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COS Cycle-19 Calibration Phase-1 Template

Last Revised: 01 August 2011
Proposal ID: 12719
Title: COS NUV Spectroscopic Sensitivity Monitor
PI: R. A. Osten
Co-I(s): A. Bostroem, C. Proffitt

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# Orbit estimates are TOTAL for all of cycle-19; assume 52 weeks)

Total Prime Orbits: 8
External Parallel Orbits: 0
Internals or no-impact orbits: 0
Comments on orbit estimate: observations quarterly: 4x1 for G230L, 4x1 for M modes


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# This section should be written with a GO audience in mind -- use
# Calibration plans in WFPC-2 handbook as a guide.

Purpose: Monitor sensitivity of each NUV grating mode to detect any change
due to contamination or other causes. The bare-Aluminum gratings on COS are
known to degrade with a rate which has been fairly steady since the start of
on-orbit operations.


Description: Obtain exposures in all NUV gratings --- G230L, G185M,
G225M, and G285M -- quarterly. The first two gratings
have stable behavior, while the last two are experiencing
sensitivity declines. However, they not used in
cycle 19, and the quarterly cadence in Cycle 18 was
sufficient to track the changes.
The main goal is to
track time dependence of sensitivity as a function of
wavelength. Because of the low usage of these modes, and their
fairly stable rate of decay, we have cut back on the number of
central wavelengths covered in this program. The G230L
monitoring observations will only cover the 2950 and 2635 central wavelengths;
the reddest cenwave (3360) contains contributions from second order light
in two stripes (as opposed to one for the other G230L gratings), and the
monitoring target is fairly dim at these wavelengths, requiring long integration times.
Decreasing the exposure times in the 2950 and 2635 exposures slightly will not
affect the determination of sensitivity declines.
The G185M grating has only ever had the 1921 central wavelength monitored for
spectroscopic sensitivity declines. Because it is the most heavily used
NUV grating in Cycle 19, we will add in the bluest cenwave (1786) to
monitor its behavior.
The G225M grating shows stable behavior
in terms of the sensitivity decline versus wavelength above 2100 A (consisten
from cenwave to cenwave),
with a slight lessening of the rate of sensivity decline below 2100 A.
In order to monitor this, only the G225M/2186 cenwave will be covered.
will be monitored. The G285M grating does show some small wavelength dependence
to the sensitivity decline (although this is not implemented in the TDS
reference file), and so we keep 2 cenwaves of this grating (2617 and 3094).


With the cuts described above, we will need 4 one orbit visits to monitor the G230L,
and 4 one orbit visits to monitor the G185M, G225M, and G285M gratings, for a total
of 8 orbits in Cycle 19.

Accuracy: SNR of 30 per resel at the central wavelength
Comments on Accuracy:
Products: ISR, Time-Dependent Sensitivity reference files


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# Link to Cycle 19 Science
# Use the GO + GTO Phase 1 exposure listing and derived statistics
# posted on WWW.

Fraction of science programs supported by this calibration:
11% of COS total exposure time.


List categories of science which can't be executed until after this proposal:
why:

List categories of science which are best performed contemporaneous with
this proposal:
why:


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# THE REST OF THIS FORM IS FOR INTERNAL USE
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Observation summary: Take spectra of WD1057+719 in G230L quarterly in central
wavelengths 2635, 2950.
Take spectra of G191B2B in the M-modes every quarter, covering one cenwave
of G185M, one of G225M, and two of G285M.

# Target information (copy for each target)

Target Name.............................: WD1057+719
RA......................................:
Dec.....................................:
Flux (and units)........................:
Visibility window (if known or relevant):
Comment on choice of target:

Target Name.............................: G191B2B
RA......................................:
Dec.....................................:
Flux (and units)........................:
Visibility window (if known or relevant):
Comment on choice of target:

# Exposure list plan at the Phase I level. Be as complete as reasonable.
# If possible information should be complete enough to allow easy
# submission of a Phase 2 from this form. However, if you have to leave
# some of the fields blank below, or want to provide the information
# in another format, that is acceptable. (Make sure you do the BOP checking
# though, as this is a phase-1 issue.)

Table of exposures (copy for each exposure as appropriate/desired):

Target or lamp..........................: e.g. G191B2B, or HITM
Type of Acquisition.....................: e.g. ACQ-PEAK
Detector for observation................: e.g. CCD
Operating mode .........................: e.g. ACCUM or TIMETAG
Spectral Element........................: e.g. G430L
Aperture................................: e.g. 50x0.5
Central Wavelength......................: e.g. 4300
Exposure Time...........................: e.g. 300s, crsplit=2
Number of Iterations ...................: e.g. 1
BOP Predicted Local Count Rate for MAMA.:
BOP Predicted Global Count Rate for MAMA:
ETC PID IDs for Count Rates.............:
Special Requirements or options.........: (e.g. GAIN=4; LOW-SKY)
Comments: (e.g. if monitoring, specify frequency)


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# Special needs of this proposal?

Scheduling: as indicated above

Prerequisites: (e.g., specific SMOV proposal; command development?)

PDB update? (Specify table name if known e.g. SIAF).
On-board table update? (Specify table name if known e.g. CCDBadPixelTable)

# Special Requirements:
Real time? N
Special commanding? N
Quick Data turnaround? N
Special timing required? Y
Other? N
Describe (& justify) special requirements:
timing is described above

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# Analysis Plan

Expected FTE weeks for analysis: 3 weeks
Required turnaround on analysis (weeks): 1
Data volume (Mb needed for analysis): 0
Special software needed for analysis? (Describe): existing IDL programs

Description of analysis Plans: Use existing IDL code to make ratios of spectra with
those obtained at the beginning of the monitoring. After averaging in wavelength,
plots of these trends with time determine the time-dependent sensitivity. These values
are used to update TDS reference files.

To get the data and run scripts will take 3-4 hours per visit (L+M combined), so an upper limit of 16
hours for a quicklook analysis for the entire program. Making a new reference file will take
1-2 weeks for testing and documentation.