Changes between Initial Version and Version 1 of GPC_Zero_Points_July09

Timestamp:

Jul 22, 2009, 1:08:43 PM (17 years ago)

Author:

eschlafly@…

Comment:

--

GPC_Zero_Points_July09

@@ +1 @@
+I've compared the 816 processed images from the July 2009 data release to SDSS to get zero points for each image.  For y band I fit y_{PS} - z_{SDSS} versus i_{SDSS}-z_{SDSS} and got a slope of -0.247.  Using this I made a simulated y-band magnitude for each SDSS star as y_{SDSS-sim} = z_{SDSS}-.247*(i_{SDSS}-z_{SDSS}), assuming that stars of zero i-z color should have zero z-y color.  I used the resulting simulated y-band magnitudes to compute the PS zero points.
+
+The summary table is:
+|| filter || zero point || FWHM || DRM zero point ||
+|| g || 24.58 || ~.06 || 24.90 ||
+|| r || 24.80 || ~.06 || 25.15 ||
+|| i || 24.74 || ~.05 || 25.00 ||
+|| z || 24.26 || ~.05 || 24.63 ||
+|| y || 23.41 || ~.05 || 23.03 ||
+
+I'm just pulling these zero points and FWHM by eye off the following plots, looking for the good photometric clusters of points.
+
+[[Image(zptplotsg.png)]]
+[[Image(zptplotsr.png)]]
+[[Image(zptplotsi.png)]]
+[[Image(zptplotsz.png)]]
+[[Image(zptplotsy.png)]]
+
+The zero points are well-behaved enough that we can see the effects of atmosphere.  We get airmass extinction terms:
+
+|| filter || k_{PS} || k_{SDSS} ||
+|| g || .136 || .17 ||
+|| r || .182 || .10 ||
+|| i || .122 || .06 ||
+|| z || .079 || .06 ||
+|| y || .085 || --- ||
+
+Obviously there is a lot of uncertainty in the values I've given, and I haven't been very careful.  However, it is nice to see that they agree vaguely.
+
+The zero points have negligible temperature dependance:
+
+[[Image(zptplotstempg.png)]]
+[[Image(zptplotstempr.png)]]
+[[Image(zptplotstempi.png)]]
+[[Image(zptplotstempz.png)]]
+[[Image(zptplotstempy.png)]]
+
+The straight lines through the data are arbitrary lines I've added to make looking for deviations from flatness easier; temperature and zero point look awfully uncorrelated.