[Aavso-photometry] Re: [CCD-astrometry-photometry] WCS Starlists in IRAF

[Michael Koppelman]

I think the way I did this was something like this:

1. Use wsctools to put WCS info in header.
2. Use daofind to find stars in X/Y coordinates.
3. Use the wcs command 'xy2sky' on the file created in #2 to create a 
file with X/Y to RA/Dec mapping.
4. Do photometry using X/Y coordinates.
5. Use a perl script to look up the RA/Dec for each star in the 
photometry file from the file in #3.

This sounds like your 2nd approach below.

I was hoping that the IRAF phot task could take a coordinates file in 
RA/Dec rather than pixels but I could not get it to work.

Michael

On Jun 29, 2004, at 12:55 PM, Chuck Pullen wrote:

> 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
>
>
>
> ------------------------ Yahoo! Groups Sponsor --------------------~-->
> Yahoo! Domains - Claim yours for only $14.70
> http://us.click.yahoo.com/Z1wmxD/DREIAA/yQLSAA/1.XolB/TM
> --------------------------------------------------------------------~->
>
> ------------------------------------------------------------------
> Group page: 
> http://groups.yahoo.com/group/CCD-astrometry-photometry/For any 
> problem or suggestion, please contact the group moderator at:
> CCD-astrometry-photometry-owner at yahoogroups.com
>
> lem or suggestion, please contact the group moderator at:
> CCD-astrometry-photometry-owner at yahoogroups.com
>
>
> Yahoo! Groups Links
>
> <*> To visit your group on the web, go to:
>      http://groups.yahoo.com/group/CCD-astrometry-photometry/
>
> <*> To unsubscribe from this group, send an email to:
>      CCD-astrometry-photometry-unsubscribe at yahoogroups.com
>
> <*> Your use of Yahoo! Groups is subject to:
>      http://docs.yahoo.com/info/terms/
>
>