Monday, June 22, 2009

Things I figured out/did today:

Today has been a hodge podge of trying things to see if there is any indication of where our methods could be going wrong or could be improved.

Took a look at many different versions of the chi versus sharp plots for the weighted stack, single exposure, and median stack in each band. I overplotted green dots that represented those stars that matched between the bands and noticed that these were spread throughout, which was to be expected. I did note that stars in the weighted stack weren't matching to the most extreme stars detected in either bands, while the faintest stars in the single exposure and median stacks did match. This is keeping in mind that the latter two don't go as deep to begin with.

I also grumbled about the bad flat fields for a while. But Beth reminded me that they have already been used (the images were divided by them in the first round of image reduction) so we can't do anything about them. In fact, using them to stack the images now should account for any badness. This is reflected by the fact that our stacked images look fine. And besides, they reflect the chip they were taken from so it's the camera that looks bad, which is important to take into account. It's just unfortunate that Wil1 is centered on worst chip of camera.

I thought briefly that the CMD I was creating from only stars close to Willman 1 was significantly shallower (up to 1 mag) than the CMD with all stars in the field. Beth reminded me that it could be a deceiving because of the huge difference in densities, what with so few stars from the field residing within 5 arcmin of the center of Willman 1. On her suggestion, I followed up by remaking the CMD of the field, btu plotting only a random sample of those stars equal in size to that of the close-up CMD. It would seem that what I was seeing was a result of the high number of stars because this last plot showed about the same depth as the close-up one. Oh well...seems I'll try anything to get to the ever elusive 26th magnitude mark.

I made a 10 exposure r stack to check and see if that could get us any deeper or a better image. I used the same technique as before with weight maps, etc. I also checked the swarped images which, thanks to the weight mapping, look pretty good. After DAOphot'ing, I discovered that the standard deviation of the image is in fact smaller for the 10 exposures than for the 7 exp stack (9.98 as opposed to 10.908--I'd say this is a big enough difference to warrant some interest). DAOphot also found 10,000 more stars from extra three exp (now we're up to 46,000) so I'm hoping that they're not all crap and can contribute to the fainter mags. I checked out the chi and sharp plots and I'd say they add a few tenths of a mag to the 7 exposure weighted image. Considering all these things, I'm going to say that the 10 exposure stack is the way to go. Particularly because bad image quality is what got those three exposures thrown out to begin with and that's no longer an issue.

Still to do/consider (by no means in order of importance):

1. On the calibration code I still need to: bootstrap calibration, find mean, median, variance
2. Use python code to iterate allstar--does this get us any deeper?
3. Should we go back and use the weight maps in sextractor? Could it make a big difference in detecting faint sources from the beginning? I got this idea from reading Dave's Hercules paper this morning. It's a rather handy step-by-step guide of pretty much everything I'm doing.
4. Submit registration/abstract for workshop ASAP.
5. Talk to Dave about images.
6. Fix bug in sharp/chi comparison code.

1 comment:

  1. Gail you are doing so great! Remember, this was data I gave up on improving when I was a postdoc. Although its probably tough to see from where you are right now, both of us have been learning so much. I couldn't be more happy with how much I've learned from you and this research.