Friday, June 5, 2009

Brief Update


Talked with Dave this morning about diagnosing the CMD problems I'm having. He taught me some tricks to use with ds9--WCS matching and some region files stuff. He also sent me some python code to match stars between the two bands.

I didn't get to the but that'll be first up for Monday if not before. I wrote some code to make my own region files and overplotted them onto the images in ds9 and nothing looked wrong. I also checked to be sure that the psfs were spread pretty evenly over th entire image. It looks as if they are, though there's a suspicious lack of psfs in the center of the image.

I also made a histogram of the match distances spherematch is finding when I match stars between the catalogs that way. I'm suspicious of how many stars spherematch is finding--about 600 match to within 1 arcsecond out of ~30,000 stars in each catalog. Hopefully messing with will shed some light on this problem.

Other than that I WCS matched the three stacks in ds9 and discovered some *gasp* wiggling in the location of stars. Incidentally, the g7 and g10 stacks appear to be the furthest off.Talked with Beth about this briefly. Doesn't seem to be a header issue because I feel that there would be a greater discrepancy, though I'll investigate this further on Monday. Also seems like the stars would be elliptical if it was a scamp issue.

The stars in the r7 stack also look a lot bigger than the others. Beth attributed this to a different FWHM than the g-band, which makes me concerned about the fact that I used the same FWHM for all my DAOphoting. But Beth doesn't think that a FWHM that was a little off should cause a big problem.

Both Beth and I seem to be out of ideas at the moment, so the weekend will be a good time to think some more. Waiting until Dave gives me info on how to give him my images via FTP so that he can offer an opinion.

1 comment:

  1. Agree that should be on the top of the list. It would be dreadful and unexpected if the swarp header somehow didn't play that nice with adxy. This would be surprising, because I've used adxy plus position_match on the .als output from photometering swarped images from the MMT Megacam instrument, and it worked well.