Daily Report #4328

Notice: For the foreseeable future, the daily reports may contain apparent
discrepancies between some proposal descriptions and the listed instrument
usage. This is due to the conversion of previously approved ACS WFC or HRC
observations into WFPC2, or NICMOS observations subsequent to the loss of
ACS CCD science capability in late January.

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT # 4328

PERIOD COVERED: UT March 27, 2007 (DOY 086)

OBSERVATIONS SCHEDULED

FGS 10612

Binary Stars in Cyg OB2: Relics of Massive Star Formation in a
Super-Star Cluster

We propose to make a high angular resolution SNAP survey of the massive
stars in the nearby, super-star cluster Cyg OB2. We will use FGS1r TRANS
mode observations to search for astrometric companions in the separation
range of 0.01 to 1.00 arcsec and in the magnitude difference range smaller
than 4 magnitudes. The observations will test the idea that the formation of
very massive stars involves mergers and the presence of nearby companions.
Discovery of companions to massive stars in this relatively nearby complex
will provide guidance in the interpretation of apparently supermassive stars
in distant locations. The search for companions will also be important for
verification of fundamental parameters derived from spectroscopy,
adjustments to main sequence fitting and distance estimations, determining
third light contributions of eclipsing binaries, identifying wide colliding
wind binaries, studying the relationship between orbital and spin angular
momentum, and discovering binaries amenable to future mass determinations.
The massive star environment in Cyg OB2 may be similar to the kinds found in
the earliest epoch of star formation, so that a study of the role of
binaries in Cyg OB2 will help us understand the formation processes of the
first stars in the Universe.

FGS 10989

Astrometric Masses of Extrasolar Planets and Brown Dwarfs

We propose observations with HST/FGS to estimate the astrometric elements
{perturbation orbit semi-major axis and inclination} of extra-solar planets
orbiting six stars. These companions were originally detected by radial
velocity techniques. We have demonstrated that FGS astrometry of even a
short segment of reflex motion, when combined with extensive radial velocity
information, can yield useful inclination information {McArthur et al.
2004}, allowing us to determine companion masses. Extrasolar planet masses
assist in two ongoing research frontiers. First, they provide useful
boundary conditions for models of planetary formation and evolution of
planetary systems. Second, knowing that a star in fact has a plantary mass
companion, increases the value of that system to future extrasolar planet
observation missions such as SIM PlanetQuest, TPF, and GAIA.

NIC2 10603

Multiwavelength Imaging of Edge-on Protoplanetary Disks: Quantifying the
Growth of Circumstellar Dust

Young, edge-on circumstellar disks are uniquely valuable laboratories for
the study of planet formation. In these objects, the central star is
occulted from direct view, significant PSF artifacts are absent, and the
disk is clearly seen as a central dust lane flanked by faint disk reflected
light. The detailed morphology of these nebulae and its variation with
wavelength provide crucial information on the disk internal structure and
the properties of its constituent dust grains. A key observable is the slope
defining the wavelength dependence of the dust scattering opacity, which
becomes shallower when grain growth has taken place; multiwavelength
resolved disk images are the key dataset enabling such measurements. Recent
analyses of three different edge-on disks have revealed a diversity in their
dust properties that is indicative of different degrees of dust grain
evolution having taken place in each system. This characterization of disk
grain growth, when applied comparatively to a larger sample of these
objects, would enable the construction of an evolutionary sequence of young
disks at successive stages on the road to planet formation. In pursuit of
this goal, we have identified a sample of 15 edge-on disks previously
discovered by HST or groundbased telescopes, but for which high fidelity,
high spatial resolution images do not yet exist in both the optical and
near-infrared. We propose broad- band multicolor imaging with NICMOS of all
these targets, and ACS imaging of nine of these targets In combination with
existing data, the proposed images will form a complete database of high
resolution optical/near-IR images for these 15 disk systems. Scattered light
modeling will be used to derive the disk structure and dust properties,
yielding results that will be of fundamental importance for our
understanding of grain properties during protoplanetary disk evolution.

NIC2 10849

Imaging Scattered Light from Debris Disks Discovered by the Spitzer Space
Telescope around 21 Sun-like Stars

We propose to use the high-contrast capability of the NICMOS coronagraph to
image a sample of newly discovered circumstellar disks associated with
Sun-like stars. These systems were identified by their strong thermal
infrared {IR} emission with the Spitzer Space Telescope as part of the
Spitzer Legacy Science program titled "The Formation and Evolution of
Planetary Systems" {FEPS, P.I.: M.Meyer}. Modeling of the thermal excess
emission from the spectral energy distributions alone cannot distinguish
between narrowly confined high-opacity disks and broadly distributed,
low-opacity disks. By resolving light scattered by the circumstellar
material, our proposed NICMOS observations can break this degeneracy, thus
revealing the conditions under which planet formation processes are occuring
or have occured. For three of our IR-excess stars that have known
radial-velocity planets, resolved imaging of the circumstellar debris disks
may further offer an unprecedented view of planet-disk interactions in an
extrasolar planetary system. Even non-detections of the light scattered by
the circumstellar material will place strong constraints on the disk
geometries, ruling out disk models with high optical depth. Unlike previous
disk imaging programs, our program contains a well-defined sample of ~1
solar mass stars covering a range of ages from 3 Myr to 3 Gyr, thus allowing
us to study the evolution of disks from primordial to debris for the first
time. The results from our program will greatly improve our understanding of
the architecture of debris disks around Sun-like stars, and will create a
morphological context for the existence of our own solar system. This
proposal is for a continuation of an approved Cycle 14 program {GO/10527,
P.I.: D. Hines}.

WFPC2 11030

WFPC2 WF4 Temperature Reduction #3

In the fall of 2005, a serious anomaly was found in images from the WF4 CCD
in WFPC2. The WF4 CCD bias level appeared to have become unstable, resulting
in sporadic images with either low or zero bias level. The severity and
frequency of the problem was rapidly increasing, making it possible that WF4
would soon become unusable if no work-around were found. Examination of bias
levels during periods with frequent WFPC2 images showed low and zero bias
episodes every 4 to 6 hours. This periodicity is driven by cycling of the
WFPC2 Replacement Heater, with the bias anomalies occurring at the
temperature peaks. The other three CCDs {PC1, WF2, and WF3} appear to be
unaffected and continue to operate properly. Lowering the Replacement Heater
temperature set points by a few degrees C effectively eliminates the WF4
anomaly. On 9 January 2006, the upper set point of the WFPC2 Replacement
Heater was reduced from 14.9C to 12.2C. On 20 February 2006, the upper set
point was reduced from 12.2C to 11.3C, and the lower set point was reduced
from 10.9C to 10.0C. These changes restored the WF4 CCD bias level; however,
the bias level has begun to trend downwards again, mimicking its behavior in
late 2004 and early 2005. A third temperature reduction is planned for March
2007. We will reduce the upper set point of the heater from 11.3C to 10.4C
and the lower set point from 10.0C to 9.1C. The observations described in
this proposal will test the performance of WFPC2 before and after this
temperature reduction. Additional temperature reductions may be needed in
the future, depending on the performance of WF4. Orbits: internal 26,
external 1

FLIGHT OPERATIONS SUMMARY:

Significant Spacecraft Anomalies: (The following are preliminary reports of
potential non-nominal performance that will be investigated.)

HSTARS:

10757 - GSAcq(2.3.2) results in Fine Lock Back-up (2,0,2) using FGS-1

At 087/02:13:56 GSAcq (2,3,2) scheduled from 02:10:10-02:17:24 resulted in
Fine Lock Back-up (2,0,2) using FGS 1.
OBAD #1 RSS: 1783.55
OBAD #2 RSS: 8.39

COMPLETED OPS REQUEST:
18024-2 - ACS Bus C On-Orbit Test, Phase I - Part 1
18025-2 - ACS Bus C On-Orbit Test, Phase I - Part 2
18026-6 - ACS Bus C On-Orbit Test, Phase I - Part 3
18027-3 - ACS Bus C On-Orbit Test, Phase I - Part 4
18029-0 - Patch WF2 UIDLE replacement htr set point, adjustment #3


COMPLETED OPS NOTES:
1585-1 - Update WF-2 Temp Limits
1582-0 - Change JERRCNT Limit after Replacement Heater adj#3

SCHEDULED SUCCESSFUL
FGS GSacq 06 06

FGS REacq 00 00

OBAD with Maneuver 12 12

SIGNIFICANT EVENTS:

Flash Report: ACS Main Bus C On-orbit Test

As of 086/14:05:20 UTC, all commanding for the ACS Main Bus C on-orbit test
has been successfully completed through execution of Ops Requests 18024 -
18028. During the course of execution of Macro 3 to close the ACS Side 2
Hold relay for 50 ms, the PDU2 fuse was observed to clear, indicating the
likely location for the short circuit is in the Hold bus. The engineering
team is now reviewing the high-rate T-Prime telemetry data collected during
the test for a detailed analysis of the results. The primary Main Bus C
relay has been successfully re-opened, the FHSTs have been powered on, and
the remaining vehicle configuration has been restored to normal as part of
the post-test clean-up.

Flash Report: ACS Bus C Test, Post-Test Monitoring

The Fixed-Head Star Trackers are performing nominally following their power
cycle as part of the ACS Main Bus C test. OBAD corrections of approximately
0.5 and 0.005 degrees RSS were performed prior to the successful guide star
acquisition at 086/20:58.

Flash Report: WF/PC-II CCD4 replacement Heater In-Flight Temperature
Adjustment #3

The 3rd in-flight adjustment of the WF/PC-II replacement heater temperature
control was successfully completed with the execution of Ops Request 18029-0
at 086/18:20. All activities proceeded nominally.

The NSSC-1 executive limit table action value for the pyramid bulkhead
temperature was changed from 8.13 to 2.38 degC in accordance with the
updates to CARD item 2.4.6.1, and the UIDLE dead band control range was
shifted from 9.99 - 11.3 to 8.7 to 9.99 degC. The behavior of the
replacement heaters under the control of UIDLE and the optical bench
temperatures will continue to be monitored in real-time until such time as
the new settings can be functionally verified, likely within the next hour.
Another Flash Report will be sent following this verification.

Flash Report: Post WF/PC-II CCD4 Replacement Heater In-Flight Temperature
Adjustment #3 Monitoring

At 86/23:08 the replacement heaters were observed turning on when Bay1 fell
to 8.74 degs, ~ 7 minutes later they were disables when Bay1 reached 9.99
deg as expected, functionally verifying the patch.