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Hubble Space Telescope
Phase I: 12081

COS Cycle-17 Calibration Phase-1 Template

Last Revised:			Date
Proposal ID:			(e.g. 9026)
Title: COS Flux Calibration Below 1150 Angstroms
PI:	Massa
Co-I(s): Osterman, Aloisi, Proffitt

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# Orbit estimates are TOTAL for all of cycle-17; assume 72 weeks) 

Total Prime Orbits:             5
External Parallel Orbits:       0
Internals or no-impact orbits:  0
Comments on orbit estimate:     one 5 orbit visit

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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:   
Measure the COS FUV (900 - 1150Ang) G140L sensitivity, determine if it 
has EUV (300-700) sensitivity, and explore the FUV G130M response.
Description:
We currently have a fairly accurate (10%) estimate of the G140L FUVB 
FUV sensitivity.  This is based on low S/N data of a faint standard star 
and a set of relatively high S/N spectra of a bright wd which cannot be 
accurately modelled.  The former have an accuracy worse than 20%, and the 
latter had to rely on FUSE absolute fluxes, which are only good to about 
10%.  Since this setting is now available to GOs, we should obtain an 
accurate (2-3%) charaterization of the FUV G140L sensitivity.  To do this, 
we intend to observe the hot wd GD50.  This star has high S/N IUE, FUSE and 
EUVE observations.  Further, it has been observed from the ground and its 
atmospheric parameters are reasonably well determined.  Both Pierre Chayer 
and Ralph Bolhin have agreed to produce the models needed to use it as a 
high quality FUV flux calibration source.  In addition, the existance a 
good GD50 EUVE spectrum means that the same observations can be used to 
characterize the EUV sensitivity to 10% accuracy, if estimates of the 
COS EUV sensitivity are correct.   

In addition to using GD50 to charaterize the FUV and EUV response for the 
G140L, it can also be used to perform an initial test of the FUV G130M 
response.  Because the response of the G140L drops by a factor of 70  
between 1150 and 1050 Ang, the targets it can observe will be limited.  
This is because many objects which are bright enough to obtain high S/N 
fluxes at 1050 Ang within a few orbits will exceed the local count rate 
limit at 1150 Ang.  On the other hand, the G130M can be moved to a new set 
of positions which only include wavelengths below 1050 Ang, circumventing 
the constraint imposed by the rapid decline in the response.  Because 
no observations have been made at these settings, we are not certain 
how sensitive the instrument will be.  GD50 will certainly be safe to 
observe at these new settings and although it may not provide enough 
counts to accurately calibrate them, a short observation at one setting 
will provide the information needed to develop an optimal calibration plan 
for the G130M short wavelength modes.  

NOTES: FUVA must be off for both the F140L and G130M observations 
     The new G130M setting will require new commanding.

Accuracy:              3% for G140L 900-1150A, 10% for 300-700A
                      9% for the G130M
Comments on Accuracy:  Accuracies are Poisson for 20 pixel bins
Products:              New G140L flux calibration file, an ISR on the 
                      potential of the G130M between 900 and 1150A.  

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# Link to Cycle 17 Science
# Use the GO + GTO Phase 1 exposure listing and derived statistics
# posted on WWW.

Fraction of science programs supported by this calibration:  
NA -- The spectrocsopic mode to be calibrated will only begin to be offered 
in Cycle 18, and there are no observations for the modes we propose to explore.

List categories of science which can't be executed until after this proposal:
Any EUV observation.
An optimal calibration program for the G130M response shortward of 1150 Ang.

why:  
The proposed observations will be the first to explore the COS EUV 
capabilities and the G130M response below 1150 Ang.  

List categories of science which are best performed contemporaneous with 
this proposal:
Programs which require accurate SED determinations below 1150 Ang. 

why:
The proposed observations will be the first to obtain high S/N data for a 
star that can be confidently modeled for use as a spectrophotometric standard 
in the FUV (below 1150 Ang).  

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# THE REST OF THIS FORM IS FOR INTERNAL USE
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Observation summary: 

Acquire and observe with the G140L FUVB for the first 3 orbits to obtain 
high S/N observations of the FUV and determine whether an EUV spectrum is 
detected.  Then switch to the new blue settings of the G130M: first the one 
that spans 1020 to 1171 Ang (1 orbit) and then the one that spans 905 to 
1055 Ang (1 orbit).  The selected G130M positions will explore the spectral 
regions expected to have the highest and lowest sensitivities.

# Target information (copy for each target)

Target Name.............................: GD50
RA......................................: 03 48 50.19 
Dec.....................................: -00 58 32.0
Flux (and units)........................: 
Visibility window (if known or relevant):
Comment on choice of target:
Brightest EUV source faint enough to observe with COS G140L/FUVB in the FUV.  

# 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..........................: GD50
Type of Acquisition.....................: ACQ/SEARCH+ACQ/PEAKXD+ACQ/PEAKD
Detector for observation................: FUVB
Operating mode .........................: TIMETAG
Spectral Element........................: G140L
Aperture................................: PSA
Central Wavelength......................: 1230
Exposure Time...........................: 30min+45min+45min
Number of Iterations ...................: 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.........: 
Comments: FUVA must be off



Target or lamp..........................: GD50
Type of Acquisition.....................: 
Detector for observation................: FUVB
Operating mode .........................: TIMETAG
Spectral Element........................: G130M
Aperture................................: PSA
Central Wavelength......................: 1100
Exposure Time...........................: 45min
Number of Iterations ...................: 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.........: Requires new grating setting
Comments: FUVA must be off.



Target or lamp..........................: GD50
Type of Acquisition.....................: 
Detector for observation................: FUVB
Operating mode .........................: TIMETAG
Spectral Element........................: G130M
Aperture................................: PSA
Central Wavelength......................: 980
Exposure Time...........................: 45min
Number of Iterations ...................: 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.........: Requires new grating setting
Comments: FUVA must be off.