[Aavso-photometry] WCS Starlists in IRAF

[Chuck Pullen]

If you got this twice, my apologies in advance.  I realize that these two 
lists are not 100% complementary.


>Date: Tue, 29 Jun 2004 10:55:28 -0700
>To: CCD-astrometry-photometry2
>From: Chuck Pullen <cpullen at pacsafe.com>
>Subject: WCS Starlists in IRAF
>Bcc: Aaron Price <aaronp at onceler.org>
>
>I know some of the folks on this list use IRAF, so I will give this issue 
>a try here.
>
>
>ISSUE
>
>Lets say I have a stack of a nights images consisting of 100 images of the 
>same field.  These images have been astrometrically solved using Bob 
>Denny's pinpoint, with the WCS info placed in the Header.  While the 
>images are of the same field, there is up to an arc minute drift over an 
>entire nights run do to use of a guide scope, flexure, etc.  So, I can't 
>just designate the pixel coordinates of my variable and comp star(s) for 
>the entire stack and just use those for a PHOT run.
>
>I want to do photometry on lets say just two stars in the field.  I have 
>accurate RA and Dec for these two objects.  What I need to do is find a 
>way to have IRAF make me a coordinate list for each image in physical 
>pixel values for these two stars based on their RA and Dec.  Sounds 
>simple, but it's not.
>
>WHAT I'VE TRIED
>
>First Approach: I can make that coordinate file for the entire stack of 
>images using WCSCTRAN and the RA and Dec of the two stars of 
>interest.  However, for reasons I don't understand, I get massive 
>multiples on the photometry if I use that file to input into the PHOT 
>task.  If there are 100 images in the stack, that coordinate list will run 
>each image in the stack 100 times! There must be a better way.
>
>A Second Approach is to use DAOFIND to extract most or all of the stars on 
>each image then run PHOT on that list.  Easy.  Now, though, I have a file 
>in pixel values for coordinates.  WCSCTRAN needs column numbers in the 
>.par file to find pixel values for converstion to RA and Dec.  The PHOT 
>output files are not linear, that is they contain line breaks or other 
>formatting so I can't figure out what to input for column numbers in the 
>par file for WCSCTRAN.  I can extract the x & y pixel values, the JD, mag, 
>and mag err from that output file using TXDUMP.  However, if I try to 
>convert that file using WCSCTRAN, it has lost it's ability to use the WCS 
>solution from each image so the output is worthless.  I'm not sure that 
>even if I knew how to tell WCSCTRAN how to find the pixel coordinates in 
>the standard PHOT output format, that it would be able to match up to each 
>image's WCS solution.
>
>I'd appreciate any suggestions, and thank you in advance for any thoughts 
>you might have.
>
>As a back up, I'd be happy to take a suggestion (in PERL or maybe AWK) how 
>to simply clean up the redundancy from the file under first 
>approach.  That would at least get me in business.
>
>Thanks!
>
>Chuck Pullen