NASA Hubble Space Telescope Daily Report # 3761
HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science
DAILY REPORT # 3761
PERIOD COVERED: DOY 356
OBSERVATIONS SCHEDULED
ACS/HRC 10165
Determination of orbits and colors for two new binaries in the Koronis
asteroid family
We propose to measure color and orbital properties of two asteroid
binaries in the Koronis family discovered in our SNAP-9747 survey. The
best previously studied asteroid binary system, Ida/Dactyl, is also in
the Koronis family. Differential space weathering measured on the Ida
and Dactyl surfaces has been a powerful constraint on models of
satellite formation mechanisms and satellite survivability. HST offers
the unique opportunity for similar measurements of these much smaller,
main-belt binaries. The new satellites are believed to have formed
through different collisional mechanisms than Ida/Dactyl. Further,
with a set of 4 relative position measurements for each of the two
systems, added to the discovery snapshots, we will determine and
compare the densities of the primaries with Ida {a large, 31.5 km,
asteroid with density 2.6+-0.5 g/cm^3, measured by the Galileo flyby}.
In contrast, {17246} and {22899} are 4.5 km bodies that are likely to
have been restructured since the family-forming event by subsequent
collisions. As all are members of the same family, differences in
density would constrain bulk composition and internal structure {e.g.
shard vs. rubble-pile}. Hence, these measurements are likely to
further elucidate the mechanisms for formation of satellites.
ACS/HRC 10391
Wavelength and Flux Calibration of the ACS prisms
The wavelength calibration of the SBC {PR110L and PR130L} and HRC
{PR200L} prisms will be established by observing a planetary nebula in
the LMC and QSOs at carefully selected redshifts. Flux calibrations
will be derived for each prism by observing white dwarf standards.
ACS/WFC/WFPC2 10265
The Formation History of Andromeda
We propose deep observations of Andromeda’s outer disk and giant tidal
stream, to reconstruct their star formation histories. As the nearest
giant galaxy, Andromeda offers the best testing ground for
understanding galaxy formation and evolution. Given the dramatic
increase in sensitivity offered by the ACS, we can now resolve stars
on the old main sequence in the other giant spiral of the Local Group,
and employ the same direct age diagnostics that have been used for
decades in the study of Galactic globular clusters. In Cycle 11, we
successfully observed a field in the Andromeda halo and constructed a
deep color-magnitude diagram reaching well below the oldest main
sequence turnoff. In Cycle 13, we propose to extend these observations
to the outer disk and tidal stream of Andromeda, to constrain their
star formation histories and compare them to that of the halo. The
combined observations from these two programs will offer a dramatic
advance in our understanding of the overall evolution of spiral
galaxies.
ACS/WFC/WFPC2 9392
The Ancient Stars of M32
The question of whether the dwarf elliptical galaxy M32 contains a
population of truly ancient stars has remained unsettled for decades.
We recently used HST/WFPC2 to identify for the first time a population
of RR Lyr stars in this galaxy. Since these stars are known only to be
present in stellar populations older than 8-10 Gyr, we contend that
M32 does possess an old stellar component and certainly cannot be
comprised of only intermediate-age {~ 5 Gyr} stars as has been
frequently suggested in the literature. Our earlier observations were
insufficient to determine even the most basic photometric properties
of these stars. Nor could we use the data to identify independent
evidence of the old population that could help constrain just what
fraction of the galaxy’s stars are ancient. We propose new HST/ACS
observations to {a} get periods and luminosities of the previously
observed RR Lyr stars, {b} search for additional RR Lyr stars in a
significantly larger volume of M32, and {c} obtain ultra-deep 2-color
photometry to study the ancient main-sequence turnoff region of that
galaxy directly, {d} look for radial population gradients in M32, both
among the RR Lyr/Horizontal Branch and main- sequence populations, {e}
compare the M31/M32 old populations in terms of metallicity spread,
and {f} use the RR Lyr stars to precisely determine the relative and
possibly the absolute distances of M32 and M31’s halo.
WFPC2 10132
UV Confirmation of New Quasar Sightlines Suitable for the Study of
Intergalactic Helium
The reionization of intergalactic helium is thought to have occurred
between redshifts of about 3 and 4. The study of HeII Lyman-alpha
absorption towards a half-dozen quasars at 2.7
emphasis on extending helium studies to the highest redshift
sightlines. Our proposed approach has already proven successful, and
additional sightlines will enable follow-up spectal observations to
measure the spectrum and evolution of the ionizing background
radiation, the density of intergalactic baryons, and the epoch of
reionization of the IGM.
WFPC2 10360
WFPC2 CYCLE 13 INTERNAL MONITOR
This calibration proposal is the Cycle 13 routine internal monitor for
WFPC2, to be run weekly to monitor the health of the cameras. A
variety of internal exposures are obtained in order to provide a
monitor of the integrity of the CCD camera electronics in both bays
{gain 7 and gain 15}, a test for quantum efficiency in the CCDs, and a
monitor for possible buildup of contaminants on the CCD windows.
FLIGHT OPERATIONS SUMMARY:
Significant Spacecraft Anomalies: (The following are preliminary
reports of potential non-nominal performance that will be
investigated.) None
COMPLETED OPS REQs: None
OPS NOTES EXECUTED:
0900-1 COMMAND PROBLEM @ 357/08:36:25z
SCHEDULED SUCCESSFUL FAILURE TIMES FGS Gsacq 06 06 FGS Reacq 09 09 FHST Update 11 11 LOSS of LOCK
SIGNIFICANT EVENTS:
Secondary Mirror move scheduled first opportunity 357/23:12Z – 23:27Z
(OR 17352 with attached script). The STScI has requested a Secondary
Mirror move of +4 microns. Last Secondary Mirror move, a +3.6 micron
move, was executed 2000.336.
