Fwd: PHOT Question
Mike Fitzpatrick wrote on Dec 06, 2007
I'd like to run phot in batch mode on a few hundred CCD images of the same field, taken on different nights. What I would like to measure is the brightness of a quasar and the brightness of four or five comparison stars in the field. I want to specify the coordinates in RA and DEC instead of pixel x,y because the location of the stars changes by too many pixels from image to image and night to night. What input parameters do I need to set in phot that will tell the program the stars.coo file has RA and DEC and not x and y? I've run phot successfully using x and y inputs from daofind. Here's the type of file I want to use as input (no problem changing to degrees, of course):
#stars in 3C454.3 field
22 53 00.0 +16 09 53
22 53 55.3 + 16 07 08
Thanks in advance for any help you can give.
#stars in 3C454.3 field
22 53 00.0 +16 09 53
22 53 55.3 + 16 07 08
Thanks in advance for any help you can give.
Francisco Valdes wrote on Dec 06, 2007
Hi,
You set the "wcsin" and "wcsout" parameters to "world". This can be done in the phot parameters or, indirectly, in the package parameters of the same name. This requires that the images have a world coordinate system that IRAF understands (the most common FITS WCS systems such as TAN).
The coordinates then have to be in degrees for both RA and DEC and must be either in decimal degrees or "xx:xx:xx.xx..."; i.e. colon separated and not space separated. Another point is that the columns need to be in the order in which the image WCS is defined; i.e. if CTYPE1='DEC-TAN' and CTYPE2='RA--TAN' then the columns have to be dec and RA respectively.
As an alternative, probably within a script, you could use the task WCSCTRAN to convert the RA/DEC columns to pixels coordinates for each image. The advantage of this is that this task can be told that RA is in hours if desired.
Yours,
Frank Valdes
You set the "wcsin" and "wcsout" parameters to "world". This can be done in the phot parameters or, indirectly, in the package parameters of the same name. This requires that the images have a world coordinate system that IRAF understands (the most common FITS WCS systems such as TAN).
The coordinates then have to be in degrees for both RA and DEC and must be either in decimal degrees or "xx:xx:xx.xx..."; i.e. colon separated and not space separated. Another point is that the columns need to be in the order in which the image WCS is defined; i.e. if CTYPE1='DEC-TAN' and CTYPE2='RA--TAN' then the columns have to be dec and RA respectively.
As an alternative, probably within a script, you could use the task WCSCTRAN to convert the RA/DEC columns to pixels coordinates for each image. The advantage of this is that this task can be told that RA is in hours if desired.
Yours,
Frank Valdes
Last post on Dec 06, 2007