Principal: dmkelly
Deputy: eyoung
Data Monkey(s): I will probably recruit some help from the Sili monkeys.
Priority: Necessary
Downlink Priority: Normal
Analysis Time: 72h
Last Updated:
For each of the four bias settings: # collect 50 10s DCEs of read noise data sendcmd CEMIPSUR 'AORID_upper,AORID_lower,0,"NO_COADD",9,50,"MIPS"' # collect photometric data on a calibration star 24umCompactSourcePhotAOT (AORTarget=MIPS-920 calibration star, cycle=2, 3s DCEs)
Here is the full AOR: # Read noise and photometry for the nominal bias of 1.5V sendcmd mips_rn24um_10s50 24umCompactSourcePhotAOT (AORTarget=MIPS-920 calibration star, cycle=2, 3s DCEs) # Set 24um bias voltage to 1.25V by setting VD24SubVlt to 3.75V sendcmd CELDTPGIF '0,0x97,"MIPS"' # wait for the detector to settle wait 600 # Read noise and photometry for 1.25V bias sendcmd mips_rn24um_10s50 24umCompactSourcePhotAOT (AORTarget=MIPS-920 calibration star, cycle=2, 3s DCEs) # Set 24um bias voltage to 1.00V by setting VD24SubVlt to 4.00V sendcmd CELDTPGIF '0,0xA1,"MIPS"' # wait for the detector to settle wait 600 # Read noise and photometry for 1.0V bias sendcmd mips_rn24um_10s50 24umCompactSourcePhotAOT (AORTarget=MIPS-920 calibration star, cycle=2, 3s DCEs) # Set 24um bias voltage to 1.75V by setting VD24SubVlt to 3.25V sendcmd CELDTPGIF '0,0x83,"MIPS"' # wait for the detector to settle wait 600 # Read noise and photometry for 1.75V bias sendcmd mips_rn24um_10s50 24umCompactSourcePhotAOT (AORTarget=MIPS-920 calibration star, cycle=2, 3s DCEs) # Set 24um bias voltage to 1.5V by setting VD24SubVlt to 3.5V sendcmd CELDTPGIF '0,0x8D,"MIPS"' # wait for the detector to settle wait 600
Array Data Desired:
24um array data
Data Reformatting Option:
Special Instructions:
The 50 DCEs of read noise data should be packed into one FITS file. The photometry data should be packed into one FITS file. Data will be collected at four bias voltages, for a total of 8 FITS files.
1) Median standard star brightness, averaged over all observations in the photometry AOT, tabulated and plotted as a function of array bias 2) Dark level from the read noise data, tabulated and plotted as a function of bias 3) Standard star repeatability 4) Read noise, tabulated and plotted as a function of bias 5) A report listing the optimum bias voltage, along with an explanation of how the input criteria led to this selection
Step by step analysis: 1) Use mips_sloper to reduce the data. Use flags -b -d -l on darks. Set no flags for the standard star observations. 1) Perform photometry on the standard star AOT data, using IDP3 or something similar. 2) Calculate the mean and sigma of the standard star fluxes 3) Use get_rdnoise on the 24um data to calculate read noise and dark current 4) Plot standard star brightness, dark current, read noise, and source repeatability versus detector bias 5) Use a TBD method to combine the above results into a figure of merit for determining the optimum bias setting
mips_sloper get_rdnoise.pro photometry tool for determining standard star fluxes, probably IDP3
The preferred source for this task is HD 159330, the 24um calibrator that
will be used by Chad in campaign H, mips-920. This star is also observed
in campaign E, mips-120, stim calibration with celestial sources.
The 24um array saturates in 1s for a brightness of 5.6 Jy. This source
saturates in about 11s and so is perfect for 3s integrations. It
will work well for all four bias voltages.
Source F24 F70 F160 B24 B70 B160 Vis. window
(Jy) (MJy/sr)
HD 159330 0.515 0.06 0.01 18.6 5.5 5.8 April 16 -- Nov 23
In our instrument-level tests of the 24um array, we adopted an optimum
bias value of 1.5 V. In a ground-based test environment, the Si:As 24um
detectors are very well behaved. Their read noise is low (about 9 DN),
and the dark current is small (2-3 DN/s). The detectors provide good
stability. Their response grows with increasing bias, and there is no
breakdown of the detectors until the bias gets well above 1.5 V. An
analysis of the optimum bias is very likely to indicate that we would
be better off with a bias in excess of 1.5 V.
In space, the detectors will be subject to a harsh radiation environment.
For the most part, the detector behavior will still be excellent. But
over time, the radiation will cause damage, and that damage will lead
to a slow degradation in the performance of the array. The damage accrues
more quickly with increasing detector bias, and the spikiness and
nonlinearities are worse the higher the bias on the detector. As a
result, we expect to use a modest 24um bias during the early part of
the mission, and we are prepared to reduce the bias later in the mission
as radiation damage builds up.
Cosmic ray effects are difficult to account for in ground-level
testing. In this IOC task, we will be attempting to understand the
benefits and disadvantages of running the 24um detector at higher
or lower bias than the nominal value of 1.5 V. These results are
unlikely to change our mind about how to run the array during the
early part of the mission, but they will provide a reference for
deciding when and by how much to change the bias on the array later
in the mission.