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STIS Cycle-21 Calibration Phase-1

Last Revised: September 19, 2013
Proposal ID: 13551
Title: STIS NUV-MAMA Flats
PI: Hugues Sana
Co-I(s): Stephen Holland, Charles R. Proffitt

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# Orbit estimates are TOTAL for all of Cycle-21

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 binned pixel. The flats are obtained with the DEUTERIUM-lamp
and the MR grism G230M. The actual choice of central wavelength and
slit combination depends on the observed count level within each
exposure.


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 ~225297 cps. The first visit will need an
exposure time of 4630 sec as in program 11862. However, from the
second or third visit we might move to G230M/2419 (which will deliver
a factor 1.17 more counts, i.e ~263597cps) and exposure time of
3588sec, in order to possibly save ~2.9 hr of lamp lifetime.

Note that both the combination G230M/2338/52x0.5 and G230M/2419/52x0.5
are not coded in the "MAMA Flat Field Parameters Table" and therefore
require special handling during the visits. Namely, in order to avoid
that the a "safety procedure" is triggered and the deuterium lamp is
turned off, the special engineering parameters (quesiparms) TARGTYPE
and EXPADJ have to be specified as follow:

TARGTYPE = D2
EXPADJ = 438 whenever the parameter SLIT-STEP is NOT specified, and
EXPADJ = 442 whenever the parameter SLIT-STEP is specified.

These two values (438 and 442) have also to be added to the
EXPOSURE-TIME in order to guarantee that the exposure duration and the
flux level are the desired one.


Accuracy: 1.0%
Comments on Accuracy: Accuracy is per low-res pixel (2x2 high-res
pixels)
Products: combine this and past cycle frames to produce a new
reference p-flat and 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 (De lamp)
RA......................................: N/A
Dec.....................................: N/A
Flux (and units)........................: <=280000 count/s
Visibility window (if known or relevant): N/A

Comment on choice of target: Standard lamp for flat-field exposures.

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......................: 2419
Exposure Time...........................: 11x4030 S = 7399 M
BOP Predicted Local Count Rate for MAMA.: 0.2 count/s/low-res pixel
BOP Predicted Global Count Rate for MAMA: ~220000 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 12777. Count rate will
change as soon as the instrument setup will be modified.

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# Special needs of this proposal?

Scheduling:
About 1 visit per month, to allow inspection of the frames and timely
change of setup as necessary and to avoid waste of orbits in case of
lamp failure (as happened in the past).

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

PDB update? No
On-board table update? No

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

As the lamp illumination declines, we are obligated to change the
central wavelength and/or slit width in order to compensate, and so to
preserve the limited lamp lifetime. In case special commanding is not
available for the required setting, on-board table update will be
required.

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# Link to Cycle 21 Science

Fraction of science programs supported by this calibration:
40% 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): existing IDL code

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.