| CAID: MIPS-148 | Title: SED Throughput Dependence on CSMM Position | |
| System: MIPS | Principal: psmith | Deputy: |
| Objective: | Determine the relative throughtput at the five possible scan mirror positions in SED mode (0 arcmin, +1, +2, +3) and see if there is a gradient. If a gradient is detected, we will want to choose the default source position to be in the region of higher transmission, and we will then need to scale our sky measurements before doing sky subtractions. |
| Description: | For this test, we need to point the telescope at a region of sky that is relatively bright and uniform at 70um. Using stim flashes for calibration, we observe the sky at the nominal CSMM relpos position. We then offset to +1 arcmin using relpos, but also issue a PCS command to compensate for that move and put the same patch of sky onto the SED slit. Again measure the brightness using stim flashes to track changes in the instrumental response. Repeat for positions +2 and +3 arcmin. Calculate the brightness at each of these four CSMM positions and see if there is a CSMM angle-dependent throughput gradient. The target sky position can be any relatively uniform 70um background that is bright. This IOC activity is not greatly affected by the choice of sky position for the slit as long as the telescope can be offset accurately (within a few arcsec) to compensate for the required changes in the CSMM position. A position chosen at low galactic lattitude will enable short integration times. |
| Day: 61.6062500000044 | Suggested Order: O500 | ||
| Must be preceded by these activities (list by CAID): MIPS-139 | |||
| Place in Schedule: This task should take place after it has been determined that telescope offsets are accurate to within a few arcsec. The task needs to be executed before the SED Slit Illumination Correction task (MIPS-299). | |||
| Priority: Desired | |||
Conditions | |||
| Maximum telescope temperature: | 12 K | ||
| Minimum telescope temperature: | 5.5 K | ||
| Should activity be repeated if focus changes? | No Repeat if focus changes by 0 mm | ||
| Maximum absolute pointing uncertainty: | 10 arcsec (1 sigma radial) | ||
| Maximum precision offset uncertainty: | 1 arcsec (1 sigma radial) | ||
| Observatory configuration: | Standard | ||
| Go/No Go criteria: | CSMM, CE, and detectors must be operational, instrument and telescope temperatures must be stable | ||
Duration: 30 minutes
| | Real time downlink:
No | | |||
| Data Volume (uncompressed): 150 Mbits | |||
| List Blocks, AORs, SERs, IERs, or unique sequences required (uplink): special IERs: stim flashes throughout to track response changes, DCEs at CSMM position 0, +1, +2, and +3 with no chop to "sky" | |||
| List Analysis tools required (downlink): Subset of standard pipeline, to get out slope images for each DCE, then custom tools to interpolate between stim flashes and determine brightnesses for each DCE. | |||
| Estimate of data turn around: 72 hours | |||
| Description: Determine the brightness of the sky in SED mode for each of the four CSMM angles. Plot a histogram of these brightnesses and determine if there is a statistically significant difference in brightnesses from one position to the next. If no significant gradient is found, then there is probably no need to return to this activity later in IOC (MIPS-148Q) and this test will not dictate any modifications to the data-taking or reduction strategies for SED mode. If a gradient is found, then MIPS-148Q should be executed to test the stability of the throughput variations and then the best CSMM position for objects observed in SED mode should be chosen. In addition, scaling factors will need to be calculated sky positions of the CSMM to correct for the throughput variation. | |||
| Can proceed in parallel with other activity: No | |||
| Must outcome be confirmed before next activity: No | |||
| Method of Confirmation: If we are not making a proper correction for throughput differences with CSMM position, poor sky subtraction will result in SED mode. This should become evident when we reduce SED data on a wide variety of sources. | |||
| Success criteria: Data with S/N high enough to determine if throughput in the SED mode is dependent on CSMM position. | |||
| Contingency plan: If we cannot make an unambiguous determination of whether there are throughput variations with CSMM angle in SED mode, we will have to rely on experience gained from reducing real science data to assess whether we are subtracting the sky correctly. | |||
Comments | |||
| References: | |||
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Additional Comments:
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| This activity last updated: 10/21/2002 2:42:29 PM | |||