Summary of Expected Count Rates for MIPS as a Function of Target Brightness =========================================================================== Surface Brightness Count Rates: =============================== Conversion from Surface brightness to DN/s: MJ/sr --> mJy/px mJy/px --> e-/s/px e-/s/px --> DN/s/px MJ/sr --> mJy/px: ------------------- 4.25e+10 ""/sr * 1.e-9 MJy/mJy = 42.5 (MJy/sr) / (mJy/"") 24um: 2.55"^2/px 70um: 9.84"^2/px 160um: 16.0"^2/px 1MJy/sr = (""/px) / (42.5 MJy/sr * ""/mJy) 24um: 1 MJy/sr = 0.153 mJy/px 70um: 1 MJy/sr = 2.28 mJy/px 160um: 1 MJy/sr = 6.02 mJy/px Checked 160um vs. # from radiometric model, June 2002: 43mJy/px = 7.2MJy/sr ==> 1MJy/sr = 5.97 mJy/px Check! mJy/px --> e-/s/px --> DN/s/px: -------------------------------- Use the band-integrated response from MIPS chapter of SOM, table 8.2 (note that old label, 'Peak Response', was wrong, and the values are in fact band integrated response...) and the nominal gain values of 5.1 at 24um, and 7.1 for Ge. 24um Response: 420 e/s/mJy/px Gain: 5.1 e-/DN 70um Response: 140 e/s/mJy/px Gain: 7.1 e-/DN 160um Response: 80 e/s/mJy/px Gain: 7.1 e-/DN 24um: 82.4 DN/s/mJy/px 70um: 19.7 DN/s/mJy/px 160um: 11.3 DN/s/mJy/px Checked 160um vs. #s from radiometric model, June 2002: 7.2 MJy/sr = 4426 e-/s @ 18 A/W responsivity = 3197 e-/s @ 13 A/W responsivity 1 mJy/px = 73.8 e-/s @ 13 A/W responsivity = 10.4 DN/s @ 13 A/W responsivity Check! Full Conversion Factor MJy/sr --> DN/s: --------------------------------------- Mult. by (MJy/sr) / (mJy/px) conversion factor from above: 24um: 1 MJy/sr = 12.6 DN/s (was 11.8 DN/s for some reason) 70um: 1 MJy/sr = 44,8 DN/s (was 45.5 DN/s for some reason) 160um: 1 MJy/sr = 68.0 DN/s (was 66.3 DN/s for some reason) Note - these should be good to within a few percent of the radiometric model results according to the check done at 160 um. Surface-Brightness Saturation Limits ------------------------------------ These can be converted to saturation limits for extended emission using the saturation level in DN for each of the arrays. At 70 and 160 that is dicey because the responsivity changes over time, and a source that would not saturate immediately after an anneal could saturate some time later. I'll just estimate the saturation limit right after an anneal and worry about responsivity drifts later. Surface-Brightness Saturation Limits 1 MJy/sr Saturation Saturates in Advertised band (DN/s) Limit (DN) 10 sec (MJy/sr) Limit (Jy) -------------------------------------------------------------------- 24 11.8 6.e4 508 440 70WF 45.5 6.5e4 143 46 70NF 11.7 6.5e4 556 125 160 66.3 6.0e4 90 14 Typical Sky Backgrounds: ======================== SSC defines 3 background levels, Low, Medium, Hi: Background: Low Medium High Wavel MJy/sr DN/s MJy/sr DN/s MJy/sr DN/s ------------------------------------------------------------ 24 16.1 190 23.9 280 65.6 770 70 5.15 240 8.95 410 32.3 1500 160 6.53 430 16.5 1100 84.3 5600 In my 70 um Stimflash Amplitude report I defined statistical backgrounds using the IRAS/ISSA data. There I defined Low, Medium and High as corresponding to 50%, 80%, and 90% of the sky begin dimmer. The corresponding brightnesses and Count Rates are: JAS Background: Low Medium High Wavel MJy/sr DN/s MJy/sr DN/s MJy/sr DN/s ------------------------------------------------------------ 70 2.2 100 4.7 220 7.6 350 160 6.5 430 33 2200 68 4500 I repeated the statistical analysis using the COBE/DIRBE data (the ISSA data has the Zodiacal Light removed, and so was an innappropriate data set to analyze). From that I found: Low Medium High Lambda MJy/sr DN/s MJy/sr DN/s MJy/sr DN/s ------------------------------------------------------------- 25.0 36.06 426 57.31 676 64.27 758 60.0 12.26 558 20.47 931 23.23 1060 140.0 10.49 695 27.28 1810 50.02 3320 Same for All DIRBE bands: 1.2 0.43 0.77 1.17 2.2 0.30 0.61 1.04 3.5 0.20 0.38 0.63 4.9 0.68 0.88 0.97 12.0 19.69 29.71 32.89 25.0 36.06 57.31 64.27 60.0 12.26 20.47 23.23 100.0 9.41 16.24 26.17 140.0 10.49 27.28 50.02 240.0 6.75 20.40 40.27