iraf.net

Hi all, I'm trying to do differential photometry on some 500 frames. I used daophot package phot task to do the aperture photometry and get the results in mag.1 files. Files contain the magnitudes of both the variable and the comparison stars. Now the problem is that, there are other stars and i can not get the differential magnitudes which are the differences between two magnitudes on different lines in the file.Now, is there anyone who can tell me if i could it with txdump by some trick? or would i have to use some other external package written for differential photometry like vaphot (though i couldn't reach the ftp site where it is)?Thanks in advance,
Ozgur Basturk
Ankara University

Hi thereI use txdump to dump the individual stars to text files and then use matlab scripts to do the differential photometry correction and binning if need be. To get to the point: I would also like to be interested in a method to use IRAF to do the differential phot part as we already have a custom photometry pipeline/package that we use, and would like to add a differential photometry task to it!!!!Regards
Pat

Hi Pat,I couldn't get individual stars to seperate files so that i can do mathematical operations (just subtraction actually ). The problem is that the variable and the comparison are somehow close both in position on the CCD and in magnitude, that's why i could not define a condition for txdump. There are two other stars which are almost at the same magnitude with my stars so the id's that phot task gave to them change from frame to frame.Is there a way to get each of my star's magnitudes to seperate files (without transferring to WCS)? By the way, is there anyone who use xapphot in guiapps package?Thanks in advance
Ozgur Basturk
Ankara University

Hi OzgurThe method that we use is to first align the data frames, then use either daophot's daofind task to find the stars in the field, or use ds9 to set up a coordinate file. We then pass that .coo file to the phot task for photometry measurement. In this way u make sure that the star id's should be the same throughout the exercise.U can then use txdump with a extended expression to define the stars that it should dump. We usually dump it by first looking at the starid, then the y,x coordinates, then the magnitudes.Hope this helps.Regards
Pat

Hi Pat,Thanks for the advice. I really don't like imalign task much. But when i aligned the images by imal2 task in the vaphot external package written for differential photometry, the whole problem is solved.I recommend vaphot task and other scripts distributed with it for all who wants to do differential photometry. I checked my results with other eduction softwares and saw that they were quite alright. Thanks for your help
Ozgur

would anyone mind pointing me towards the download location for vaphot?

found it, thanks for looking.

See ftp://ftp.iac.es/tepstuff/tep_dist/