Changes between Version 43 and Version 44 of Durham_MDS_Testing

Timestamp:

Aug 19, 2009, 12:19:19 AM (17 years ago)

Author:

shaun.cole@…

Comment:

--

Durham_MDS_Testing

@@ -72 +72 @@
 Here is a comparison of the PSFmags from the cmf files of four adjacent (arbitrarily chosen) MD07 stacks with SDSS model mags (r,g,i and z, as labelled). Blue indicates an object flagged as a star by SDSS. I haven't rejected any images flagged as defective in any way, so this probably explains the blue points offset by 2 mags. UPDATE: looks like these offset points are stars with masked centres - note that there are brighter stars which are not masked. Is this the 'removing intermediate brightness stars as cosmic rays' problem again? It appears particularly bad on r cells 40 and 52.
 
-Clearly the zero-point varies from cell to cell (do we expected this? after all, no calibration has been done as far as I can tell). The r-band stellar locus also appears tighter in cell 41 than in the other r-band cells. As the are no extended source magnitudes in the cmf files, all the galaxies (black open circles) are offset.
+Clearly the zero-point varies from cell to cell (do we expected this? after all, no calibration has been done as far as I can tell - '''YES''' ''the zero point depends on the number of warps which went into the stack''). The r-band stellar locus also appears tighter in cell 41 than in the other r-band cells. As the are no extended source magnitudes in the cmf files, all the galaxies (black open circles) are offset.
 
 [[Image(MD07_rband_sdss_v2.jpg, 600px)]] [[Image(MD07_gband_sdss.jpg, 600px)]]
@@ -78 +78 @@
 [[Image(MD07_iband_sdss.jpg, 600px)]] [[Image(MD07_zband_sdss.jpg, 600px)]]
 
-Update: I have now  done the SDSS comparisons for all the MD07 stacked skycells. Here are the histograms of the zero-point distributions. Outliers have been clipped before determining the mean and rms.
+Update: I have now  done the SDSS comparisons for all the MD08 stacked skycells. Here are the histograms of the instrumental zero-point distributions, corrected for the number of warps which went into each skycell. In z, one outlier has been clipped before determining the mean and rms.
 
-[[Image(md07_r_zp.jpg,400px)]] [[Image(md07_g_zp.jpg,400px)]]
+[[Image(md08_r_zp.jpg,400px)]] [[Image(md08_g_zp.jpg,400px)]]
 
-[[Image(md07_i_zp.jpg,400px)]] [[Image(md07_z_zp.jpg,400px)]] 
+[[Image(md08_i_zp.jpg,400px)]] [[Image(md08_z_zp.jpg,400px)]] 
 
-I have now done MD08. The (clipped) means of all skycells are:
+g 33.63 +/- 0.05
 
-g 33.61 +/- 0.06
+r 34.16 +/- 0.04
 
-r 34.13 +/- 0.07
+i 33.93 +/- 0.06
 
-i 33.90 +/- 0.05
+z 33.59 +/- 0.06 (cell 074 with a zp of 35.2 has been excluded)
 
-z 33.58 +/- 0.04
-
-The file attachment:md07_stack_zeropoints lists the zero points for each skycell in g,r,i and z. attachment:md08_stack_zeropoints is the version for MD08.
+The file attachment:md08_stack_zeropoints lists the zero points for each skycell in g,r,i and z, both before and after correction for the number of warps.
 
 == zeropoints in stacked frames == #zeropoints-stacked
 
-I have measured the zeropoints from the MD07/08 stacks, from comparing IPP cmf uncalibrated PSF mags with SDSS
+Using the data above, I have measured the zeropoints per second from the MD07/08 stacks, presuming 19, 25, 20 & 24 warps went into the g,r,i & z stacks respectively (these numbers came from the dbinfo files for each stack).
 
 ||filter||MD07||MD08||
-||g||24.46||24.42||
-||r||24.68||24.71||
-||i||24.70||24.70||
-||z||24.18||24.23||
+||g||     ||24.48||
+||r||     ||24.71||
+||i||     ||24.73||
+||z||     ||24.19||
 
-These are all slightly brighter (0.05-0.1) than [wiki:GPC_Zero_Points_July09 Eddie Schlafly's values]. There will be correction (of the right sign) for light missing outside the IPP PSF though.
+Apart from the i-band, these are all slightly brighter (0.05-0.1) than [wiki:GPC_Zero_Points_July09 Eddie Schlafly's values]. There will be correction (of the right sign) for light missing outside the IPP PSF though (''Eugene says this should affect both sets of measurements'').
 
 --Nigel