HG-WELS Resolution Worksheet - Revision history

Rebull: /* Getting started: what sizes do we expect? */

2014-03-31T23:31:50Z

Getting started: what sizes do we expect?

Rebull at 04:28, 11 March 2014

2014-03-11T04:28:06Z

Rebull: /* Pulling it all together */

2014-03-05T17:51:29Z

Pulling it all together

Rebull: /* Finder Chart IRSA tool */

2014-03-05T05:35:00Z

Finder Chart IRSA tool

Rebull: /* Finder Chart IRSA tool */

2014-03-05T05:34:08Z

Finder Chart IRSA tool

Rebull: /* Finder Chart IRSA tool */

2014-03-05T05:33:48Z

Finder Chart IRSA tool

Rebull at 05:33, 5 March 2014

2014-03-05T05:33:26Z

Rebull: /* Finder Chart IRSA tool */

2014-03-05T05:31:35Z

Finder Chart IRSA tool

Rebull: /* Introduction */

2014-03-05T05:26:55Z

Introduction

Rebull: /* Finder Chart IRSA tool */

2014-03-05T05:25:18Z

Finder Chart IRSA tool

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 *'''Q1.4:''' Put our Sun, with a Kuiper Belt, at the distance of Proxima Centauri. What angular size would the Sun be? The Kuiper Belt? In reality, the circumstellar disk surface brightness is much, much fainter than the central star, but for purposes of this example, let's ignore that.  Take the solar radius as 7e5 km and the KB as 6e9 km.
 *'''Q1.5:''' The disk around beta Pictoris is about 1650 AU in radius. What angular size would that be? (Again, though, the brightnesses are so different, in order to see the disk at all, you have to block out the brightness of the central star and integrate for a long time.)
-*'''Q1.5:''' All of our K giants should be farther away than Beta Pictoris. Our test guy, HD 787, has a measured parallax of 5.24 mas. Put a Kuiper Belt around him. What size would it be, ignoring issues of surface brightness and contrast with the star?
+*'''Q1.6:''' All of our K giants should be farther away than Beta Pictoris. Our test guy, HD 787, has a measured parallax of 5.24 mas. Put a Kuiper Belt around him. What size would it be, ignoring issues of surface brightness and contrast with the star?
 Store these numbers away for comparison to your answers to the questions in the later sections. For those of you chomping at the bit -- will we see any disks or rings around our stars using our data?

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 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.
-Technically, to be absolutely correct, because you are calculating distances on a sphere, in order to do this, you need to do spherical trigonometry. This matters because the angle subtended by 1 hour of RA on the celestial equator is much larger than that subtended by 1 hour of RA near the celestial pole. However, over these relatively small distances, it should be mostly fine to simply subtract the RA and Dec to get a reasonable estimate of the size of the pixels BUT WATCH YOUR UNITS because RA by default is in hours:min of time:sec of time, not deg:arcmin:arcsec. It does make a difference, though. See [http://spiff.rit.edu/classes/phys301/lectures/precession/precession.html#sep this excerpt from someone's class notes] with some really nice graphics and explanations of why you need to do this, and how to do it right. (hint: For the distances we'll consider here, you need a cosine of the declination. I won't make you do the full spherical trig for distances more than a degree.) For the ambitious, anticipating skills you'll need downstream from this worksheet, try programming a spreadsheet to do this for you, given two RA,Dec position pairs. '''NB: Be sure to watch your units on the Dec-- some cosine functions want radians, and some take degrees.'''  (Bonus: how much of a difference does it make if you leave out the cos(dec) term? How much does the cos(dec) term matter for one of the other BRCs?)
+Technically, to be absolutely correct, because you are calculating distances on a sphere, in order to do this, you need to do spherical trigonometry. This matters because the angle subtended by 1 hour of RA on the celestial equator is much larger than that subtended by 1 hour of RA near the celestial pole. However, over these relatively small distances, it should be mostly fine to simply subtract the RA and Dec to get a reasonable estimate of the size of the pixels BUT WATCH YOUR UNITS because RA by default is in hours:min of time:sec of time, not deg:arcmin:arcsec. It does make a difference, though. See [http://spiff.rit.edu/classes/phys301/lectures/precession/precession.html#sep this excerpt from someone's class notes] with some really nice graphics and explanations of why you need to do this, and how to do it right. (hint: For the distances we'll consider here, you need a cosine of the declination. I won't make you do the full spherical trig for distances more than a degree.) For the ambitious, anticipating skills you'll need downstream from this worksheet, try programming a spreadsheet to do this for you, given two RA,Dec position pairs. '''NB: Be sure to watch your units on the Dec-- some cosine functions want radians, and some take degrees.'''  (Bonus: how much of a difference does it make if you leave out the cos(dec) term?)
 OK, returning to my question above - 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? Skyview did exactly what you asked it to do, and gave you an image 300 pixels across. What is the native resolution of the DSS image (e.g., what is the size of the pixels you can see, vs the pixels you asked it for [xx degrees over yy pixels])?

← Older revision		Revision as of 17:51, 5 March 2014
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	Recall that '''THE POINT''' of doing this is to start to develop a sense of (1) what resolution to believe from any given telescope (and to what extent you can trust Skyview); and (2) how this changes between telescopes, e.g., IRAS vs. WISE vs. 2MASS resolution and what this means at a gut level. Is this starting to make more sense?		Recall that '''THE POINT''' of doing this is to start to develop a sense of (1) what resolution to believe from any given telescope (and to what extent you can trust Skyview); and (2) how this changes between telescopes, e.g., IRAS vs. WISE vs. 2MASS resolution and what this means at a gut level. Is this starting to make more sense?

		+	Basic questions to be sure you know the answer to:
		+	* How can you get access to data using Skyview? Using FinderChart? When would you use one vs. the other?
		+	* Will we see disks or rings in our data?
		+	* What is the spatial resolution of IRAS? WISE?
		+	* Is is possible that the sources seen as individual with IRAS will break into pieces when viewed with WISE?
		+	* Is there any guarantee that a single source seen with WISE is really a single object?

	=Postscript: Slight improvements are sometimes possible=		=Postscript: Slight improvements are sometimes possible=

@@ Line 143: / Line 143: @@
 FinderChart also lets you retrieve and overlay catalogs. With IRAS 03275+3020 = 3h30m35.90s +30d30m24.0s loaded in, go and get the IRAS Point Source Catalog (PSC) and overlay it - you probably want to change the search parameters such that it doesn't get sources over the whole 20x20arcmin patch, but more like 5 arcmin. The Faint Source Catalog (FSC) is exactly that - a fainter reprocessing of the IRAS images. (IRAS was the only thing we had for a really long time...) Go and get that one too.  How well does it match sources in the IRAS image? The WISE image? (Kind of amazing to me anyway that it did as well as it did!) Can you find an IRAS source that broke into pieces with WISE? You can do the same thing for WISE and 2MASS catalogs, but there are a LOT more sources (which you can see in the images). Downstream, we will use Gator to request catalog entries around each source in our source list all at once. We will learn what all the columns mean in the catalogs, and decide which sources to keep and believe, and which to not believe. The IRAS PSC sources in this region are bright at different IRAS bands, and are believable (or not) flux densities at different bands - you need to learn about the data quality flags to understand which sources the catalog itself believes are real.
-You may also wish to try the 3rd example above: 3h41m58.60s +31d48m21.0s - there should be only one PSC source at this location, and it breaks into many pieces with WISE.
+You may also wish to try the 3rd example above: 3h41m58.60s +31d48m21.0s - there should be only one PSC source at this location, and it breaks into many pieces with WISE. THIS is the kind of thing I'm worried about with the sources in our target list!
 =Pulling it all together=

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 [http://irsa.ipac.caltech.edu/applications/finderchart/ FinderChart] is a web-based tool housed at IRSA. It is, in some ways, a very much pared down version of Skyview, which only serves relatively tiny images from only a few surveys... but only in native pixel resolution.  I use it far more often than Skyview, in general, because I am very often investigating the properties of individual sources, or trying to understand what I see in Spitzer or WISE. These are also guaranteed to be unresampled images, so they are OK for doing detailed science. On the other hand, we shouldn't need to do photometry on 2MASS or WISE or even Spitzer images, but it is still useful to, e.g., not worry about seams between tiles.
-Go get a 20 arcminute patch of sky using FinderChart of HD 787. Ask it for DSS, 2MASS, WISE, and IRAS. (The default is to look for SDSS too, but there isn't any Sloan coverage.) When it brings up the results, what it is showing you are the actual FITS images, not jpegs or pngs. Click on the toolbar icon to bring up the toolbox full of things you can do to/with the images, either all at once, or individually. As shown, they all cover the same patch of sky; zooming in on one zooms them all in. Changing the color table is useful for telling if the image is slightly asymmetric (implying a barely resolved companion) or saturated or other things. Click on "prepare download" to get the FITS (or the pngs, or a pdf, or the html for that matter). Do it again for IRAS 03275+3020 = 3h30m35.90s +30d30m24.0s. For one of them, check and convince yourself that these are native pixel scale.  Load them into ds9 with one of your other images from Q2.5 above. Use ds9's tiles view and snap them all to the WCS coordinates.
+Go get a 20 arcminute patch of sky using FinderChart of HD 787. Ask it for DSS, 2MASS, WISE, and IRAS. (The default is to look for SDSS too, but there isn't any Sloan coverage.) When it brings up the results, what it is showing you are the actual FITS images, not jpegs or pngs. Click on the toolbar icon to bring up the toolbox full of things you can do to/with the images, either all at once, or individually. As shown, they all cover the same patch of sky; zooming in on one zooms them all in. Changing the color table is useful for telling if the image is slightly asymmetric (implying a barely resolved companion) or saturated or other things. Click on "prepare download" to get the FITS (or the pngs, or a pdf, or the html for that matter). Do it again for IRAS 03275+3020 = 3h30m35.90s +30d30m24.0s. For one of them, check and convince yourself that these are native pixel scale.  Load them into ds9 with one of your other images from above. Use ds9's tiles view and snap them all to the WCS coordinates.
 FinderChart also lets you retrieve and overlay catalogs. With IRAS 03275+3020 = 3h30m35.90s +30d30m24.0s loaded in, go and get the IRAS Point Source Catalog (PSC) and overlay it - you probably want to change the search parameters such that it doesn't get sources over the whole 20x20arcmin patch, but more like 5 arcmin. The Faint Source Catalog (FSC) is exactly that - a fainter reprocessing of the IRAS images. (IRAS was the only thing we had for a really long time...) Go and get that one too.  How well does it match sources in the IRAS image? The WISE image? (Kind of amazing to me anyway that it did as well as it did!) Can you find an IRAS source that broke into pieces with WISE? You can do the same thing for WISE and 2MASS catalogs, but there are a LOT more sources (which you can see in the images). Downstream, we will use Gator to request catalog entries around each source in our source list all at once. We will learn what all the columns mean in the catalogs, and decide which sources to keep and believe, and which to not believe. The IRAS PSC sources in this region are bright at different IRAS bands, and are believable (or not) flux densities at different bands - you need to learn about the data quality flags to understand which sources the catalog itself believes are real.

@@ Line 144: / Line 144: @@
 You may also wish to try the 3rd example above: 3h41m58.60s +31d48m21.0s - there should be only one PSC source at this location, and it breaks into many pieces with WISE.
 =Pulling it all together=
-Recall that '''THE POINT''' of doing this is to start to develop a sense of (1) what resolution to believe from any given telescope (and to what extent you can trust Skyview); and (2) how this changes between telescopes, e.g., IRAS vs. WISE vs. Spitzer vs. 2MASS resolution and what this means at a gut level.  Is this starting to make more sense?
+Recall that '''THE POINT''' of doing this is to start to develop a sense of (1) what resolution to believe from any given telescope (and to what extent you can trust Skyview); and (2) how this changes between telescopes, e.g., IRAS vs. WISE vs. 2MASS resolution and what this means at a gut level.  Is this starting to make more sense?

@@ Line 141: / Line 141: @@
 Go get a 20 arcminute patch of sky using FinderChart of HD 787. Ask it for DSS, 2MASS, WISE, and IRAS. (The default is to look for SDSS too, but there isn't any Sloan coverage.) When it brings up the results, what it is showing you are the actual FITS images, not jpegs or pngs. Click on the toolbar icon to bring up the toolbox full of things you can do to/with the images, either all at once, or individually. As shown, they all cover the same patch of sky; zooming in on one zooms them all in. Changing the color table is useful for telling if the image is slightly asymmetric (implying a barely resolved companion) or saturated or other things. Click on "prepare download" to get the FITS (or the pngs, or a pdf, or the html for that matter). Do it again for IRAS 03275+3020 = 3h30m35.90s +30d30m24.0s. For one of them, check and convince yourself that these are native pixel scale.  Load them into ds9 with one of your other images from Q2.5 above. Use ds9's tiles view and snap them all to the WCS coordinates.
-'''Q4.1 :''' FinderChart also lets you retrieve and overlay catalogs. With IRAS 03275+3020 = 3h30m35.90s +30d30m24.0s loaded in, go and get the IRAS Point Source Catalog (PSC) and overlay it - you probably want to change the search parameters such that it doesn't get sources over the whole 20x20arcmin patch, but more like 5 arcmin. The Faint Source Catalog (FSC) is exactly that - a fainter reprocessing of the IRAS images. (IRAS was the only thing we had for a really long time...) Go and get that one too.  How well does it match sources in the IRAS image? The WISE image? (Kind of amazing to me anyway that it did as well as it did!) Can you find an IRAS source that broke into pieces with WISE? You can do the same thing for WISE and 2MASS, but there are a LOT more sources (which you can see in the images).
+'''Q4.1 :''' FinderChart also lets you retrieve and overlay catalogs. With IRAS 03275+3020 = 3h30m35.90s +30d30m24.0s loaded in, go and get the IRAS Point Source Catalog (PSC) and overlay it - you probably want to change the search parameters such that it doesn't get sources over the whole 20x20arcmin patch, but more like 5 arcmin. The Faint Source Catalog (FSC) is exactly that - a fainter reprocessing of the IRAS images. (IRAS was the only thing we had for a really long time...) Go and get that one too.  How well does it match sources in the IRAS image? The WISE image? (Kind of amazing to me anyway that it did as well as it did!) Can you find an IRAS source that broke into pieces with WISE? You can do the same thing for WISE and 2MASS catalogs, but there are a LOT more sources (which you can see in the images). Downstream, we will use Gator to request catalog entries around each source in our source list all at once. We will learn what all the columns mean in the catalogs, and decide which sources to keep and believe, and which to not believe. The IRAS PSC sources in this region are bright at different IRAS bands, and are believable (or not) flux densities at different bands - you need to learn about the data quality flags to understand which sources the catalog itself believes are real.
-Downstream, we will use Gator to request catalog entries around each source in our source list all at once. We will learn what all the columns mean in the catalogs, and decide which sources to keep and believe, and which to not believe.
+You may also wish to try the 3rd example above: 3h41m58.60s +31d48m21.0s - there should be only one PSC source at this location, and it breaks into many pieces with WISE.
 =The role of Spitzer data=

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 *The first object in the de la Reza list is HD 787. We can use that as an example position.
 *Another example position we will use is IRAS 03275+3020 = 3h30m35.90s +30d30m24.0s - this is not on our list of K giants, but it will demonstrate some of the issues we may encounter.
-*Finally, IRAS 03388+3139 = 3h41m58.60s +31d48m21.0s is another, less good example. :)
+*Finally, IRAS 03388+3139 = 3h41m58.60s +31d48m21.0s is another, totally optional, less good example. :)
 Please keep track of your answers to these questions in your own notes, not on the wiki! I want you to come up with the answer while not being biased (yet) by what other people get. We will compare answers on the phone during a regular telecon.