Tuesday, June 16, 2009


I spent some time talking to Beth comparing what I have to what she got a few years ago. I ended up taking out my chi and sharp cuts--these can always be added in later. According to Beth, everything seems comparable between my single exposure analyses and hers which is good news.

I also madesome improvements on the plots of position versus offset for both bands for both the new .opts and old .opts. Eyeballing them, there's no real dependence on position, but I'll wait for some feedback from Beth on this and perhaps later (tomorrow?) fit a line to this data to see what kind of a relationship there really is.

Continuing on the quest for calibration, I've written some code that uses linfit to fit a line to the zero-point versus color plots for both bands. The color terms are about 0.05 and 0.04 for the g and r bands, respectively, so this is also good news. I'm now going to apply some code that Beth sent to fit this same data a little better. She used fitexy and was able to incorporate the measurement uncertainties. She also iterated the fit, throwing out data that was more than 3 sigmas from the fit. I know for a fact that I have at least one outlier for each band so this will be impotant. So now that I've used linfit to get a general idea that things are sane, I'll use the more robust version to get a better value for the calibration.

In essence, I've plotted true_mag - inst_mag vs. inst_gmag - inst_rmag. So I've fitted a line that will follow the format true_mag = inst_mag + zero point + slope*(inst_gmag - inst_rmag). I know all of these things except the "slope" which is what all this fitting should solve for. All I know is that it should be small.


1a. Meet with Beth at 9 to talk about subtracted images, etc.

1b. Mention the issue of old .opts vs. new .opts. There's not a big difference between the two in the stack images thus far. Can I make a decision to ditch one in favor of the other? That'll cut down on time spent analyzing things. Because there's not large discrepancy between the two, I'm leaning toward the new .opt files since we know that it some ways at least they're better. And they're obviously not causing any major problems. Are there any other results we're waiting on to make this decision?

2. Talk with Dave at 10.

3. DAOphot average stack. Beth expects that we can get another half a magnitude from this. She's currently digging around for the flat-fields and bad pixel masks.

4. More calibration--get Beth's code working to include measurement uncertainties.

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