Changes between Version 6 and Version 7 of Background_Dark_Model

Timestamp:

Mar 7, 2012, 3:27:34 PM (14 years ago)

Author:

watersc1

Comment:

--

Background_Dark_Model

@@ -46 +46 @@
 
 I've requested that a sequence of darks be taken to more finely cover the range of exposure times, and will use this data to develop a more complete dark model that will hopefully not introduce any residual gradients.
+
+== March 7, 2012 ==
+
+I've reduced a series of dark exposures taken since February 01 2011, as this was the time the current dark model was constructed.  I've fit the slope in cell xy10 of OTA67 as a proxy measure of the dark quality, as this cell shows an introduced gradient that appears to contribute to false positives.  Shown below is a profile cut across this cell and the others in that OTA and cell row (cells xy10-xy16).  The two profiles shown are from subsequent nights at the beginning of the date range considered, and show different residual patterns.  Broadly, we can group nights with increasing gradients with x-pixel on a cell as Mode A, and those with decreasing gradients as Mode B.
+
+[[Image(profiles4.png,400px)]]
+
+The slopes of the first cell were checked for four data samples:
+ 1. A random sampling of dark frames from the night long dark series (night of UTC 2012-03-07).
+ 1. A selection of 30s dark frames from each night, chosen from the second dark sequences of the morning and evening.
+ 1. A random sampling of all parameter space.
+ 1. All darks taken on MJD 5591 and 5592, to investigate inter-night changes.
+
+[[Image(ccdtemp4.png,400px)]]
+
+[[Image(exptime4.png,400px)]]
+
+[[Image(pontime4.png,400px)]]
+
+[[Image(dateobs4.png,400px)]]
+
+It appears from these data that prior to about 2011-05-01, the camera (or at least OTA67) flipped between the two dark modes without any obvious pattern.  The data from MJD 5591 and 5592 show that even adjacent nights can have different patterns.  However, after 2011-05-01, the camera settled into what appears to be a single mode, which has persisted since.  
+
+Based on this observation, I'm currently constructing a new dark master from data taken after 2011-05-01, which should fit all exposures after this point.  However, there is no clear idea why this mode has become dominant.  A voltage change was done around this time to solve the STS Astrometry bug, but OTA67 was not one of those with a change.
+
+[[Image