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STIS Cycle-19 Calibration Phase-1

Last Revised: 01/08/2011
Proposal ID: 12777
Title: MAMA NUV Flats
PI: Elena Mason
Co-I(s): Charles R. Proffitt, Michael A. Wolfe

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# Orbit estimates are TOTAL for all of Cycle-19

Total Prime Orbits: 0
External Parallel Orbits: 0
Internals or no-impact orbits: 11
Comments on orbit estimate: 11 single-orbit visits to build S/N

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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:

This program is aimed at obtaining NUV-MAMA flat-field observations
for the construction of pixel-to-pixel flats (p-flats) with a SNR of
~100 per pixel. The flats are obtained with the DEUTERIUM-lamp and the
MR grisms G230M. The actual choice of central wavelength and slit
combination depends on the observed count level within each exposure.

Note that STIS NUV-MAMA flats are taken every other cycles
(i.e. during odd number cycles) in order to not drain the DEUTERIUM
lamp lifetime.

Description: Past experience and observations have shown that ~11
visits are sufficient to build a p-flat with the required SNR~100/pix
(2x2 "binning", low-res mode). However the actual instrument setup
(central wavelength and slit width) and exposure time might change
during the cycle in order to guarantee the needed count-level of
~250000-280000 cps/frame. Past experience and observations have also
shown that NUV-MAMA p-flats are mode independent, i.e. they do not
depend on the wavelength. Therefore, a high-quality p-flat constructed
with the G230M suffice all NUV-MAMA spectroscopic and imaging
programs.

The G230M flats will be taken with the slit at 5 different offset
positions in order to illuminate also those detector region which are
normally shadowed by the slit bars. The first visit will be performed
with G230M centered at 2338A and the slit 52x0.5 (as in program 11862)
for which we estimate ~23953cps. The first visit will need an exposure
time of 4360. sec. However, from the second or third visit we might
move to G230M/2419 (which will deliver a factor 1.17 more counts,
implying a cps<=279926.) and exposure time of 3367sec, in order to
possibly save at least 2.5hr of lamp lifetime.


Accuracy: 1.0% (0.5% if combined with all previous P-flats)
Comments on Accuracy: Accuracy is per low-res pixel (2x2 high-res pixels)
Products: reference file (P-flat) and ISR as applicable

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# THE REST OF THIS FORM IS FOR INTERNAL USE
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# Target information (copy for each target)

Target Name.............................: NONE (D2 lamp)
RA......................................: N/A
Dec.....................................: N/A
Flux (and units)........................: 280000 counts/s
Visibility window (if known or relevant): N/A
Comment on choice of target: Standard lamp for flat-field exposures.

# Observing plan at the Phase I level. Be as complete as reasonable. As much as
# possible information should be complete enough to allow easy
# submission of a Phase 2 from this form. Can either describe in sentences
# or use the exposure templates below.


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

Target or lamp..........................: Deuterium
Type of Acquisition.....................: N/A
Detector observation....................: NUV-MAMA
Spectral Element........................: G230M
Aperture................................: 52x0.5
Central Wavelength......................: 2338 or 2419
Exposure Time...........................: 1-2*4360 + 10-9*3367s
BOP Predicted Local Count Rate for MAMA.: 0.26-0.27 count/s/low-res pixel
BOP Predicted Global Count Rate for MAMA: 280000 count/s
ETC PID IDs for Count Rates.............: [see comments]
Special Requirements....................: SLIT-STEP=-3360, -1680, 0, 1680, 3360

Comments: Count rate based on observations from program 9625. The
choice of central wavelengths is based upon high lamp
output, and avoidance of emission lines in the
spectra.

MAMA plate scale along slit is 0.029 arcsec/pixel,
fiducial bars are 0.5 and 0.86 arcsec, and the slit
wheel steps 35 units per pixel. So the SLIT-STEP
positions will cover the center of the largest
fiducial, and roughly +/- 30%, and +/- 60% of the
largest bar width from the center.

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# Special needs of this proposal?

Scheduling:
Visits should be spread across the period. In additions, it is
preferred if at least 2 weeks separate visit 1 from visit 2 thus to
allow for verification of the flat count level and the following
visits modification as necessary.

Prerequisites:

PDB update? No
On-board table update? Yes

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

As the lamp illumination declines, we might be obligated to change
central wavelength and/or slit width in order to compensate, and so to
preserve the limited lamp lifetime.

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# Link to Cycle 19 Science

Fraction of science programs supported by this calibration:
47% of STIS total exposure time.

List categories of science which can't be executed until after this
proposal: None.

List categories of science which are best performed contemporaneous with
this proposal:
None.

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# Analysis Plan

Expected FTE weeks for analysis: 4
Required turnaround on analysis (weeks): 16
Data volume (Mb needed for analysis): 100
Special software needed for analysis? (Describe):

Description of analysis Plans: (1-2 paragraphs)

Global count rates and engineering data will be examined to determine
the extent of lamp degradation, and whether it matches predictions
from current on-orbit experience. Flats will be combined, and a
solution for the slit illumination and spectral distribution of the
lamp will be derived and removed to create P-flats.