DARK CURRENT AS FUNCTION OF EXPOSURE

I have examined several of the DC vs Exposure time sequences. All the analyses use the Average 16 image files unless otherwise noted.

CCD2 Low Temperature (-40 C)

dc_exp1_loT.gif (filename of plot; plot made with dc_exp.pro)

The CCD2 dark current as function of exposure ( list of images used in plot). Note the negative slope, this is opposite of what I would expect.

CCD2 Medium Temperature (-30 C)

These data were acquired with the least amount of oil contamination (see previous reports) and thus I have done the mostwork on this set.

dc_exp1_medT.gif (filename of plot; plot made with dc_exp.pro)

The CCD2 dark current as function of exposure ( list of images used in plot).

 Filename	   Mean		STD	EXP	TEMP
-----------------------------------------------------
20580049.FIT      64.9049      5.46509	100	-33.7	
20580089.FIT      64.6021      5.47302	500	-33.4
20580129.FIT      64.0439      5.49677	917	-33.0

Note that the DNS are decreasing with increased integration time (negative slope), hmmmm.... And also notice that the temp is also increasing slowly, which should tend to increase the DNs.

CCD2 High Temperature (-20C)

dc_exp1_hiT.gif (filename of plot; plot made with dc_exp.pro)

The CCD2 dark current as function of exposure ( list of images used in plot). Note the positive slope.

CCD2 Room Temperature (? C)

dc_exp1_roomT.gif (filename of plot; plot made with dc_exp.pro)

The CCD2 dark current as function of exposure ( list of images used in plot). Note the positive slope.

COMMENTS

I find it curious that for the low and med temperature runs that dark decreases as exposure increases. However for high and room temperature the dark increases with longer exposure, as I would expect. Why do I observe this behaviour?