Daily Report #4389

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 # 4389

PERIOD COVERED: UT June 21, 2007 (DOY 172)

OBSERVATIONS SCHEDULED

WFPC2 10877

A Snapshot Survey of the Sites of Recent, Nearby Supernovae

During the past few years, robotic {or nearly robotic} searches for
supernovae {SNe}, most notably our Lick Observatory Supernova Search {LOSS},
have found hundreds of SNe, many of them in quite nearby galaxies {cz 4000
km/s}. Most of the objects were discovered before maximum brightness, and
have follow-up photometry and spectroscopy; they include some of the
best-studied SNe to date. We propose to conduct a snapshot imaging survey of
the sites of some of these nearby objects, to obtain late-time photometry
that {through the shape of the light and color curves} will help reveal the
origin of their lingering energy. The images will also provide
high-resolution information on the local environments of SNe that are far
superior to what we can procure from the ground. For example, we will obtain
color-color and color-magnitude diagrams of stars in these SN sites, to
determine the SN progenitor masses and constraints on the reddening.
Recovery of the SNe in the new HST images will also allow us to actually
pinpoint their progenitor stars in cases where pre- explosion images exist
in the HST archive. This proposal is an extension of our successful Cycle 13
snapshot survey with ACS. It is complementary to our Cycle 15 archival
proposal, which is a continuation of our long-standing program to use
existing HST images to glean information about SN environments.

ACS/SBC 10810

The Gas Dissipation Timescale: Constraining Models of Planet Formation

We propose to constrain planet-formation models by searching for molecular
hydrogen emission around young {10-50 Myr} solar-type stars that have
evidence for evolved dust disks. Planet formation models show that the
presence of gas in disks is crucial to the formation of BOTH giant and
terrestrial planets, influences dust dynamics, and through tidal
interactions with giant planets leads to orbital migration. However, there
is a lack of systematic information on the presence and lifetime of gas
residing at planet-forming radii. We will use a newly identified broad
continuum emission feature of molecular hydrogen at 1600 Angstrom to search
for residual gas within an orbital radius of 5-10 AU around young stars that
have evolved beyond the optically thick T Tauri phase. These observations
will enable the most sensitive probe to date of remant gas in circumstellar
disks, detecting surfaces densites of ~0.0001 g/cm^2, or less than 10^-5 of
the theoretical "mininum mass" solar nebula from which our solar system is
thought to have formed. Our observations are designed to be synergistic with
ongoing searches for gas emission that is being performed using the Spitzer
Space Telescope in that the proposed HST observations are ~100 times more
sensitive and will have 50 times higher angular resolution. These combined
studies will provide the most comprehensive view of residual gas in
proto-planetary disks and can set important constraints on models of planet
formation.

WFPC2 10886

The Sloan Lens ACS Survey: Towards 100 New Strong Lenses

As a continuation of the highly successful Sloan Lens ACS {SLACS} Survey for
new strong gravitational lenses, we propose one orbit of ACS-WFC F814W
imaging for each of 50 high-probability strong galaxy-galaxy lens
candidates. These observations will confirm new lens systems and permit
immediate and accurate photometry, shape measurement, and mass modeling of
the lens galaxies. The lenses delivered by the SLACS Survey all show
extended source structure, furnishing more constraints on the projected lens
potential than lensed-quasar image positions. In addition, SLACS lenses have
lens galaxies that are much brighter than their lensed sources, facilitating
detailed photometric and dynamical observation of the former. When confirmed
lenses from this proposal are combined with lenses discovered by SLACS in
Cycles 13 and 14, we expect the final SLACS lens sample to number 80--100:
an approximate doubling of the number of known galaxy-scale strong
gravitational lenses and an order-of-magnitude increase in the number of
optical Einstein rings. By virtue of its homogeneous selection and sheer
size, the SLACS sample will allow an unprecedented exploration of the mass
structure of the early-type galaxy population as a function of all other
observable quantities. This new sample will be a valuable resource to the
astronomical community by enabling qualitatively new strong lensing science,
and as such we will waive all but a short {3-month} proprietary period on
the observations.

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.

NIC1/NIC2/NIC3 8794

NICMOS Post-SAA calibration - CR Persistence Part 5

A new procedure proposed to alleviate the CR-persistence problem of NICMOS.
Dark frames will be obtained immediately upon exiting the SAA contour 23,
and every time a NICMOS exposure is scheduled within 50 minutes of coming
out of the SAA. The darks will be obtained in parallel in all three NICMOS
Cameras. The POST-SAA darks will be non- standard reference files available
to users with a USEAFTER date/time mark. The keyword 'USEAFTER=date/time'
will also be added to the header of each POST-SAA DARK frame. The keyword
must be populated with the time, in addition to the date, because HST
crosses the SAA ~8 times per day so each POST-SAA DARK will need to have the
appropriate time specified, for users to identify the ones they need. Both
the raw and processed images will be archived as POST-SAA DARKSs. Generally
we expect that all NICMOS science/calibration observations started within 50
minutes of leaving an SAA will need such maps to remove the CR persistence
from the science images. Each observation will need its own CRMAP, as
different SAA passages leave different imprints on the NICMOS detectors.

NIC3 10792

Quasars at Redshift z=6 and Early Star Formation History

We propose to observe four high-redshift quasars {z=6} in the NIR in order
to estimate relative Fe/Mg abundances and the central black hole mass. The
results of this study will critically constrain models of joint quasar and
galaxy formation, early star formation, and the growth of supermassive black
holes. Different time scales and yields for alpha-elements {like O or Mg}
and for iron result into an iron enrichment delay of ~0.3 to 0.6 Gyr. Hence,
despite the well-known complexity of the FeII emission line spectrum, the
ratio iron/alpha - element is a potentially useful cosmological clock. The
central black hole mass will be estimated based on a recently revised back
hole mass - luminosity relationship. The time delay of the iron enrichment
and the time required to form a supermassive black hole {logM8 Msol, tau
~0.5Gyr} as evidenced by quasar activity will be used to date the beginning
of the first intense star formation, marking the formation of the first
massive galaxies that host luminous quasars, and to constrain the epoch when
supermassive black holes start to grow by accretion.

NIC3 11080

Exploring the Scaling Laws of Star Formation

As a variety of surveys of the local and distant Universe are approaching a
full census of galaxy populations, our attention needs to turn towards
understanding and quantifying the physical mechanisms that trigger and
regulate the large-scale star formation rates {SFRs} in galaxies.

NIC3 10504

Characterizing the Sources Responsible for Cosmic Reionization

Our group has demonstrated the role that massive clusters, acting as
powerful cosmic lenses, can play in constraining the abundance and
properties of low-luminosity star- forming sources beyond z~6; such sources
are thought to be responsible for ending cosmic reionization. The large
magnification possible in the critical regions of well- constrained clusters
brings sources into view that lie at or beyond the limits of conventional
exposures such as the UDF, as well as those in imaging surveys being
undertaken with IRAC onboard Spitzer. We have shown that the combination of
HST and Spitzer is particularly effective in delivering the physical
properties of these distant sources, constraining their mass, age and past
star formation history. Indirectly, we therefore gain a valuable glimpse to
yet earlier epochs. Recognizing the result {and limitations} of the UDF
exposure, we propose a systematic search through 6 lensing clusters with ACS
and NICMOS for further z~6-7 sources in conjunction with existing deep IRAC
data. Our survey will mitigate cosmic variance and extend the search both to
lower luminosities and, by virtue of the NICMOS/IRAC combination, to higher
redshift. The goal is to count and characterize representative sources at
z~6-10 and to delineate the redshift range of activity for the planning of
future observations.

WFPC2 10807

The knotty jet of He 2-90: An ideal laboratory for studying the formation
and propagation of jets in dying stars

Previous WFPC2 observations have led to the serendipitous discovery of an
extended, highly-collimated, ``pulsed" bipolar jet emanating from a compact
planetary nebula, He 2- 90. Subsequently, an average proper motion of the
knots in the jet was measured, which together with radial velocities,
enabled us to characterise the basic physical properties of the jet. The
knotty jet in He 2-90 resembles other prominent examples of pulsed jets in
young stellar objects or symbiotic stars, but is probably by far the best
example yet of a non-relativistic, symmetric, jet in a ``clean"
astrophysical environment. The formation {acceleration and collimation} of
jets is not fully understood, specially in the case of jets in dying stars.
We now propose to re-image He 2-90 with WFPC2 and exploit the factor 3.5
longer time baseline now available from the first-epoch observations in
September 1999, in order to measure the proper motion of individual knots in
the jet with unprecedented accuracy. These data will enable us to
characterise the ejection history of the source, specially deviations from a
constant period {latter is related to the binary period of the system},
e.g., due to instabilities in the accretion mechanism. We will also be able
to test if the ejection mechanism is symmetric: any deviation in the
ejection history of the knots in the opposing jet beams, will indicate a
magnetic field structure and/or the accretion disk which is not symmetric
across the equatorial plane. We will also carry out deep imaging with the
ACS/WFC camera in order to determine the shapes/sizes of a large number of
knots. The shapes/sizes of the knots, and changes with distance from the
source probe the strength of the magnetic field inside the jet. HRC imaging
of the central source and jet on sub-arcsecond scales will be carried out to
probe the magnetic field close to the jet source, and deviations from
linearity in the jet-beam which may result from instabilities in the
magnetic field. These data will allow us to significantly improve our
existing 2- dimensional MHD model of the He2-90 jet, and/or provide impetus
for new 3-dimensional models.

WFPC2 10900

Optical polarimetry of PSR B0540-69 and its synchrotron nebula.

Polarization measurements of pulsars and of their synchrotron nebulae are
uniquely able to provide deep insights into the highly magnetized
relativistic environment of young rotating neutron stars. Apart from the
radio band, pulsar polarization is best measured in the optical, for the
rare cases of detectable optical emission. One of the brightest pulsars
together with Crab {PSR B0531+21} and Vela {PSR B0833-45}, for which optical
polarization measurements support the newly developed two-pole caustic model
{TPC}, is PSR B0540-69 in the Large Magellanic Clouds, often referred as the
Crab Twin for their overall similarities in both age and energetics.
Together with the Crab, PSR B0540-69 is also the only pulsar embedded in a
synchrotron nebula visible at optical wavelengths. We plan to observe PSR
B0540-69 and its compact nebula {4 arcsec diameter} with the Advanced Camera
for Surveys {ACS} and the Wide Field Channel {WFC} detector using UV and
visual polarization filters. Thanks to the superb angular resolution of ACS,
these observations will allow us to spectacularly resolve the pulsar from
its nebular background, providing the first firm measure of the pulsar
polarization which will be crucial to assess, on a broader sample, the
validity of the TPC model with respect to other pulsars magnetosphere
models. These observations will also provide the first detailed polarization
map of the nebula, including the jet and the torus seen in our previous
WFPC2 images.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS: (None)

COMPLETED OPS REQUEST:

18105-1 - MSS/CSS Gyro2 Converged & Remove Gyro2 Test#37.
18054-0 - Preview KF Sun Vector Data via Telemetry Diags.
18108-1 - PCS KF OOT Support.
18109-1 - PCS KF OOT Support.
18106-0 - MSS/CSS Converged Add/Remove Gyro1Tests#19&#23.
18054-0 - Preview KF Sun Vector Data via Telemetry Diags.

SCHEDULED SUCCESSFUL

FGS GSacq 09 09
FGS REacq 04 04
OBAD with Maneuver 26 26

COMPLETED OPS NOTES: (None)

SIGNIFICANT EVENTS:

Evaluation of Universal Kalman Filter performance continued. Multiple text
segments were executed, all of them successfully. Details follow

The filter was configured to disable the CSS input at 172/14:09, leaving
only the MSS input enabled. The Gyro 2 sensor input was added to the
converged KF filter at 172/14:20. The gyro input was added during a vehicle
slew and during a fast changing B-field. All UKF parameters showed nominal
operation. The test was to monitor the addition of the Gyro2 sensor input
into an MSS only converged filter (M_G2_RVF, Test #37). The Gyro2 input was
removed at 172/14:41, leaving only the MSS sensor input enabled.

The Gyro1 sensor input was added to the converged KF filter at 172/19:48.
The filter was configured to use only the MSS input. The gyro input was
added during a vehicle slew and a fast changing B-field. All UKF parameters
showed nominal operation. The test was to monitor the addition of the Gyro1
sensor input into an MSS only converged filter (M_G1_RVF, Test #19). The
Gyro1 input was later removed at 172/21:32 during a vehicle slew and a fast
changing B-field. The removal of the Gyro1 input completed the second part
of the Ops Request (M_G1_HVF, Test #23). Again, all UKF parameters showed
nominal operation. The removal of the Gyro1 input leaves the KF configured
to use MSS sensor input only.

The test above completes the KF Convergence testing. Two long-term tests
remain to configure the KF for MSS/Gyro2 and MSS/CSS/Gyro2 for one week
each.