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Hubble Space Telescope
NICMOS STScI Analysis Newsletter 34

| STScI Analysis Newsletter
| April 2005
Visit the NICMOS web site
"New in the Last 45 Days" for all new information about NICMOS.

CONTENTS (Optional):

-HST Cycle 14 Phase II Submission Deadline

-Release of APT 14.2 for HST Cycle 14

-New SPARS MULTIACCUM Timing Sequences

-Two Gyro Mode Guiding Test

-Time-Limited Non-Linear Response of NICMOS at Low Count Rates

-October 2005 Calibration Workshop

-HST 700,000 Observation


HST Cycle 14 Phase II Submission Deadline

Cycle 14 Phase II Submission Deadline is May 13, 2005.
Cycle 14 observing starts in July 2005.  Documentation and
tools necessary to develop, submit, and monitor your HST
Phase II proposal can be found on the Cycle 14 Phase II web


Release of APT 14.2 for HST Cycle 14

APT Team

APT 14.2 was released on April 7, 2005 in support of
Cycle 14 Phase II proposal development. An APT "Roadmap", a
step-by-step guide to writing a Phase II proposal, is
available at
Observers who need to refine a Cycle 13 proposal should
contact their Program Coordinator (PC) to determine which
version of APT they should use. APT 14.2 is available for
download from the APT web page.


New SPARS MULTIACCUM Timing Sequences


Four MIF MULTIACCUM timing sequences (MIF512, MIF1024,
MIF2048, and MIF3072) have been replaced by four new SPARS
MULTIACCUM timing sequences.  The four new timing sequences
are SPARS4, SPARS16, SPARS32, and SPARS128.  Each timing
sequence has two rapid reads at the beginning and end with
evenly spaced read outs of 4s, 16s, 32s, and 128s,
respectively. The new SPARS sequences can be most useful
for fields with faint sources; i.e., galaxies, nebulae, and
faint star clusters.


Two Gyro Mode Guiding Test


The Two Gyro Mode test was executed on February 21-23,
2005. The rate information from two gyros and one Fine
Guidance Sensor (FGS) at 40 Hz was input into the attitude
control law of the Pointing Control System (PCS).  A series
of NICMOS exposures were obtained to measure any possible
guiding anomalies (dither test), to measure the PSF
variability, and the performance of the NICMOS coronagraphy.
The actual on-orbit Two Gyro Mode average jitter (60 sec RMS)
for the gyro pair was ~6.2 mas with a maximum jitter
of ~7.3 mas.  The the jitter during the Two Gyro Mode test
was comparable to the three gyro mode jitter. Dithering was
successful indicating no affects due to Two Gyro Mode and
no measurable differences were found when comparing the
PSF FWHM for point sources obtained under Two Gyro Mode or
three gyro mode guiding.

Rolling the telescope within the same visibility period for
coronagraphy will not be allowed under Two Gyro Mode.  A roll
roll of the telescope between adjacent orbits was performed
for the the coronagraphic test. The observed coronagraphic
performance was essentially unaffected at 1.1 micron while
there was a slight decline at 1.6 micron. At r=10 pixels,
the coronagraphic suppression factor is 3 compared to direct
imaging, while it is a factor of 4 in three gyro mode. The
coronagraphic gains with Two Gyro Mode operations were still
substantial compared to direct imaging (Schultz et al. 2005


Time-Limited Non-Linear Response of NICMOS at Low Count Rates


A study designed to use the NICMOS grisms to extend faint
calibration standards beyond 1 micron found a previously
unseen effect. When compared to STIS and ACS in portions of
the spectrum where these instruments overlap in coverage with
NICMOS, the ratios of standards of different brightnesses 
are found to differ systematically (Bohlin et al. (2005
ISR-2005-002). The effect is most pronounced at shorter
wavelengths and disappears at wavelengths longer than 1.6
micron. However, the quantitative correction formula for the
observed non-linearity of the grism spectra may not be
applicable to point source photometry. Comparison of
photometry of faint sources in the UDF with ground-based
observations of the same sources failed to find significant
differences that would indicate a general problem with
NICMOS photometry (Mobasher et al. 2005 ISR-2005-003).  

In a separate study by A. Riess (unpub), examination of
intermediate reads in both the NICMOS grism data used by
Bohlin et al. and in other photometric observations shows
an apparent deficit in count rate at shorter exposure times.
The functional form of the trend is approximately exponential
with a time constant of about 150 seconds. This is the same
function that describes the release of charge in persistent
images and suggests that charge traps may be responsible for
the phenomenon. Integrations that begin with charge traps
unfilled will have a deficit in counts until the filling and
emptying of charge traps comes to equilibrium. This provides
a natural explanation for the observed effect in the NICMOS
grism observations used by Bohlin et al.. 

Most observations obtained for science will not be strongly
affected by this effect either because the integration times
are significantly longer than the 150 second e-fold time or
because the source count rates are sufficiently high that the
fraction of charge lost to traps is negligible. Scientific
observations at shorter wavelengths made with relatively
short integrations that compare bright and faint sources
obtained in the same exposure will be most vulnerable.
Examination of background-subtracted intermediate reads
from the ima file should be done by anyone concerned that
their observations may be measurably affected.

The NICMOS group will establish a dedicated link on the STScI
NICMOS Instrument page that will give all the details of this
phenomenon and will provide updated advice for cycle 14
Phase 2 proposals.


October 2005 Calibration Workshop

STScI will host an HST Calibration workshop Oct 26-29, 2005.
The goal of the workshop is to foster the sharing of
information and techniques between observers, instrument
developers, and instrument support teams.

We invite NICMOS observers to suggest calibration or
observing topics to be discussed at the workshop.


HST 700,000 Observation


On April 10, 2005, around 6:00pm EDT, HST took its 700,000th
exposure since launch of HST in April 1990.  This total
includes internal calibration exposures as well as targeted
observations using all nine Science Instruments that have
been or are still onboard HST (HSP, WFPC-1, FOS, GHRS, FOC,

The 700,000th Hubble exposure used the NICMOS for a parallel
observation in the Orion Nebula while the ACS was exposing on
a specific region under proposal 10246, "The HST survey of
the Orion Nebula Cluster", whose PI is Massimo Robberto of
STScI and ESA. This is a Treasury Program to perform a
definitive study of the Orion Nebula Cluster, the Rosetta
stone of star formation, with unprecedented sensitivity,
spatial resolution, and simultaneous spectral coverage over
a field centered on the Trapezium stars.

In addition, 30,000 astrometric science datasets using the
Fine Guidance Sensors have been processed since 1990 from
the engineering telemetry. The 30,000th astrometry
observation executed on April 4, 2005, for GO proposal 10107
by Douglas Gies (Georgia State U. Research Foundation), "The
Masses of the O-type Binary 15 Monocerotis."

| Recent NICMOS Publications

There are 25 NICMOS refereed publications for 2005. Many
NICMOS observations were retrieved from the HST Archive in
support of ground-based and HST observing programs. Some
publications reported new NICMOS observations while others
reported follow up observations to existing programs. A few
publications of note are listed below:

Apai, D., et al. 2005, "HST/NICMOS Observations of a
Proto-brown Dwarf Candidate," A&A, 433, L33-L36

Colbert, J.W., et al. 2005, "Near-Infrared Properties of
Faint X-ray Sources from NICMOS Imaging in the Chandra Deep
Fields," ApJ, 621, 587-595

Colina, L., Arribas, S., Monreal-Ibero, A. 2005,"Kinematics
of Low-z Ultraluminous Infrared Galaxies and Implications
for Dynamical Mass Derivations in High-z Star-Forming
Galaxies," ApJ, 621, 725-737

Figer, D.F. 2005, "An Upper Limit to the Masses of Stars,"
Nature, 434, 192-194

Sahai, R., Sanchez Contreas, C., Morris, M. 2005, "A
Starfish Preplanetary Nebula: IRAS 19024+0044," ApJ, 620,

Ueta, T., Murakawa, K., Meixner, M. 2005, "Hubble Space
Telescope NICMOS Imaging Polarimetry of Proto-planetary
Nebulae: Probing the Dust Shell Structure via Polarized
Light," AJ, 129, 1625-1641

A complete list of NICMOS publications by year can be
generated from the STScI Library home web page by clicking
the link "HST Biblography" and entering the year and
selecting NICMOS:

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