Changes between Version 2 and Version 3 of StarGalaxySeparation

Timestamp:

Oct 21, 2010, 5:51:36 AM (16 years ago)

Author:

eugene

Comment:

--

StarGalaxySeparation

@@ -9 +9 @@
 We found that the moments did not improve the star/galaxy separation.  Instead, because of the variable PSF, including moment information tended to increase the noise in the measurement.
 
+This first figure shows an example of the GPC1 / SDSS comparison.  The green dots are the SDSS-identified stars; the blue dots are the SDSS-identified galaxies; the red dots are not identified in SDSS. The plot on the left shows the Kron magnitude - PSF magnitude vs PSF magnitude (all PS1 measurements).  The plot in the middle shows the SDSS model magnitude - SDSS PSF magnitude from the deep stack (this is essentially the SDSS star/galaxy separation analysis).  The plot on the right shows the (Kron magnitude - PSF magnitude - median offset) / sigma (PSF error, Kron magnitude error, 0.01 mags all added in quadrature). We generated plots like the above for 15 exposure, and they all exhibit more-or-less the same behavior.  
 
+The right hand plot is the PSF-significance: it represents the significance (in terms of a Gaussian sigma) of the PSF nature of the object.  The larger the value in this plot, the less likely the object is taken from a population of PSF-like objects.  We consider this to be a measurement of the a-priori star probability.  
 
-    *   pssg-hists-0.png  (82.9 KB) - added by eugene  2 minutes ago.
-    * pssg-hists-1.png (69.7 KB) - added by eugene 112 seconds ago.
-    * pssg-hists-sn-0.png (81.0 KB) - added by eugene 100 seconds ago.
-    * pssg-hists-sn-1.png (47.0 KB) - added by eugene 94 seconds ago.
-    * im-0.png (115.7 KB) - added by eugene 70 seconds ago.
-    * o5466g0311o.231829.cm.125673.kmag.png (44.0 KB) - added by eugene 11 seconds ago.
+[[Image(im-0.png)]]
+
+The second figure shows a series of histograms of the right hand plot above, summed over all exposures.  Each histogram is a different PSF magnitude range.  This sequence shows the reliability of the PSF-significance as a measurement of the a-posteriori galaxy probability as we proceed to fainter magnitudes.  In these histograms, the black line is all objects; the green line is the SDSS-identified stars; the blue line is the SDSS-identified galaxies; the red line is the objects not identified in SDSS.
+
+|| [[Image(pssg-hists-0.png)]] || [[Image(pssg-hists-1.png)]] ||
+
+The third figure shows an equivalent series of histograms, but this time in terms of the PSF signal-to-noise.
+
+[[Image(pssg-hists-sn-0.png)]] || [[Image(pssg-hists-sn-1.png)]]
+
+=== Cosmic Ray detection ===
+
+We also are able to examine sources not identified by SDSS, many of which are cosmic rays.  We find that the second moment minor axis (M_minor_) is the most useful indicator of the cosmic rays.  As an example, the figure below shows M_minor_ for one of the Stripe 82 exposures above.  
+
+[[Image(o5466g0311o.231829.cm.125673.kmag.png)]]
+