Wednesday, June 3, 2009


I started out wanting to fix the distortion maps so that it would show all 8 chips. In order to do so I had to scamp the MEF files. So I started by sextractor-ing the MEF files so that I could get the catalog files needed to input into scamp. I was concerned about inputting the gain here because before I had been doing it on the command line for each chip. But now that each chip was in a different extension of the MEF files for each exposure, that was an issue. I talked with Beth and she suggested that it didn't matter too much for a similar reason to why we can use a constant gain and read noise in DAOphot. So I took the median of the gains of each chip and used that as the value in the .sex configuration file:

sex gain= 2.75

I then used the output catalogs from sextractor to run scamp and discovered that the distortion files were in fact showing all 8 chips! Victory!

Seeing that scamp was playing nicely, I went on to swarp the MEFs together. My concern about gain issues was further alleviated by the fact that swarp was getting the proper gains out of the image headers. I then took a look at the stacked image to make sure it looked alright. There's nothing obvious that stands out--the stack looks as good as it did before. I'll check again after DAOphot star subtracts.

After that I added the constant sky into the new 10-exp stack, using the same median value that I calculated before.

3. Then I ran DAOphot and checked again to make sure I have the best analytic model possible.

Model # ........ Avg Chi^2

This time it looks like the close race is between 6 and 7, but 6 wins out by a little bit. I DAOphoted again and got the average chi for #6 to be 0.0139 and the average of #7 to be 0.0140. The slight changes are presumably because of minor discrepancies in how I was manually selecting the psf stars. But #6 still wins so that's what I'll stick with.

In the process of DAOphoting I discovered another parameter that's neither in the manual or in our daophot.opt file, but apparently is in the default daophot.opt. Keyword is "USE SATURATED PSF STARS" and it's currently set to 0.0. I'm willing to bet 0= "No" and move on with my life.

I overplotted the SDSS stars once again to make sure that was still looking consistent and see if it looked any better than before. I'm still concerned by a few places where SDSS shows a star and nothing at all appears in the stack, even before star subtraction. But other than that, things look fine.

I then re-did the 7-exp g and r stack using MEFs and re-did all of the DAOphoting and Allstaring there so that I can come up with the CMD.


Come up with a good CMD and go over CMD calibration with Beth.

No comments:

Post a Comment