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NICMOS STScI Analysis Newsletter 30

| STScI Analysis Newsletter
| October 2003
Visit the NICMOS web site
"New in the Last 45 Days" for all new information about NICMOS.

CONTENTS (Optional):

-NICMOS Recovered from Safe Mode

-NICMOS Mini-Check Out
   -filter wheel test
   -focus monitoring
   -coma check

-NICMOS Coronagraphic Observations

-NICMOS Temperature Table

-NICMOS Polarimetry Calibration

-NICMOS Focus Monitor

-NICMOS post-SAA Darks

-Recent NICMOS Publications


NICMOS Recovered from Safe Mode

K. Noll

On Saturday August 2, 2003, the NICMOS Cooling System (NCS) 
was safed due to an input voltage reaching an out of limits
point. This resulted in a shutdown of all the cooler
systems. The NICMOS was safed (2003.214:21:56:43 UT) using
real time commanding in order to reduce the heat load within
NICMOS. The HST was in the South Atlantic Anomaly (SAA) at
the time of the safing. Subsequent investigation indicated
that a high energy particle caused an upset in the digital
register used to command the input voltage, causing it to
jump by 256 units. This then put the voltage out of range,
and caused the safing. There were no indications in the
engineering telemetry of any mechanical problem or permanent
electronic failure.

On August 7, 2003, the NCS circulator and compressor were
successfully restarted. Operation was nominal and the
circulator inverter input voltage, which caused the safing,
was at 6.06 V within normal range of the nominal value of
6.2 V. Active temperature control was achieved two days
later when the temperature set point of 77.1 K was reached 
(weighted average of the neon inlet and outlet temperatures).
The NICMOS was recovered from safe mode on August 14, 2003.
Science observations resumed on August 21, 2003.


NICMOS Mini-Check Out

K. Noll, S. Arribas, E. Bergeron, S. Malhotra, B. Mobasher,
E. Roye, A. Schultz, M. Sosey, T. Wiklind, C. Xu, and
G. Schneider.

Following recovery from Safe Mode, each of the NICMOS filter
wheels were exercised and flat field observations (lamp-off
and lamp-on) were obtained (program ID: 10062). Voltages and
currents were nominal during movement of the filter wheels.
Inspection of the flat field and dark observations obtained
in support of the filter wheel test confirmed motion of the
filter wheels to the commanded filter positions and back to
blank. No changes in debris on detectors (grot) were noted.
Flat field filter count rates were as expected.  No change.

Test program 10063, "NICMOS Focus and PAM Grid Tilt Tests"
executed on August 19, 2003.  The purpose of this program
was to measure the focus and coma to determine if they had
changed, and if necessary, to update them. The standard
focus target field, star cluster NGC3603, was observed with
NIC1 and NIC2.  A 17-point focus sweep was executed in each
camera, a  8mm movement of the PAM about its mechanical
zero point.  The focus was determined to be nominal in both
cameras.  No change.  Since the focus for NIC3 tracks the
focus in NIC1 and NIC2,  no change is expected and the
subsequent NIC3 observations withdrawn.

The observed coma was negligible, indicating that the PAM
tilt position had not changed.  Contingency visits were not
needed and withdrawn.


NICMOS Coronagraphic Observations 

G. Schneider and A. Schultz

NICMOS Cycle 12 Camera 2 coronagraphic science observations
started on August 26, 2003 with the observations of the
faint white dwarf GJ 3182 (mv=15.32). Due to the faintness
of the target, the flight software (FSW) acquired a bad
pixel even though the counts in the image of the target were
sufficient to acquire the target.  A brighter target would
not have had this problem. Bad pixels were identified and
the NICMOS Target Acquisition Pixel Gain Table onboard HST
was updated on September 12, 2003.  This pixel table, used
for all Mode-2 coronagraphic acquisitions, is specified for
targets of magnitude J ~4 to J ~18.  Subsequent Mode-2
acquisitions of faint targets have been successful.


NICMOS Temperature Table

A. Schultz

As an aid to NICMOS users, values of nine NICMOS Cooling
System (NCS) mnemonics and five NICMOS temperature sensors
are extracted from the engineering telemetry and bundled
together into a FITS table called the NICMOS Temperature
Table. The information in the table may be used in
calibration or temperature monitoring.  A table will be
created for each NICMOS observation and will have an
extension of epc (ipppssoot_epc.fits).  Currently, tables
are created and stored in OPUS until ingestion into the HST
Archive.  NICMOS observers may request tables from OPUS
in support of their observations.  Information about the table
can be found in NICMOS Instrument Science Report (ISR)
titled: "NICMOS Temperature Table," NICMOS-ISR-2003-008


NICMOS Polarimetry Calibration

D. Hines 

Cycle 11 polarimetry calibrations have been completed for
the NIC1 and NIC2 polarizers (program ID: 9644). The
polarization t(k)-coefficients, as explained in the NICMOS
explained in the NICMOS Data Handbook and in Hines, Schmidt
& Schneider (2000, PASP, 112, 983), have changed slightly
since Cycles 7 & 7N.  All other fundamental polarizer
coefficients remain unchanged.  Quantities derived from the
t-coefficients, such as the A, B and C terms in the
polarization reduction equation, should be regenerated using
the new t-values.  This exercise has been performed in the
new NICMOS manuals and is available from the NICMOS web site.

The new polarimetry calibrations should be used for all
NICMOS polarimetry data obtained after the NCS installation
(March 2002).  Using these revised coefficients, NICMOS is
capable of producing imaging polarimetry results with
accuracies of 1-2% (in percentage polarization), comparable
with its pre-NCS capabilities.

The new coefficients will be incorporated by D. Hines and
B. Stobie of the NICMOS IDT into the IDL polarimetry package
called "Polarize." This updated (but unsupported) package
will be available from the NICMOS public software site and
will be delivered to STScI.


NICMOS Focus Monitor

E. Roye and T. Wiklind

The results of the September 2003 NIC1 and NIC2 focus sweep
data indicate the focus is nominal, within 0.1 mm of the
current setting.  There was no NIC3 focus sweep this month.
The NIC3 focus sweep is scheduled for mid-October.
The latest focus plots have been posted on the NICMOS web


NICMOS post-SAA Darks

E. Bergeron and M. Dickinson

Latent or "persistent" images of cosmic rays hits following
HST transits of the South Atlantic Anomaly (SAA) can
significantly increase the noise in subsequent NICMOS science
images. A map of the persistent signal can be made from the
pair of post-SAA DARK exposures which are obtained
immediately following exit of the SAA.  This map can then
be used to subtract the latent "persistent" signal from
impacted images obtained in that orbit, thereby recovering
much of the original S/N.  Information describing the
problem and an algorithm to remove the persistent signal can
be found in NICMOS Instrument Science Report (ISR) titled:
"Removal of Cosmic Ray Persistence From Science Data using
the Post-SAA Darks,"  The algorithm has been coded in an
IDL routine called "" which is available upon
request from the STScI NICMOS web page. The
IDL routine is being converted into a stand-alone STSDAS
task for release at a future date.

| Recent NICMOS Publications
There are currently 53 NICMOS refereed publications for
2003.  Many NICMOS observations were retrieved from the HST
Archive in support of ground-based and HST observing programs.
Some publications reported new NICMOS observations as follow
up observations to existing programs.

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