Changes between Version 10 and Version 11 of IPP_Progress_Report_20110425

Timestamp:

May 3, 2011, 11:36:45 AM (15 years ago)

Author:

eugene

Comment:

--

IPP_Progress_Report_20110425

@@ -5 +5 @@
 
 === Eugene Magnier ===
+
+I've spent the week working on two somewhat related issues.  First, I have been looking into the photometric quality of the 3pi reference database we have generated.  I have been using the stellar locus as a test of the photometry.  The results are somewhat mixed.   For some large areas, the stellar locus test suggests that we are getting the right answer to an acceptable level of ~2%.  This measurement is limited partly by the stellar locus itself and by astrophysics: I clearly see the effects of extinction in the Galactic Plane.  Some other regions have stellar locus offsets which are larger than our goal.  These tend to be blocks, which suggests these are the residual impact of weather.  There are also some regions for which the measured zero points to not appear to have converged on a valid result; this is not expected, and suggests that the relative photometry analysis needs to be re-run for those areas.  I am still examining this issue.  Meanwhile, we have released the next 3pi dvo database snapshot (demo month to 2011/04/01) and I have started the process of running the reference database analysis on that snapshot.
+
+The other issue I have been concerned with this week is the aperture correction / growth correction measured by psphot.  I have noted seeing-dependent photometry in the past (clearly measured in the MD fields), and I have attributed this to the growth correction or the size of the reference aperture.  I ran an experiment with 2 nights of MD data for which the seeing dependency was clear, using a set of different reference apertures.  To my surprise, the size of the aperture did not affect the zero point offsets between the two nights.  I have turned to simulated data (with the PS1-style power law psf) to understand the source of the seeing dependence.  So far, I have not been able to make a correction to the photometry which does not retain some seeing dependence (at the ~2% level).  It is possible that we will need to correct the photometry with an empirical seeing model derived from the MD field data.
 
 === Serge Chastel ===