C-CWEL Resolution Worksheet - Revision history

Rebull at 18:02, 17 June 2013

2013-06-17T18:02:39Z

Rebull at 03:13, 6 June 2013

2013-06-06T03:13:31Z

Rebull at 03:00, 6 June 2013

2013-06-06T03:00:53Z

Rebull at 22:46, 5 June 2013

2013-06-05T22:46:26Z

Rebull: /* Exploring POSS images */

2013-06-05T22:44:30Z

Exploring POSS images

Rebull at 16:33, 5 June 2013

2013-06-05T16:33:31Z

Rebull at 16:29, 5 June 2013

2013-06-05T16:29:51Z

Rebull: /* Exploring POSS images */

2013-05-29T23:54:15Z

Exploring POSS images

Rebull: /* The role of Spitzer data */

2013-05-22T21:43:08Z

The role of Spitzer data

Rebull: /* The role of Spitzer data */

2013-05-22T21:35:51Z

The role of Spitzer data

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 Go and obtain WISE images in native pixel resolution of the central region for BRC 38 over an area comparable to the Spitzer observations, ~5 arcmin on a side in the center. You should be able to do this via either the [http://irsa.ipac.caltech.edu/applications/finderchart/ FinderChart] tool or the [http://irsa.ipac.caltech.edu/applications/wise/ WISE Image Server] itself.
-Go and get the Spitzer IRAC observations of BRC 38 -- you can get them directly from the [http://sha.ipac.caltech.edu/applications/Spitzer/SHA/ Spitzer Heritage Archive] database (it looks VERY similar to FinderChart, no? :) ), or I will put them on the web for you. (for at least the next week or so, they will be [http://sha.ipac.caltech.edu/applications/Spitzer/SHA/servlet/Download?file=%24%7Bstage%7D%2Fbid__69241097845__shaapp1_0.zip&return=tgt-2-selected_AORs.zip&log=true&track=true here] and you want the *maic.fits files; the IRAC data will be in a directory that has four channel subdirectories, and the MIPS data will be in a directory that has three channel subdirectories.)
+Go and get the Spitzer IRAC observations of BRC 38 -- you can get them directly from the [http://sha.ipac.caltech.edu/applications/Spitzer/SHA/ Spitzer Heritage Archive] database (it looks VERY similar to FinderChart, no? :) ), or I will put them on the web for you. (for at least the next week or so STARTING JUNE 17, they will be [http://sha.ipac.caltech.edu/applications/Spitzer/SHA/servlet/Download?file=%24%7Bstage%7D%2Fbid__71492002601__shaapp2_0.zip&return=tgt-2-selected_AORs.zip&log=true&track=true here] and you want the *maic.fits files; the IRAC data will be in a directory that has four channel subdirectories, and the MIPS data will be in a directory that has three channel subdirectories.)
 '''Q4.1 :''' The two channels that match the best (e.g., where legitimate astrophysical changes are least likely) are W1 and I1 (3.4 and 3.6 um) and W2 and I2 (4.6 and 4.5 um). This region is complicated due to the bright nebulosity, so you will most likely have to not just align the images but fuss with the stretches of the images individually to compare the images and match structures and sources between the views. Which view of the region has more point sources (W1 or I1? W2 or I2?) Can you find a source in WISE that breaks into pieces when viewed with IRAC?

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	In any case, pick any of the images as primary, and go to the 'frame' menu at the top; go down to "match", pick "frame" again, and then pick "WCS". That means, "align all the images I have loaded in ds9 to be North up, all on the same spatial scale as the image I have selected when I initiate this command." (WCS stands for world coordinate system, meaning that there is information about the ra, dec, and mapping of pixels to ra and dec in the FITS header. ds9 and many other tools are capable of reading that information and translating it in real time to ra and dec under your mouse as you move.) What is the area covered by your image from IRAS (in square degrees!)? WISE? 2MASS? POSS?		In any case, pick any of the images as primary, and go to the 'frame' menu at the top; go down to "match", pick "frame" again, and then pick "WCS". That means, "align all the images I have loaded in ds9 to be North up, all on the same spatial scale as the image I have selected when I initiate this command." (WCS stands for world coordinate system, meaning that there is information about the ra, dec, and mapping of pixels to ra and dec in the FITS header. ds9 and many other tools are capable of reading that information and translating it in real time to ra and dec under your mouse as you move.) What is the area covered by your image from IRAS (in square degrees!)? WISE? 2MASS? POSS?
		+
		+	How big is the 'resolution element' here, for each of these channels?

	'''Q2.4 :''' For a laugh -- go back and try COBE too, though you will probably NOT want native pixel resolution for that; ask it to get you the same area as your IRAS image. How big are the COBE pixels in arcseconds/arcminutes/degrees?		'''Q2.4 :''' For a laugh -- go back and try COBE too, though you will probably NOT want native pixel resolution for that; ask it to get you the same area as your IRAS image. How big are the COBE pixels in arcseconds/arcminutes/degrees?

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 '''Q2.1 :''' Use Skyview to get an 'orientation-level' IRAS image, e.g., the same size as the big POSS above that was ~5 degrees. Some of the choices will be "IRIS" instead of "IRAS" - IRIS refers to a more recent reprocessing of the IRAS data. For these purposes, you can use either one. What are the available bandpasses (and wavelengths)? (Hint: you may need to look beyond Skyview.)  Look for any corresponding features between POSS and IRAS. We will come back to the physics and astrophysics of what is bright/dark in which bands and why, but for now, just convince yourself you have, indeed, obtained the same chunk of sky, covering the same region, and make a note of the differences for later consideration. How big is the 'resolution element' here? How big, typically, are the point sources? Check this in each bandpass. Is it the same, or does it change with wavelength?
-'''Q2.2 :''' OK, now go retrieve a smaller IRAS image, a degree on a side. Get the same area on the sky but in WISE and 2MASS. What are the wavelengths that are available for each of these missions? Try requesting the images "all at once" to see the impact of using the same parameters for each Skyview request.  You will probably find it easier to retrieve the images individually to get the resolutions right! :)  How big is the 'resolution element' here? How big are the pixels? How big, typically, are the point sources? Do your answers to those questions change when the wavelength changes (e.g., are these properties a function of wavelength)?  We are starting to go into the regime where the resolution is not set by seeing (for the space missions in particular!) but more by the wavelength of observation and the diameter of the telescope. See the introduction to the [[Resolution]] page for more on some of this.
+'''Q2.2 :''' OK, now go retrieve a smaller IRAS image, a degree on a side. Get the same area on the sky but in WISE and 2MASS. What are the wavelengths that are available for each of these missions? Try requesting the images "all at once" to see the impact of using the same parameters for each Skyview request.  How big is the 'resolution element' here? How big are the pixels? How big, typically, are the point sources? Do your answers to those questions change when the wavelength changes (e.g., are these properties a function of wavelength)?  We are starting to go into the regime where the resolution is not set by seeing (for the space missions in particular!) but more by the wavelength of observation and the diameter of the telescope, but at this point, the number of pixels and native px resolution is mattering too. See the introduction to the [[Resolution]] page for more on some of this.
 '''Q2.3 :''' Go get a 300 px native resolution image for each band (IRAS, WISE if you can, 2MASS if you can, and POSS). What areas on the sky did they each cover? How many degrees/arcmin/arcsec per pixel are they? How does this compare to POSS? In order to quickly get a gut-level understanding of this, you can stack them up in ds9. Load them all into ds9.  In order to do this, either use the command line (ds9 *fits) or start ds9, then do file/open and find the first image; do frame/new then file/open and load the second image, etc. If you used the command line trick, you will load all the images into individual tiles, in alphabetical order (which is most likely not wavelength order!). If you did them one-by-one, you will have them virtually in a stack, in the order you loaded them. To see all of them at once, click on 'frame' then 'tile.' To get it back to one at a time (in a virtual stack), pick 'single.' To scroll through the whole stack, pick 'next' or 'previous'. You can change the ordering - explore the menu options on the top "Frame" menu.  In the 'single' frame case, the image you are looking at is the active one; in the 'tile' view, the one with the blue outline is the active one. Click on the tile to make it the active one. You may occasionally leave behind a green circle; this is a "region", and they are ultimately very helpful, but at this point, often very annoying. To make it go away, pick it, and hit backspace or delete on your keyboard.

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 *OPTION 3 - You can also do this by hand. Note that as you move your mouse around on the image in ds9, it will give you an updated readout of the ra and dec in the top. You can change this from hh:mm:ss ddd:mm:ss format to decimal degrees for both ra and dec by picking from the "wcs" menu at the top, either 'degrees' or 'sexagesimal'. Make a note of the RA/Dec of the corners of an example pixel and calculate the distance along the sides of a pixel as you see it in the image (as opposed to that in the FITS header). (Yes, the pixels will be irregular; see if you can find a typical pixel in the image.)
-*OPTION 4 - You can also do this using the brand new [http://irsa.ipac.caltech.edu/fftools/app.html IRSA Viewer] -- you can overlay tools including a distance ruler.
+*OPTION 4 - You can also do this using the brand new [http://irsa.ipac.caltech.edu/fftools/app.html IRSA Viewer] -- you can upload images from disk and then overlay tools including a distance ruler.
 No mater how you choose to do this, WATCH YOUR UNITS. RA by default is in hours, not degrees. Dec by default IS in degrees.

← Older revision		Revision as of 22:44, 5 June 2013
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	*OPTION 3 - You can also do this by hand. Note that as you move your mouse around on the image in ds9, it will give you an updated readout of the ra and dec in the top. You can change this from hh:mm:ss ddd:mm:ss format to decimal degrees for both ra and dec by picking from the "wcs" menu at the top, either 'degrees' or 'sexagesimal'. Make a note of the RA/Dec of the corners of an example pixel and calculate the distance along the sides of a pixel as you see it in the image (as opposed to that in the FITS header). (Yes, the pixels will be irregular; see if you can find a typical pixel in the image.)		*OPTION 3 - You can also do this by hand. Note that as you move your mouse around on the image in ds9, it will give you an updated readout of the ra and dec in the top. You can change this from hh:mm:ss ddd:mm:ss format to decimal degrees for both ra and dec by picking from the "wcs" menu at the top, either 'degrees' or 'sexagesimal'. Make a note of the RA/Dec of the corners of an example pixel and calculate the distance along the sides of a pixel as you see it in the image (as opposed to that in the FITS header). (Yes, the pixels will be irregular; see if you can find a typical pixel in the image.)
		+
		+	*OPTION 4 - You can also do this using the brand new [http://irsa.ipac.caltech.edu/fftools/app.html IRSA Viewer] -- you can overlay tools including a distance ruler.

	No mater how you choose to do this, WATCH YOUR UNITS. RA by default is in hours, not degrees. Dec by default IS in degrees.		No mater how you choose to do this, WATCH YOUR UNITS. RA by default is in hours, not degrees. Dec by default IS in degrees.

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 So, what this means is: '''any time you are doing science''', whether that is using your eye to see small details in the image, or measuring distances, or doing photometry, '''you always want to be using the FITS file''', ''never'' a JPG, PNG, or GIF.
-Therefore, you need software capable of reading FITS files.  There is some information on using a variety of packages [[How_can_I_make_a_color_composite_image_using_Spitzer_and/or_other_data%3F | here]], but you might as well start to get comfortable with using [http://hea-www.harvard.edu/RD/ds9/ ds9], since that's what we will be using later on in the project. It's free, and available for just about any platform. There are at least 2 tutorials on using ds9 developed by NITARP students on the wiki for doing some specific things - search in the wiki on ds9 - and more from the rest of the web, including some listed at the bottom of [[How_can_I_make_a_color_composite_image_using_Spitzer_and/or_other_data%3F |this page]]. Also, ds9 was the topic of a tutorial in [[NITARP tutorials]].
+Therefore, you need software capable of reading FITS files.  There is some information on using a variety of packages [[How_can_I_make_a_color_composite_image_using_Spitzer_and/or_other_data%3F | here]], but you might as well start to get comfortable with using [http://hea-www.harvard.edu/RD/ds9/ ds9], since that's what we will be using later on in the project. It's free, and available for just about any platform. There are at least 2 tutorials on using ds9 developed by NITARP students on the wiki for doing some specific things - search in the wiki on ds9 - and more from the rest of the web, including some listed at the bottom of [[How_can_I_make_a_color_composite_image_using_Spitzer_and/or_other_data%3F |this page]]. Also, ds9 was the topic of a tutorial in [http://nitarp.ipac.caltech.edu/resource/8 NITARP tutorials].
 In Skyview, you can ask for more than one survey at the same time, but it uses the same 'common options' you specify on the query page. To select more than one that are not adjacent, hold down the command key while clicking. (That is, at least, on a mac. Your mileage may vary.)

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 For a general introduction, please start with the main text already on the wiki for [[Resolution]]. Please also look at the examples lower on that page, but you don't need to actually do the one that suggests that you go download data, etc.  The skills you might have gained from that specific example will be stuff that we will either do as part of this worksheet, or as part of our Summer visit.
-We will be primarily using [http://skyview.gsfc.nasa.gov/ Goddard's Skyview] to retrieve FITS images for this worksheet. You need a FITS viewer too, I suggest you use DS9 which you can download here: [http://hea-www.harvard.edu/RD/ds9/ DS9]. (see FITS explanation below). Also, ds9 was the topic of a tutorial in [[NITARP tutorials]].
+We will be primarily using [http://skyview.gsfc.nasa.gov/ Goddard's Skyview] to retrieve FITS images for this worksheet. You need a FITS viewer too, I suggest you use DS9 which you can download here: [http://hea-www.harvard.edu/RD/ds9/ DS9]. (see FITS explanation below). Also, ds9 was the topic of a tutorial in [http://nitarp.ipac.caltech.edu/resource/8 NITARP tutorials].
 The questions below are mostly designed to result in a number or a few numbers so that we can more easily compare results. Some of the questions are more open-ended, where we will all need to discuss results.  I suggest we all do BRC 38 at least initially. If you finish doing this for BRC 38, and you want to continue exploration of another target entirely (e.g. your favorite Messier object), please go ahead and do so!

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 '''Q1.4 :''' Go back to Skyview and ask for a much smaller image, 0.1 degree, still with the default 300 px. How big are those pixels -- what do I mean by pixels? What size are the individual pixels in the image as returned to you, and what size are the pixels you can see in the image itself by eye?  You will need to zoom in, probably a lot, and you will need to estimate an average size of the irregular pixels. You will need to find a way to measure distances on images; read on for options.
-OPTION 1 - fortunately, ds9 provides a way to do this, though you may find it clunky. From the menus on the top, select Region/Shape/Ruler. Click on one end of what you want to measure, then move to the other end and click again (or click-and-drag; you may need to experiment to see what your system wants).  A line with arrows will be drawn connecting the two, along with the distance in text and dotted lines completing the triangle.  By default, the distance will be in physical units (pixels of the image you are viewing), but by accessing the region's Get Information panel (top menu: Region/Get information; buttons in the middle of the ds9 screen: Region/Information), you can change both the endpoints and (more usefully) distance units to WCS so that the units will be in degrees, or minutes, or seconds.
+*OPTION 1 - fortunately, ds9 provides a way to do this, though you may find it clunky. From the menus on the top, select Region/Shape/Ruler. Click on one end of what you want to measure, then move to the other end and click again (or click-and-drag; you may need to experiment to see what your system wants).  A line with arrows will be drawn connecting the two, along with the distance in text and dotted lines completing the triangle.  By default, the distance will be in physical units (pixels of the image you are viewing), but by accessing the region's Get Information panel (top menu: Region/Get information; buttons in the middle of the ds9 screen: Region/Information), you can change both the endpoints and (more usefully) distance units to WCS so that the units will be in degrees, or minutes, or seconds.
-OPTION 2 - As our first but certainly not last example of "astronomers using whatever software you are most familiar with to do the job", you are more than welcome to use your own favorite FITS viewer (if yours has an easy way to do this).
+*OPTION 2 - As our first but certainly not last example of "astronomers using whatever software you are most familiar with to do the job", you are more than welcome to use your own favorite FITS viewer (if yours has an easy way to do this).
-OPTION 3 - You can also do this by hand. Note that as you move your mouse around on the image in ds9, it will give you an updated readout of the ra and dec in the top. You can change this from hh:mm:ss ddd:mm:ss format to decimal degrees for both ra and dec by picking from the "wcs" menu at the top, either 'degrees' or 'sexagesimal'. Make a note of the RA/Dec of the corners of an example pixel and calculate the distance along the sides of a pixel as you see it in the image (as opposed to that in the FITS header). (Yes, the pixels will be irregular; see if you can find a typical pixel in the image.)
+*OPTION 3 - You can also do this by hand. Note that as you move your mouse around on the image in ds9, it will give you an updated readout of the ra and dec in the top. You can change this from hh:mm:ss ddd:mm:ss format to decimal degrees for both ra and dec by picking from the "wcs" menu at the top, either 'degrees' or 'sexagesimal'. Make a note of the RA/Dec of the corners of an example pixel and calculate the distance along the sides of a pixel as you see it in the image (as opposed to that in the FITS header). (Yes, the pixels will be irregular; see if you can find a typical pixel in the image.)
 No mater how you choose to do this, WATCH YOUR UNITS. RA by default is in hours, not degrees. Dec by default IS in degrees.

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 Go and get the Spitzer IRAC observations of BRC 38 -- you can get them directly from the [http://sha.ipac.caltech.edu/applications/Spitzer/SHA/ Spitzer Heritage Archive] database (it looks VERY similar to FinderChart, no? :) ), or I will put them on the web for you. (for at least the next week or so, they will be [http://sha.ipac.caltech.edu/applications/Spitzer/SHA/servlet/Download?file=%24%7Bstage%7D%2Fbid__69241097845__shaapp1_0.zip&return=tgt-2-selected_AORs.zip&log=true&track=true here] and you want the *maic.fits files; the IRAC data will be in a directory that has four channel subdirectories, and the MIPS data will be in a directory that has three channel subdirectories.)
-'''Q4.1 :''' The two channels that match the best (e.g., where legitimate astrophysical changes are least likely) are W1 and I1 (3.4 and 3.6 um) and W2 and I2 (4.6 and 4.5 um). This region is complicated due to the bright nebulosity, so you will most likely have to fuss with the stretches of the images individually to compare the images and match structures and sources between the views. Which view of the region has more point sources (W1 or I1? W2 or I2?) Can you find a source in WISE that breaks into pieces when viewed with IRAC?
+'''Q4.1 :''' The two channels that match the best (e.g., where legitimate astrophysical changes are least likely) are W1 and I1 (3.4 and 3.6 um) and W2 and I2 (4.6 and 4.5 um). This region is complicated due to the bright nebulosity, so you will most likely have to not just align the images but fuss with the stretches of the images individually to compare the images and match structures and sources between the views. Which view of the region has more point sources (W1 or I1? W2 or I2?) Can you find a source in WISE that breaks into pieces when viewed with IRAC?
 '''Q4.2 : BONUS''' compare the W4 (22 um) and MIPS-1 (24 um) views. Which view of the region has more point sources? Which sources are the same between the two views?