand how to get the fluxes from the magnitudes. This is not easy to do right the first time, so you will get the wrong answer the first few times you try.  
  
 
'''Relevant links''':  
 
'''Relevant links''':  
Line 262: Line 289:
 
*[[Central wavelengths and zero points]]
 
*[[Central wavelengths and zero points]]
 
*[[Studying Young Stars]]   
 
*[[Studying Young Stars]]   
*the detailed object-by-object discussion in the appendix of the [http://lanl.arxiv.org/abs/1105.1180 cg4 paper].
 
*maybe [http://www.aavso.org/apass this] would be useful - i just learned about this, and haven't investigated it at all.
 
  
Pick some objects to plot up, maybe some of the previously-identified ones from above would be a good place to start, or the ones you flagged above as having an IR excess. Start with just one. You will ultimately plot log (lambda*F(lambda)) vs log (lambda) -- see the [[Units]] page. It will take time to get the units right, but once you do it right the first time, all the rest come along for free (if you're working in a spreadsheet). Spend some time looking at the SEDs. Look at their similarities and differences. Identify the bad ones, and discuss with the others why/whether to drop them off the list of YSO candidates.  See also stuff above about data at other wavelengths, and include literature/archival data from other sources where appropriate and possible. Make sure to keep careful track of those things that are limits rather than detections.
+
We will ultimately need to make SEDs for everything, but for purposes of this example, let's work with the <font color="green">same test set of four as we worked with for Spitzer photometry above: 5384, 3704, 4009, and 3896.</font>  Start with just one. You will ultimately plot log (lambda*F(lambda)) vs log (lambda) -- see the [[Units]] page. It will take time to get the units right, but once you do it right the first time, all the rest come along for free (if you're working in a spreadsheet). Spend some time looking at the SEDs. Look at their similarities and differences. Identify the bad ones, and discuss with the others why/whether to drop them off the list of YSO candidates.  See also stuff above about data at other wavelengths, and include literature/archival data from other sources where appropriate and possible. Make sure to keep careful track of those things that are limits rather than detections.
 +
 
 +
Another try at explaining:
 +
*''What do you have?'' UBVRIriHalpha, JHK, WISE data in Vega mags. IRAC, MIPS data in microJanskys.
 +
*''What do you need to get?'' everything into Jy, which are units of Fnu. Then convert your Fnu in Jy into Fnu in cgs units, ergs/s/cm2/Hz, so multiply by 10^-23. Then convert your Fnu into Flambda in cgs units, so multiply by c/lambda^2, with c=2.99d10 cm/s and lambda in cm (not microns!).  Then get lambda*Flambda by multiplying by lambda in cm.  Plot log (lambda*Flambda) vs. log (lambda).
 +
*Once you make your first SED correctly, the rest are easy. But that first one is hard.
 +
*Then you need to look through each of the SEDs and decide which look like you expect, which need photometry to be checked, and which seem unlikely to be legitimate YSOs. This is a judgement call, and your judgement will improve with time as you gain some experience.
  
 
'''Questions for you''':
 
'''Questions for you''':
#What do the IR excesses look like in your plots?  Do they look like you expected? Like objects in CG4 or Monday's ppt or elsewhere?
+
#What do the IR excesses look like in your plots?  Do they look like you expected? Like objects in Monday's ppt or elsewhere?
#Make some SEDs of things you know are ''not'' young stars for comparison - pick some with zero IR color. What do they look like?
+
#Find some SEDs of things you know are ''not'' young stars for comparison - pick some with zero IR color. (You may be able to find some sources with zero color among the previously identified YSOs). What do they look like?
#Which objects look like clear YSO SEDs? Which objects do not?
+
 
#What's the deal with this one (why does it look like this)? (In my SED, the y-axis units are cgs units [sorry], *=FTN data, +=optical literature data, diamonds=2mass, circles=irac, stars=WISE, arrows=limits, and boxes=MIPS if they exist, which they don't here.)
+
=Assessing SEDs =
[[file:chauhan109sed.png]]
+
 
 +
Now that you've made some SEDs, we need to next look at them with a critical eye.
 +
 
 +
'''Big picture goal''': Understand what to expect in a YSO SED and how to discard objects for having questionable SEDs (or put them on the list for checking source matching, photometry, etc).
  
'''Updates added July 2012''':
+
'''More specific goals''': Examine the SEDs for all of our candidate objects. Use them to further evaluate the quality of the YSO candidates from the YSO candidate list.
*''What do you have?'' UBVRI, JHK, WISE data in Vega mags. ri data in AB mags. IRAC, MIPS data in microJanskys.
 
*''What do you need to get?'' everything into Jy, which are units of Fnu. Then convert your Fnu in Jy into Fnu in cgs units, ergs/s/cm2/Hz, so multiply by 10^-23. Then convert your Fnu into Flambda in cgs units, so multiply by c/lambda^2, with c=2.99d10 cm/s and lambda in cm (not microns!).  Then get lambda*Flambda by multiplying by lambda in cm.  Plot log (lambda*Flambda) vs. log (lambda).
 
*I believe that most of you were just trying to get JHK+WISE bands onto an SED. Ultimately, you need to get "all the bands we can" on each SED for each "interesting" object.  We have UBVRI for several literature objects. We have FTN r,i for lots of objects near the middle (and will get more). We have IRAC, MIPS data for SOME of the sources. We can obtain more for SOME of the remaining ones.
 
*Once you make your first SED correctly, the rest are easy.
 
*Then you need to look through each of the SEDs and decide which look like you expect, which need photometry to be checked, and which seem unlikely to be legitimate YSOs. This is a judgement call, and your judgement will improve with time, just as it did for the source matching in the Spring.
 
*The issue with Chauhan109 above is that there is a bright nebulous patch in the WISE images that either is being inappropriately tagged as a point source (with its flux densities attached to this source) or whose brightness is contaminating the photometry beyond recovery. The Spitzer data is critical for sorting out what is going on here. This will not be the first time we are grateful for Spitzer data. (And I still don't know what is going on with the optical data - it's wrong for this source, but this is the best possible match given the information we have in the literature.
 
  
 +
'''Relevant links''':
 +
*[[Studying Young Stars]] 
 +
*the detailed object-by-object discussion in the appendix of the [http://lanl.arxiv.org/abs/1105.1180 cg4 paper].
  
=Doing Spitzer photometry=
+
<font color="green">'''Test set''':</font> This list represents a set of things not in BRC 38 (they actually are all BRC27) that I deliberately picked so as to show you the range of things you might find in BRC 38, but are of a wider variety than we are likely to find in BRC 38. Some are deliberately tricky. After you do these, feel free to start on the BRC 38 set using the SEDs you made in the prior step. [[file:sedtestsetblank.xlsx]] and [[file:brc27trainingjustSEDs.pptx]]
  
<font color="red">toe-dipped-in for BRC 27; indefinitely pending for the other two BRCs</font>
+
<font color="green">'''For the BRC 38 set,'''</font> after you make all the SEDs, you will need to spend some time really looking at the SEDs -- all of them! -- but for now, return to the set of four test SEDs you made above. Look at their similarities and differences. Identify the bad points, and discuss with the others why/whether to drop them off the list of YSO candidates.  See also stuff above about data at other wavelengths, and include literature/archival data from other sources where appropriate and possible. Make sure to keep careful track of those things that are limits rather than detections. Compare your notes on SEDs with notes on images (e.g., if it's tagged "iffy" in images and "iffy" in SEDs, chances are excellent that it is not a good candidate).
  
OK, this step is going to take the longest, be the most complex, and involve the most steps out of everything so far.  
+
'''Questions for you''':
 +
#Which objects look like clear YSO SEDs? Which objects do not? Keep good notes on this throughout BRC 38!
 +
#What's the deal with this one (why does it look like this)? (In my SED, the y-axis units are cgs units [sorry], *=FTN data, +=optical literature data, diamonds=2mass, circles=irac, stars=WISE, arrows=limits, and boxes=MIPS if they exist, which they don't here.) 
 +
[[file:chauhan109sed.png]]
  
<font color="red">Never just trust that the computer has done it right. It probably did what you asked it to do correctly, but maybe you asked it to do the wrong thing. '''Always''' make some plots to test and see if the photometry seems correct.</font>
 
  
'''Big picture goal''': Understand what photometry is, and what the steps are to accomplish it. Do photometry on a source-by-source basis for the 'interesting' sources. Understand the units of Spitzer images.  Understand how to assess if your photometry makes sense.
+
Answer: This source is near a bright nebulous patch in the WISE images that either is being inappropriately tagged as a point source (with its flux densities attached to this source) or whose brightness is contaminating the photometry beyond recovery. The Spitzer data are critical for sorting out what is going on here. And I still don't know what is going on with the optical data - it's apparently wrong for this source, but this is the best possible match given the information we have in the literature, so maybe the people who wrote the paper with the optical data screwed something up either in bandmerging or in their photometry.
  
'''More specific shorter term goals''': Do photometry on all the Spitzer mosaics for the sources that have survived so far as YSO candidates (or YSOs from the literature).  Assess whether your photometry seems right. Add it to the SEDs. 
+
=Assembling the Keepers and Duds=
  
'''Relevant links''':
+
'''Goal:''' Make progress towards assembling final list of things we think are real YSO candidates and those we think are junk.
*[[Units]]
 
*[[Photometry]]
 
*[[I'm ready to go on to a more advanced discussion of photometry]]
 
*[[Aperture photometry using APT]], specifically [[Aperture_photometry_using_APT#Looking_for_a_cookbook.3F|this]], which is the closest thing to a cookbook I will give you.
 
*[http://www.youtube.com/watch?v=_w_5DgB0vKw YouTube video on using APT], including calculating the number APT needs.  (15 min because it starts from software installation and goes through doing photometry.)
 
  
To start, we should decide as a group which small set of sources to measure, and have everyone measure the same sources. We will then compare all of our measurements among the whole group. Ultimately, we will need to measure photometry for everything we care about that falls in the Spitzer maps.
+
By this point, you have (will have) a set of objects identified from the literature or from Xavier, and you should have (will have) notes on each of the objects, obtained from the literature check, the image check, and the SED check. Collate all of these such that you can tag objects as "unlikely to be real YSOs", or "literature YSOs (that may or may not have a disk)", or "still surviving as new YSO candidates".
  
The measurements you get from the Spitzer images will come in Jy (microJy or milliJy). You will need to convert these into the right units for addition to the SEDs. And, probably, you will need to convert these flux densities back into magnitudes for use in color-color and color-mag diagrams, though we may or may not get to this point in July.
+
=Revisiting CMDs and CCDs=
  
'''Steps''':
+
'''Goal:''' We have more data, so we should use it to refine our list of true YSO candidates vs. junk.
#obtain a ds9 regions file for the YSO candidates surviving to this point. (should have from tasks above)
 
#obtain the big Spitzer mosaics (should have from tasks above)
 
#For each source in the image, identify x, y in each of the 4 IRAC channels and at least the first MIPS channel (24 microns). You should look at the MIPS-2 (70 microns) images, but few sources are expected in this channel. '''CAUTION: it is NOT going to be the same x, y in each image''', and the sky coverage will NOT be the same for each channel (meaning that if the source is not in I1 it may be in I2, I4, and M1 but not I3.  Sources WILL have the same RA and Dec, of course.
 
#While you are doing this, make note of the properties in the image of each source. Does it look clean or corrupted by a nearby object, an instrumental artifact, etc.?
 
#Go load the image into APT. Explore the parameters so that you understand what is going on. When you are ready to get to work, Measure photometry for all the sources in this image. Make sure the units work out such that you get the right numbers. Repeat for each channel, each Spitzer pointing.
 
#Add the photometry for the Spitzer bands to your master catalog for the corresponding source. ('bandmerging' by hand again!)
 
#Convert the flux densities to magnitudes for later use. (you may put this off until later if time is short)
 
#Make SEDs for these objects using these additional points.  
 
  
 +
By this point you should have (will have) a list of things that have survived tests. We have optical data for a lot of these objects. You can make optical CMDs and see if the "literature YSOs (that may or may not have a disk)" and "still surviving as new YSO candidates" fall in the 'right place' in these diagrams. For context, take all the optical data we have for all the objects in the region and plot r vs r-i from the IPHAS data. Overplot the survivors on this diagram. Are they where they should be (above the ZAMS)? Do this again, but for r-Halpha vs. r-i.  Are the survivors where they should be (substantially above the unreddened main sequence locus)? Tag any of the survivors as less likely if they don't meet these criteria.
  
'''Questions for you''':
+
=Analyzing SEDs=
#Use APT to explore the various parameters. What is a curve of growth?
 
#What are the best parameters to use? (RTFM to find what the instrument teams recommend.)  What are the implications of those choices? What happens if you use other choices?
 
#Does the addition of the Spitzer points change your opinion on which YSO candidates are going to survive to the end of this process?
 
#You can repeat this on the optical data, but Russ has helpfully reduced the data we have so far. Obtain the full catalog, identify the source matches, and add those points to their corresponding SEDs. CAUTION: these are AB mags, not Vega mags. Does the addition of the optical points change your opinion on which YSO candidates are going to survive?
 
#Look at the new photometry with a critical eye. Which points look like they should be double-checked?
 
  
'''Updates added July 2012''':
+
'''This is advanced, and we may not get here.''
*We only barely got started on this. I picked 5 sources to try, semi-randomly:
 
**07040225-1125429
 
**07040994-1118251
 
**07040234-1125393 (awfully close to first one)
 
**07040123-1122426 (fainter)
 
**07040215-1125122 (fainter)
 
and I picked badly for at least 2 or 3 of the 5. The last two on the list are probably the best ones to try, and we will probably agree better on those (once you get to them) than the first three.
 
*The image, when loaded into APT, is NOT north-up. There are three ways we came up with to find the object in the image:
 
**load the image into ds9. put north up. find the object. now find the object in the image in APT.
 
**load the image into ds9. put north up. find the object. note the x and y. type the x and y into APT.
 
**under APT's tools, look for an option like "object locator" and type in the coordinates. It should be ##h##m##s and -##d##m##s format. One person could not make this work. Most of the rest seemed to be able to make this work.
 
*For making CMDs/CCDs, you need magnitudes. For making SEDs, you need flux densities. Sometimes you get magnitudes from archives, and sometimes you get flux densities. You need to be able to convert fluently between these quantities.
 
*When comparing multiple teams' measurements of the brightness of an object, it is easier to do if converted to magnitudes first.
 
  
 +
Add a new column in Excel to calculate the slope between 2 and 8 microns in the log (lambda*F(lambda)) vs log (lambda) parameter space. This task only makes sense for those objects with both K band and IRAC-4 detections.  (For very advanced folks: ''fit'' the slope to all available points between K and IRAC-4 or MIPS-24.  How does this change the classifications, if at all?)
 +
*if the slope > 0.3 then the class = I
 +
*if the slope < 0.3 and the slope > -0.3 then the class = 'flat'
 +
*if the slope < -0.3 and the slope > -1.6 then class = II
 +
*if the slope < -1.6 then class = III
 +
These classifications come from Wilking et al. (2001, ApJ, 551, 357); yes, they are the real definitions  ([[Studying Young Stars|read more about the classes here]])!
 +
#How many class I, flat, II and III objects do we have?
 +
#Where are the objects with infrared excesses located on the images? Are all the Class Is in similar sorts of locations, but different from the Class IIIs?
  
 +
For very advanced folks: [http://cfa-www.harvard.edu/youngstars/dalessio/ suite of online models from D'Alessio et al.] and [http://caravan.astro.wisc.edu/protostars/ suite of online models from Robitaille et al.].  Compare these to the SEDs we have observed.
  
=Putting this in context a little=
+
=Putting this in context a little: Methodology=
  
 
This step is important for this particular project, because of the nature of the existing literature for the objects we are studying. Again, we may or may not get to this before you leave California.
 
This step is important for this particular project, because of the nature of the existing literature for the objects we are studying. Again, we may or may not get to this before you leave California.
Line 349: Line 361:
 
'''More specific shorter term goals''': Knowing what you do now, go back and reread Chauhan et al. and Choudhury et al. Do a detailed comparison of our method for finding young stars and that from those two papers.  
 
'''More specific shorter term goals''': Knowing what you do now, go back and reread Chauhan et al. and Choudhury et al. Do a detailed comparison of our method for finding young stars and that from those two papers.  
  
'''Relevant links''': [[How can I find out what scientists already know about a particular astronomy topic or object?]] and [[I'm ready to go on to the "Advanced" Literature Searching section]] and [[C-WAYS Spring work]].
+
'''Relevant links''': [[How can I find out what scientists already know about a particular astronomy topic or object?]] and [[I'm ready to go on to the "Advanced" Literature Searching section]] and [[C-CWEL Journal Club]].
  
 
'''Questions for you''':
 
'''Questions for you''':
Line 357: Line 369:
 
#Did we recover all of the young stars identified in the literature? Some will not have IR excesses, so those will not be recovered by an IR-based color selection.
 
#Did we recover all of the young stars identified in the literature? Some will not have IR excesses, so those will not be recovered by an IR-based color selection.
  
=Analyzing SEDs=
+
=Putting this in context a little: Science=
  
'''This is advanced, and we may not get here.'''
+
'''Goal:''' put our work in context with other literature on BRC38 and other star-forming regions from the literature.
  
Add a new column in Excel to calculate the slope between 2 and 8 microns in the log (lambda*F(lambda)) vs log (lambda) parameter space. This task only makes sense for those objects with both K band and IRAC-4 detections.  (For very advanced folks: ''fit'' the slope to all available points between K and IRAC-4 or MIPS-24.  How does this change the classifications?)
+
How many YSOs with IR excess did we see? How many literature YSOs did not have IR excesses? Do we have any evidence that the YSOs from the literature are not actually YSOs? How many new YSOs did we see? What is the fraction of Class I/flat/II/III? How do those fractions compare to what was found by C-WAYS in BRC 27?
*if the slope > 0.3 then the class = I
 
*if the slope < 0.3 and the slope > -0.3 then the class = 'flat'
 
*if the slope < -0.3 and the slope > -1.6 then class = II
 
*if the slope < -1.6 then class = III
 
These classifications come from Wilking et al. (2001, ApJ, 551, 357); yes, they are the real definitions  ([[Studying Young Stars|read more about the classes here]])!
 
#How many class I, flat, II and III objects do we have?
 
#Where are the objects with infrared excesses located on the images? Are all the Class Is in similar sorts of locations, but different from the Class IIIs?
 
 
 
For very advanced folks: [http://cfa-www.harvard.edu/youngstars/dalessio/ suite of online models from D'Alessio et al.] and [http://caravan.astro.wisc.edu/protostars/ suite of online models from Robitaille et al.].  Compare these to the SEDs we have observed.
 
  
 
=Writing it up!=
 
=Writing it up!=
  
We need to write an AAS abstract and then the poster, and if we're lucky, a paper!
+
'''Goal:''' We need to write an AAS abstract and then the poster, and if we're lucky, a paper!
  
 
We need to include:
 
We need to include:

Latest revision as of 17:21, 7 August 2013

This page is an updated version of the Working with the C-WAYS data page, which was an update of the Working with the BRCs page, which was an update of the Working with CG4+SA101 page, which was an update of the Working with L1688 page. This page was developed and updated specifically for the 2013 C-CWEL team visit.

Please note: NONE of these pages are meant to be used without applying your brain! They are NOT cookbooks! This is presented as a linear progression because of the nature of this page, but we have already done some things "out of order", and moreover, chances are excellent that you will go back and redo different pieces of this at different stages of your work.

FOR REFERENCE: C-CWEL Bigger Picture and Goals

FOR REFERENCE: C-CWEL DVD Contents. Includes instructions on how to force your computer to read any files with an extension you don't recognize (.tbl, .reg).

Useful Positions

(just for reference)

BRC 38: 21:40:42 +58:16:12.8

And, we care about stuff within a ~20 arcmin radius of these positions. (which means 40 arcmin on a side if you are pulling a square rather than a cone.)

Obtaining the data

DONE

We have just one region we care about, so just one place to search on the sky. We need to get the relevant data from both WISE and Spitzer.

WISE -- How do I download data from WISE? has a simple walkthrough, with links to more tutorials. And, Access the WISE archive directly here. You will need to get images and catalogs, both, for a 20 arcmin radius from the center position of BRC 38.

Spitzer -- How do I download data from Spitzer? has a wide variety of flavors of tutorials. The second formal chapter of the professional astronomer's Data Reduction Cookbook ultimately comes from a 2010 NITARP project. I haven't developed one customized to your project. However, as you know, there will only be Spitzer data centered on BRC 38. You will need to find the data, and download the files.

Big picture goal: Get the data you need for this project. Get you comfortable enough to search for your own favorite target in WISE and Spitzer, understand what to do with the search results, and download data.

More specific shorter term goals: Search on our targets. Understand the difference between the observations that are returned. Pick specific observations out of the archive and understand why we picked them. Obtain the relevant catalogs.

Relevant links:

Questions for you:

  1. In WISE, in addition to position, the most important search parameter is the size of the image. What do you need to do to get the data we need?
  2. In Spitzer, because it was not an all-sky survey, there will be only one small observation. In the general case, you might pull up several different observations in your region of interest. For just the BRC 38 observations, compare the various observations you get as search results. How are they the same/different? You'll need just the Level 2 (post-BCD) mosaics.
  3. How do you download source lists from WISE, as opposed to images? The catalog will come with 2MASS matches already done, but you can also get catalogs from 2MASS this way; you will need this below.

Investigating the mosaics

DONE

It is "real astronomy" to spend a lot of time staring at the mosaics and understanding what you are looking at. Don't dismiss this step as not "real astronomy" just because you are not making quantitative measurements. This is time well-spent, and you should plan on investing some time doing this section. Some aspects of this were already discussed in the context of the Resolution worksheet.

For the WISE data, we can use the mosaics as provided by the WISE archive. BRC 38 happens to fall on a boundary between tiles as provided. If you want in the future to make a big mosaic (or a "pretty picture"), we can either use Goddard's Skyview to make mosaics, or MONTAGE. We have mosaics that Xavier made us that are centered on BRC 38 (and I honestly don't know what software he used to generate them). Look on the DVD I gave the educators.

For Spitzer data, in the generic case for most targets, you can probably use the online mosaics that come as PBCD (Level 2) mosaics (or delivered products, if they exist for the region you want -- see "enhanced product search" in the SHA). In this case, we can probably get by just fine with the online mosaics.

Big picture goal: Recognize at a glance what is an instrumental artifact and what is real. Understand what is seen at each WISE and Spitzer band and all the other archival bands.

More specific shorter term goals: Understand what is part of the sky and what is an artifact (e.g., not part of the sky). Recognize how the images differ among the various bands, and why.

Relevant links:

Questions for you:

  1. MOST IMPORTANT of these questions: Compare the mosaics across the bands. What changes? What stays the same? Why? (This is a DEEP question! See also next questions.)
  2. How does the number of stars differ across the bands? Which band has the most stars? The fewest? (Bonus question: why?) The most nebulosity? The least? (Bonus question: why?) Are there more stars in the regions of nebulosity, or less? Why?
  3. What is saturated? Are the same objects saturated in all bands? What are some other instrumental effects you can see? Example Spitzer/MIPS image with substantial artifacts here if you want to train your eye, or see an extreme case. (Bonus: which way was the scan map 'painting' the sky?)
  4. Notice the pixel scale. What is the real pixel scale of the original instrument (WISE, IRAC, MIPS)? What are the pixel scales of the images? Does that actually change the resolution? (for advanced folks - why did we do this?) (You may have already addressed these issues during the Resolution work earlier this year.)
  5. Make a three-color image. What happens when you include a MIPS-24 or WISE-22 mosaic in as one of the three colors with shorter bands as the other two colors? (NB: this might be easiest within the same telescope, e.g., use just WISE bands or just Spitzer bands to make a 3-color image.) Do the stars match up? Does the resolution matter? Can you tell from just a glance at the three-color mosaic which stars are bright at 22 or 24 microns?
  6. How much more detail do you see with Spitzer that was missed by WISE? How do the resolution and sensitivity vary?
  7. BONUS: How big are any of the features in the image (nebulosity, galaxy, space between objects)? (What do I mean by big?) in pixels, arcseconds, parsecs, and/or light years? (Hint: you need to know how far away the thing is. If it helps, there are 3.26 light years in a parsec.)

Getting data from other wavelengths

Mostly already done

You have really already done most of this in your literature search and resolution worksheet this Spring. However, if you don't still have the images you found before on your laptop, you might as well go grab them again (or get my copies off the DVD I gave the educators). You want at the very least POSS and IRAS images.

Big picture goal: Understand how to use the various archives to find non-Spitzer data.

More specific shorter term goals: Go get data for BRC 27 from POSS (images) and 2MASS (images and catalogs) for comparison to our data.

Relevant links:

Questions for you:

  1. Figure out how to get images from at least POSS. (Bonus: 2MASS images too.) Get images covering about 20 arcminutes in radius from the center position so that they are easy to compare, but larger scale images might be useful to give a sense of context too. Watch your pixel scale! Start to look at these images in context of the WISE images. Between POSS and WISE, what is bright, and what is faint? (Bonus: compare 2MASS, POSS, and WISE.) (Still intrigued? Another Bonus: Get IRAS too. Between IRAS and WISE, what breaks into pieces or dissolves into nebulosity when viewed at higher spatial resolution?)
  2. Even though I've already gotten these and matched them for you, it is worth spending a few minutes figuring out how to get catalogs from 2MASS (not images per se!) so that you don't have to depend heavily on me in the future. You can do this via the WISE archive. The WISE catalogs come with some 2MASS matches, but the details of the matching process are sometimes a little obscure, so original 2MASS catalogs are also useful. Get catalogs covering about 20 arcminutes in radius from the center position. This will be a big file.
  3. BONUS: use the catalog trick to get Akari data in our region of interest.

Previously identified sources

Mostly already done

You've already really done the majority of this prior to the visit, but this is where it kind of falls in the logical progression here. (I see the progression as : pick target, get images, get multiwavelength images, get numbers for the sources in the images first from the literature and where others have done it for us, then do more ourselves, then make plots, etc.) In the context specifically of bandmerging (later step), it's probably good to spot-check my matching! But this spot checking is probably done more easily as part of a later 'data tables' step, once you have facility with ds9 and its regions files.

Big picture goal: Understand what has already been studied and what hasn't in the region we care about.

Relevant links:

IMPORTANT: when we are done weeding source lists as per the below, we will have to get into SIMBAD and search for each of our sources, just to get another handle on whether or not anyone has done anything on them before -- because some of our sources are beyond where the prior papers were working, and they just might be something else already identified in the literature.

Bandmerging the photometry

Mostly already done - but PLEASE thoughtfully read this section!

This section could logically go elsewhere in this logical progression, but I think of bandmerging as having two parts -- combining the data from the literature, but also (later) combining data we have measured. Since I've basically done it for you, let's just keep this step here. This step is an explicit step in the journal articles we read.

Big picture goal: Create a master catalog where there is one line per unique object that contains the measurements at all wavelengths and other relevant information all collected on same line. Understand what this process is, since I've already done most of it for you. You need this catalog in order to make color-color and color-magnitude diagrams, and make SEDs.

Relevant links:

For future reference: The WISE data come out of the WISE archive already matched to 2MASS, so generally you don't have to do that. If you pull already reduced data from Spitzer for any given target, you will also most likely have quite a few objects bandmerged already.

Important notes: In this specific case, I've done the merging for you, BUT...:

  • There are four objects that appear in the Choudhury data tables without coordinates, and I cannot locate coordinates for them. I wrote the author, but never heard back. Turns out that the T2 flux densities are also .. off. I can't tell what units they are in, except that they are definitely NOT the units as indicated in the table. More on this flux thing below. But for now I've been forced to just drop the objects without coordinates from our master catalog.
  • Akari data really does just have one source in this region that we might care about (18 over whole region but only 1 tagged before or now as YSO candidate), and Nakano already identified it. It's merged into my db but would mean 4 more columns in your Excel catalog for very little gain, so haven't given it to you.
  • IPHAS data release 2 still not out; the data that were mailed to us by Barentsen do not cover the entire area. Unfortunately, it's missing coverage in the south, the region where we are most likely to have YSOs that are optically detectable. We will work with what we can and watch for the IPHAS data when fully released.
  • Nakano's coordinates are .. not as good as I would have hoped. However, they list the 2MASS match, so I took the 2MASS name and decoded coordinates from that, then went forward with the merging process.
  • Xavier's new WISE color selection routines are far more restrictive than they were a year ago, and as such they omit a lot of the 'garbage' that last year's group had to still cope with. We therefore have a much shorter list than we might have had otherwise! Xavier's old classification scheme was more lenient, but it is possible that the new version discards real YSOs along with all the junk. I've retained the old classification scheme in case we whiz through the new ones and want more to chew on.
  • I get that there are between 20 and 50 objects that potentially have Spitzer data, including those already listed in the literature with one or more Spitzer bands. I did some quick-and-dirty automatic photometry. (This was how I discovered that the Choudhury T2 flux densities were just ..wrong. I match their T1 flux densities pretty well, but not their T2.) There is absolutely no guarantee that what I did is right, especially since I did it 'blind', e.g., just trusting that the computer did it right, not checking to see if the answers were sensible (except via a bulk comparison to literature photometry values).

Data Tables, part 1

Essentially DONE - assuming everyone have xls versions of the full and/or the 'interesting' catalogs...

Hopefully, you already have developed some of these skills via C-CWEL Excel Practice. If not, this is the time to learn!

Big picture goal: Learn how to manipulate data tables. Look at the data tables to identify what you need. Start to cope with source list proliferation.

More specific shorter term goals: Understand how to import plain text tables into Excel (or another spreadsheet of your choice). Really look at the files as retrieved from the WISE archive and look at files as sent by Xavier and determine the relevant information out of these catalogs. Keep track of which files are which.

Relevant links:

  • YouTube video on what tbl files are, how to access them, and specifically how to import tbl files into xls. (10min)

Note that many data tables come with many, many, many lines (like more than 100) at the top explaining what the contents of the file are. These are useful for keeping with the file (like a FITS header is useful to keep with the image), but when reading it into Excel, you may wish to delete all but a note to yourself about what the file is, and the headers of the data columns themselves.

Tasks and Questions for you:

  1. You should have a WISE catalog, either from your earlier download or the DVD. Load that puppy into Excel. Cope with the long header - scan it, keep it elsewhere, but you may not want to read it in to your Excel copy. What information do we need? How do you figure out which ones have bad photometry?
  2. You should have a copy of Xavier's catalog with classifications on the DVD. Load that into another Excel worksheet or file. This one has a lot less documentation within the catalog; its documentation is a separate file, and you will need to consult this to decrypt which sources are YSO candidates and which are not. Figure out how to do this. There may be some utility in keeping the codes (rather than global search and replace).
  3. Are these two files in the same order? (Did you change the order during the prior 'decryption' step? I did!) How could you find out, and fix this if necessary? Do they contain the same number of sources? Can you just copy the classification column out of Xavier's catalog into the WISE catalog? You need to tie Xavier's class to the WISE object, because in the next step, you will need a way of identifying the YSO candidates in plots. Save this file as its own Excel file.
  4. We already have good coordinates from each paper for BRC 38. I bandmerged all these catalogs for you; copies of these files are on the DVD and they should import cleanly into xls, but be careful about the limits (see below).
    1. CAUTION 1: Some of the literature reported whole data tables, and some just reported the YSOs. So there are files from me with everything in the literature (long) and files with just the things someone in the literature tagged as YSOs (short). There are also files from me with just the 'interesting' ones (meaning the literature-identified plus the new Xavier-identified). Because the file of all the 'interesting' sources has a column indicating whether the source is there because it is previously known ("PrevKn") or is in the list because it seems to have a WISE IR excess ("WISEIRx"), you can tell from that column in the 'interesting' files which sources are solely literature ("PrevKn") and which are literature but also seem independently to have an IR excess ("PrevKn+WISEIRx"). The sources you want to work with (for now) are the ones that someone in the literature tagged as YSOs. So, you can use EITHER the 'interesting' file OR the 'justlitysos' files. TO SAVE YOU WORK DOWNSTREAM, SUGGEST YOU LOAD 'INTERESTING' FILE. Save this as its own Excel file or worksheet, separate (tab or file) from the previous step.
    2. CAUTION 2, AND THIS ONE'S A BIGGIE: These catalog files generally have a mixture of detections and limits, measurements and errors, flux densities and magnitudes. You will need to be careful in importing this into Excel. The UBVRIriHalphaJHK are all Vega mags, some have errors and some have limits. The IRAC and MIPS data are all in FLUX DENSITIES (uJy), and often have limits.


Making color-color and color-magnitude plots

Nearly done - need to make/compare CMDs/CCDs

OK, fair warning, some math involved, and the start of programming spreadsheets!

Big picture goal: Understand what plots to make. Understand the basic idea of using them to pick out certain objects.

More specific shorter term goals: Make some color-color and color-mag plots using the complete WISE catalog imported into Excel in the last step. At the very least, make a plot of the entire distribution and highlight the YSO candidates from Xavier.

Relevant links:

Tasks and Questions for you:

  1. To do these next steps, you need a catalog that merges the WISE catalog, the 2MASS catalog, and the catalog from Xavier. If you did all the steps in the prior task, you have this now; I also have a copy of this for you on the DVD.
  2. Start from the complete WISE catalog. Pick at least one color-color or color-magnitude plot to make (Suggestion: W1-W2 vs W3-W4, K vs. W1-W4 plot, or a W1 vs. W1-W4 plot). Figure out a way to ignore the "no data" flags (exactly what they are depends on which file you are starting from - they could be 'null' or they could be '-9'). Does the photometry seem ok? Identify the regions where you expect to find the plain stars and the IR excess objects.
  3. Which objects are selected by Xavier's method as YSO candidates? Overplot them on the same plot as above with a different color and/or shape symbol. You may wish to try drawing the line segments on the plot too.
  4. Bonus - read in one of my catalogs from the DVD that has literature sources indicated (e.g, the 'interesting' file loaded into Excel in the last step). Overplot these on the same plot, with a different color and/or shape symbol. Are the literature sources tagged as YSO candidates by Xavier or not?
  5. EXTRA BONUS, especially when circling back to this step - are there any sources you can identify in this diagram that might be worth a second look in SED or images?

Notes: For a W1-W2 vs W3-W4 plot. W1-W2 is (should be) centered on zero, because most of the objects seen in W1 and W2 are plain stars, so the color is zero. W3-W4 is notably NOT zero, because the only objects seen at W4 are the ones notably bright at W4, so they all are brighter than plain stars at W4. This is going to be a different morphology than a I1-I2 vs I3-I4 plot, where a much larger number of sources are seen, and a large fraction of those are plain stars. This gave me heart failure during the 2012 summer visit until I realized this. For a K vs. W1-W4 plot, or a W1 vs. W1-W4 plot... The YSO candidates are bright and red, generally. There are other CMDs you can try. See any of the literature we read in the Spring for ideas. After we include some optical data, there will be even more CMDs we can try. We will come back to this step.

Data Tables, part 2

PARTIALLY DONE - need to use regions file on WISE mosaics, answer Q3 below

OK, now we need to do some more advanced things with data tables, not necessarily limited just to those in Excel.

Big picture goal: More on manipulating data tables. Cope with source list proliferation. ds9 regions files.

More specific shorter term goals: Look at sources in WISE image. Learn how to use ds9 regions files. Possibly identify sources that might have Spitzer data in prep for photometry.

Tasks and Questions for you:

  1. For each of the *known* objects, you have the RA/Dec - find some of the objects in the images you obtained above. (Hint: you want a ds9 regions file: File:Brc38knownysos.reg.txt is the file for just the known ysos. The file off the DVD that has "withnames" in the filename also prints the row number on top of the region.) Take notes on any that look like the photometry may be corrupted or that you can easily dismiss as galaxies or other contaminants now that you are looking at better and/or different data than they had before. TEST SAMPLE: the first 4 previously known objects in the 'interesting' list (row numbers 1127, 1144, 1352, 1682) (hint to find them in the image: they are sorted by, and therefore numbered by, RA). Which objects have a WISE match? Which might we worry about?
  2. BONUS ONLY IF YOU ARE INTERESTED IN BANDMERGING ... For each of the known YSOs (identified in the 'interesting' file), you have the RA/Dec - find the same objects in the big WISE catalog. Which objects are the matches? What constitutes a 'match'? Are there any with no matches? Spot check a few of my matches between strictly literature catalogs. Did I match them correctly? Which ones are the same between papers and which are new to just one paper?
  3. Now, start to pull together stuff from this step plus those above. You can plot RA/Dec of everything. Here, I've done this both in an x/y plot and overplotted on the image (click to get a big one). The first one has several types of objects (defined in plot itself) plotted just in a graph; the second one just has the "sources of interest" (==previously identified YSOs+new candidate YSOs), overplotted on the WISE-1 image (the green circle is the 20 arcmin radius circle that defines our region of interest.

Why are there some regions where WISE sources are missing? Are they really missing, or just missing from the catalog? Why are the Spitzer sources where they are? Why is there a patch of black in the center of the plot on the left (hint: Beltran et al.)?

  1. Can you identify which objects are likely to be in the region of Spitzer coverage? (Hint: I would do this using ds9 regions files and the Spitzer mosaics.) You will need this in order to complete the next section.

Things to note:

  • We did a cone search on the wise catalog, and Xavier made a square mosaic. So we 'lose' the corners. which is fine; we have a ton of other things to worry about with the objects we have.
  • There are far more sources seen at w1 that w4 (and you should know why by now!) :) most of the WISE sources are nicely on sources seen in w1; there are far fewer sources in the w4 image (as per large-scale image inspection above!).

For completeness: The WISE catalog provides some matches to 2MASS, but it is unclear to me exactly where those matches come from, like which sources out of the 2MASS catalog did they use (which error flags did they keep, or did they just look for any matches in the 2MASS catalog?). When I take the WISE catalog's 2MASS matches and compare it to the 2MASS catalog I pull out of Gator myself, I find about 3% fewer matches than the WISE catalog does. I use a matching tolerance of 1 arcsec to match up sources. These 'extra' 3% must be either objects matched to the WISE source that are more than 1 arcsec away, or with a different set of error flags than I would use coming out of 2MASS. What this means in practice is that: (a) we can keep and use the WISE catalog's matches to the 2MASS sources; (b) we should remember this caveat, and if we notice any 2MASS data downstream from here that is weird (like a mismatch in the SED), then we should go back and check those 2MASS matches by hand with the original 2MASS catalog.

Doing Spitzer photometry

DONE for the test set. (Ultimately need to do for all sources of interest with Spitzer data - look at batch processing ("source list") photometry in APT.)

OK, this step is going to take the longest, be the most complex, and involve the most steps out of everything (so far, anyway!).

Never just trust that the computer has done it right. It probably did what you asked it to do correctly, but maybe you asked it to do the wrong thing. Always make some plots to test and see if the photometry seems correct.

Big picture goal: Understand what photometry is, and what the steps are to accomplish it. Ultimately, do Spitzer photometry on a source-by-source basis for the 'interesting' sources. Understand the units of Spitzer images. Understand how to assess if your photometry makes sense.

More specific shorter term goals: For now, just do Spitzer photometry in all bands for a short list of test guys. Assess whether your photometry seems right.

Relevant links:

To start, we should decide as a group which small set of sources to measure, and have everyone measure the same sources. We will then compare all of our measurements among the whole group. Ultimately, we will need to measure photometry for everything we care about that falls in the Spitzer maps. NEARLY ARBITRARILY, I've picked 5384, 3704, 4009, 3896 as some good test particles.

The measurements you get from the Spitzer images are in flux density, e.g., they will come in Jy (microJy or milliJy). It is easier to compare measurements if you convert these to magnitudes first. Ultimately, you need magnitudes for use in color-color and color-mag diagrams anyway. You will also need to convert these into the right units for addition to the SEDs. For now, just convert them to magnitudes. See Units#Units_of_Spitzer_Photometry and Central wavelengths and zero points for the numbers and formulae you need.

Steps:

  1. obtain a ds9 regions file for the YSO candidates surviving to this point. (should have from tasks above)
  2. obtain the Spitzer mosaics (should have from tasks above)
  3. For each source that we care about in the image, identify x, y in each of the 4 IRAC channels and at least the first MIPS channel (24 microns). CAUTION: it is NOT going to be the same x, y in each image, and the sky coverage will NOT be the same for each channel (meaning that if the source is not in I1 it may be in I2, I4, and M1 but not I3. Sources WILL have the same RA and Dec, of course. Note that the image, when loaded into APT, is NOT north-up. There are three ways past users came up with to find the object in the image:
    1. load the image into ds9. put north up. find the object. now find the object in the image in APT.
    2. load the image into ds9. put north up. find the object. note the x and y. type the x and y into APT.
    3. under APT's tools, look for an option like "object locator" and type in the coordinates. It should be ##h##m##s and -##d##m##s format. One person in 2012 could not make this work. Most of the rest seemed to be able to make this work.
  4. While you are doing this, make note of the properties in the image of each source; you will need this downstream. Does it look clean or corrupted by a nearby object, an instrumental artifact, bright nebulosity, etc.?
  5. Go load the image into APT. Explore the parameters so that you understand what is going on. When you are ready to get to work, Measure photometry for all the sources in this image. Make sure the units work out such that you get the right numbers. Repeat for each channel, each Spitzer pointing.
  6. Add the flux density measurements for the Spitzer bands to your copy (mini copy?) of the master catalog for the corresponding source. ('bandmerging' by hand!)
  7. For making CMDs/CCDs, you need magnitudes. For making SEDs, you need flux densities. Sometimes you get magnitudes from archives, and sometimes you get flux densities. You need to be able to convert fluently between these quantities. So, convert the flux densities to magnitudes for later use. M=2.5 log (Fvega/F)... see Units
  8. When comparing multiple teams' measurements of the brightness of an object, it is easier to do if converted to magnitudes first.

Questions for you:

  1. Use APT to explore the various parameters. What is a curve of growth?
  2. What are the best parameters to use? (RTFM to find what the instrument teams recommend.) What are the implications of those choices? What happens if you use other choices?
  3. Does the addition of the Spitzer points change your opinion on which YSO candidates are going to survive to the end of this process?
  4. Look at the new photometry with a critical eye. Which points look like they should be double-checked?

Investigating the images of the objects

Big picture goal: Understand why we need to look at the images of each of our short list of candidates and get started actually doing it and weeding. Also look at any previously identified objects that were not selected by the color cuts.

More specific shorter term goals: Figure out how to get images and/or find these things in our images. Calibrate your eyeball for the various images/resolutions/telescopes to figure out what is extended/corrupted/galaxy-like and what isn't. Drop the bad objects off our candidate YSO list.

You will need to obtain images of the 'interesting' objects in WISE, POSS, and 2MASS. You can do this using the IRSA FinderChart, or the big images from before coupled with ds9 regions files. Either way, it takes time; I think it goes much faster with FinderChart. You can submit a batch list of targets. For the objects that have Spitzer data, you will also need to examine these images, but presumably in the APT step above, you have already done some if not all of this image assessment. For each of these image sets, it will take a while to calibrate your eyeball, so you will probably need to do the whole list, and then go back and redo the first several or so to be sure that you have it right.

Test set: This list represents a set of things not in BRC 38 that I deliberately picked so as to show you the range of things you might find in BRC 38, but are of a wider variety than we are likely to find in BRC 38. Some are deliberately tricky. After you do these, feel free to start on the BRC 38 set. File:Imagetestsetblank.xlsx also see File:Imagestestsetblank.tbl.txt, which is a tbl file of this list, suitable for bulk uploading to FinderChart or other IRSA tools with this look-and-feel.

Relevant links:

Questions for you (NB: these are questions that you should consider for each source when examining each BRC 38 object, not just the test set here):

  1. Which objects are still point sources at all available bands? Keep good notes on this!
  2. Which are instrumental artifacts? Or instrumental hiccups?
  3. Which might have corrupted photometry?

Making SEDs

WARNING: lots of math and programming spreadsheets here too... you WILL do this more than once to get the units right!

Big picture goal: Understand how to convert magnitudes back and forth to flux densities. Understand what an SED is and why it matters.

More specific shorter term goals: Program a spreadsheet to convert between mags and flux densities. Make at least one SED yourself.

Make sure you understand how to get the fluxes from the magnitudes. This is not easy to do right the first time, so you will get the wrong answer the first few times you try.

Relevant links:

We will ultimately need to make SEDs for everything, but for purposes of this example, let's work with the same test set of four as we worked with for Spitzer photometry above: 5384, 3704, 4009, and 3896. Start with just one. You will ultimately plot log (lambda*F(lambda)) vs log (lambda) -- see the Units page. It will take time to get the units right, but once you do it right the first time, all the rest come along for free (if you're working in a spreadsheet). Spend some time looking at the SEDs. Look at their similarities and differences. Identify the bad ones, and discuss with the others why/whether to drop them off the list of YSO candidates. See also stuff above about data at other wavelengths, and include literature/archival data from other sources where appropriate and possible. Make sure to keep careful track of those things that are limits rather than detections.

Another try at explaining:

  • What do you have? UBVRIriHalpha, JHK, WISE data in Vega mags. IRAC, MIPS data in microJanskys.
  • What do you need to get? everything into Jy, which are units of Fnu. Then convert your Fnu in Jy into Fnu in cgs units, ergs/s/cm2/Hz, so multiply by 10^-23. Then convert your Fnu into Flambda in cgs units, so multiply by c/lambda^2, with c=2.99d10 cm/s and lambda in cm (not microns!). Then get lambda*Flambda by multiplying by lambda in cm. Plot log (lambda*Flambda) vs. log (lambda).
  • Once you make your first SED correctly, the rest are easy. But that first one is hard.
  • Then you need to look through each of the SEDs and decide which look like you expect, which need photometry to be checked, and which seem unlikely to be legitimate YSOs. This is a judgement call, and your judgement will improve with time as you gain some experience.

Questions for you:

  1. What do the IR excesses look like in your plots? Do they look like you expected? Like objects in Monday's ppt or elsewhere?
  2. Find some SEDs of things you know are not young stars for comparison - pick some with zero IR color. (You may be able to find some sources with zero color among the previously identified YSOs). What do they look like?

Assessing SEDs

Now that you've made some SEDs, we need to next look at them with a critical eye.

Big picture goal: Understand what to expect in a YSO SED and how to discard objects for having questionable SEDs (or put them on the list for checking source matching, photometry, etc).

More specific goals: Examine the SEDs for all of our candidate objects. Use them to further evaluate the quality of the YSO candidates from the YSO candidate list.

Relevant links:

Test set: This list represents a set of things not in BRC 38 (they actually are all BRC27) that I deliberately picked so as to show you the range of things you might find in BRC 38, but are of a wider variety than we are likely to find in BRC 38. Some are deliberately tricky. After you do these, feel free to start on the BRC 38 set using the SEDs you made in the prior step. File:Sedtestsetblank.xlsx and File:Brc27trainingjustSEDs.pptx

For the BRC 38 set, after you make all the SEDs, you will need to spend some time really looking at the SEDs -- all of them! -- but for now, return to the set of four test SEDs you made above. Look at their similarities and differences. Identify the bad points, and discuss with the others why/whether to drop them off the list of YSO candidates. See also stuff above about data at other wavelengths, and include literature/archival data from other sources where appropriate and possible. Make sure to keep careful track of those things that are limits rather than detections. Compare your notes on SEDs with notes on images (e.g., if it's tagged "iffy" in images and "iffy" in SEDs, chances are excellent that it is not a good candidate).

Questions for you:

  1. Which objects look like clear YSO SEDs? Which objects do not? Keep good notes on this throughout BRC 38!
  2. What's the deal with this one (why does it look like this)? (In my SED, the y-axis units are cgs units [sorry], *=FTN data, +=optical literature data, diamonds=2mass, circles=irac, stars=WISE, arrows=limits, and boxes=MIPS if they exist, which they don't here.)

Chauhan109sed.png


Answer: This source is near a bright nebulous patch in the WISE images that either is being inappropriately tagged as a point source (with its flux densities attached to this source) or whose brightness is contaminating the photometry beyond recovery. The Spitzer data are critical for sorting out what is going on here. And I still don't know what is going on with the optical data - it's apparently wrong for this source, but this is the best possible match given the information we have in the literature, so maybe the people who wrote the paper with the optical data screwed something up either in bandmerging or in their photometry.

Assembling the Keepers and Duds

Goal: Make progress towards assembling final list of things we think are real YSO candidates and those we think are junk.

By this point, you have (will have) a set of objects identified from the literature or from Xavier, and you should have (will have) notes on each of the objects, obtained from the literature check, the image check, and the SED check. Collate all of these such that you can tag objects as "unlikely to be real YSOs", or "literature YSOs (that may or may not have a disk)", or "still surviving as new YSO candidates".

Revisiting CMDs and CCDs

Goal: We have more data, so we should use it to refine our list of true YSO candidates vs. junk.

By this point you should have (will have) a list of things that have survived tests. We have optical data for a lot of these objects. You can make optical CMDs and see if the "literature YSOs (that may or may not have a disk)" and "still surviving as new YSO candidates" fall in the 'right place' in these diagrams. For context, take all the optical data we have for all the objects in the region and plot r vs r-i from the IPHAS data. Overplot the survivors on this diagram. Are they where they should be (above the ZAMS)? Do this again, but for r-Halpha vs. r-i. Are the survivors where they should be (substantially above the unreddened main sequence locus)? Tag any of the survivors as less likely if they don't meet these criteria.

Analyzing SEDs

This is advanced, and we may not get here.

Add a new column in Excel to calculate the slope between 2 and 8 microns in the log (lambda*F(lambda)) vs log (lambda) parameter space. This task only makes sense for those objects with both K band and IRAC-4 detections. (For very advanced folks: fit the slope to all available points between K and IRAC-4 or MIPS-24. How does this change the classifications, if at all?)

  • if the slope > 0.3 then the class = I
  • if the slope < 0.3 and the slope > -0.3 then the class = 'flat'
  • if the slope < -0.3 and the slope > -1.6 then class = II
  • if the slope < -1.6 then class = III

These classifications come from Wilking et al. (2001, ApJ, 551, 357); yes, they are the real definitions (read more about the classes here)!

  1. How many class I, flat, II and III objects do we have?
  2. Where are the objects with infrared excesses located on the images? Are all the Class Is in similar sorts of locations, but different from the Class IIIs?

For very advanced folks: suite of online models from D'Alessio et al. and suite of online models from Robitaille et al.. Compare these to the SEDs we have observed.

Putting this in context a little: Methodology

This step is important for this particular project, because of the nature of the existing literature for the objects we are studying. Again, we may or may not get to this before you leave California.

Big picture goal: Understand how what we did is different than what others (Chauhan, Choudhury, (Rebull/Johnson)) did with the IRAC (IRAC+MIPS) data to find young stars.

More specific shorter term goals: Knowing what you do now, go back and reread Chauhan et al. and Choudhury et al. Do a detailed comparison of our method for finding young stars and that from those two papers.

Relevant links: How can I find out what scientists already know about a particular astronomy topic or object? and I'm ready to go on to the "Advanced" Literature Searching section and C-CWEL Journal Club.

Questions for you:

  1. What are the steps (cookbook-style) that Chauhan et al. used to find YSOs?
  2. What were our steps?
  3. How are they different?
  4. Did we recover all of the young stars identified in the literature? Some will not have IR excesses, so those will not be recovered by an IR-based color selection.

Putting this in context a little: Science

Goal: put our work in context with other literature on BRC38 and other star-forming regions from the literature.

How many YSOs with IR excess did we see? How many literature YSOs did not have IR excesses? Do we have any evidence that the YSOs from the literature are not actually YSOs? How many new YSOs did we see? What is the fraction of Class I/flat/II/III? How do those fractions compare to what was found by C-WAYS in BRC 27?

Writing it up!

Goal: We need to write an AAS abstract and then the poster, and if we're lucky, a paper!

We need to include:

  1. How the data were taken.
  2. How the data were reduced.
  3. What the Spitzer properties are of the famous objects, including how the Spitzer observations confirm/refute/resolve/fit in context with other observations from the literature.
  4. What the Spitzer properties are of other sources here, including objects you think are new YSOs (or objects you think are not), and why you think that.
  5. How this region compares to other regions observed with Spitzer.

Take inspiration for other things to include from other Spitzer papers on star-forming regions in the literature.