HUBBLE SPACE TELESCOPE - Continuing to collect World Class
Science
DAILY REPORT #4800
PERIOD COVERED: 5am February 26 - 5am February 27, 2009
(DOY
057/1000z-058/1000z)
OBSERVATIONS SCHEDULED
ACS/SBC 11982
Spanning the Reionization History of IGM Helium: a Large
and Efficient
HST Spectral Survey of Far-UV-Bright Quasars
The reionization of IGM helium is thought to have occurred
at redshifts
of z=3 to 4. Detailed studies of HeII Lyman-alpha
absorption toward a
handful of QSOs at 2.7<z<3.3 demonstrated the high
potential of such IGM
probes, but the small sample size and redshift range limit
confidence in
cosmological inferences. The requisite unobscured
sightlines to high-z
are extremely rare, but we've cross-correlated 10, 000
z>2.8 SDSS DR7
(and other) quasars with GALEX GR4 UV sources to obtain
550 new, high
confidence, sightlines potentially useful for HST HeII
studies; and in
cycle 15-16 trials we demonstrated the efficacy of our
SDSS/GALEX
selection approach identifying 9 new HeII quasars at
unprecedented 67%
efficiency. We propose the first far-UV-bright HeII quasar
survey that
is both large in scale and also efficient, via 2-orbit
reconnaissance
ACS/SBC prism spectra toward a highly select subset of 40
new SDSS/GALEX
quasars at 3.1<z<5.1. These will provide a community
resource list that
includes 5 far-UV-bright (restframe) HeII sightlines in
each of 8
redshift bins spanning 3.1<z<3.9 (and perhaps
several objects at z>4),
enabling superb post-SM4 follow-up spectra with COS or
STIS. But
simultaneously and independent of any SM4 uncertainties,
we will hereby
directly obtain 10-orbit UV spectral stacks from the 5
HeII quasars in
each of the 8 redshift bins to trace the reionization
history of IGM
helium over at least
3.1<z<3.9. These spectral stacks will average over
cosmic variance and individual object pathology. Our new
high-yield HeII
sightline sample and spectral stacks, covering a large
redshift range,
will allow confident conclusions about the spectrum and
evolution of the
ionizing background, the evolution of HeII opacity, the
density of IGM
baryons, and the epoch of helium reionization.
WFPC2 11972
Investigating the Early Solar System with Distant Comet
Nuclei
We propose 85 orbits of imaging observations with the
WFPC2 to get
nucleus size estimates for 8 well observed dynamically new
and
long-period comets at large distances from the sun when
their activity
levels are low. This will increase the sample of these
nucleus sizes by
nearly 50%, but will more than double the selection of
comets for which
we can run thermal models. Small icy bodies are the best
preserved
remnants of planet formation, and we have recently found
that
observationally constrained thermal models can distinguish
differences
in microphysical properties of comet nuclei. The new HST
data will
enable the first exploration of physical conditions in
different regions
of the early solar nebula.
WFPC2 11978
Luminous and Dark Matter in Disk Galaxies from Strong
Lensing and
Stellar Kinematics
The formation of realistic disk galaxies within the LCDM
paradigm is
still an unsolved problem. Theory is only now beginning to
make
predictions for how dark matter halos respond to galaxy
formation and
for the properties of disk galaxies. Measuring the density
profiles of
dark matter halos on galaxy scales is therefore a strong
test for the
standard paradigm of galaxy formation, offering great
potential for
discovery. However, from an observational point of view,
the degeneracy
between the stellar and dark matter contributions to
galaxy rotation
curves remains a major road block. Strong gravitational
lensing, when
coupled to spatially-resolved kinematics and stellar
population models,
can solve this long-standing problem. Unfortunately, this joint
methodology could not be exploited so far due to the
paucity of known
edge-on spiral lenses. Exploiting the full SDSS-DR7
archive we have
identified a new sample of exactly these systems. We
propose multi-color
HST imaging to confirm and measure a sample of twenty
spiral lenses,
covering a range of bulge to disk ratios. By combining
dynamical lensing
and stellar population information for this unique sample
we will
deliver the first statistical constraints on halos and
disk properties,
and a new stringent test of disk galaxy formation
theories.
WFPC2 11983
An Imaging Survey of Protoplanetary Disks and Brown Dwarfs
in the
Chamaeleon I region
We propose to carry out a HST/WFPC2 survey of young brown
dwarfs, Class
I and Class II sources in the Chamaelon I region, one of
the
best-studied star-forming regions, in order to investigate
the link
between disk evolution and the formation of
substellar-mass objects. We
will use deep broad-band imaging in the I and z-equivalent
HST bands to
unveil the unknown population of substellar binary
companions, down to a
few Jupiter masses for separations of a few tens of AU. We
will also
perform narrow-band imaging to directly detect accreting
circumstellar
disks and jets around brown dwarfs, Class-I and class-II objects.
Chamaelon I is nearly coeaval of Orion (~1-2Myr) but at
~1/3 its
distance, allowing 3x higher resolution and 10x more flux
for comparable
objects. Unlike Orion, low-mass objects and protoplanetary
disks in
Chamaeleon I have been extensively studied with Spitzer,
but not yet
with the HST. The Chamaeleon I region is an ideal HST
target, as it lies
in the CVZ of the HST and therefore it is easily
accessible any time of
the year with long orbits.
WFPC2 11986
Completing HST's Local Volume Legacy
Nearby galaxies offer one of the few laboratories within
which stellar
populations can be tied to multi-wavelength observations.
They are thus
essential for calibrating and interpreting key
astrophysical
observables, such as broad-band luminosities, durations
and energy input
from starbursts, and timescales of UV, H-alpha, and FIR
emission. The
study of stellar populations in nearby galaxies requires
high-resolution
observations with HST, but HST's legacy for this limited
set of galaxies
remains incomplete.
As a first attempt to establish this legacy, The ACS
Nearby Galaxy
Survey Treasury (ANGST) began observations in late 2006.
ANGST was
designed to carry out a uniform multi-color survey of a
volume-limited
sample of ~70 nearby galaxies that could be used for
systematic studies
of resolved stellar populations. The resulting data
provide nuanced
constraints on the processes which govern star formation
and galaxy
evolution, for a well-defined population of galaxies. All
photometry for
the survey has been publicly released.
However, the failure of ACS 4.5 months after ANGST began
taking data led
to a drastic reduction in the planned survey. The loss is
two-fold.
First, the goals of completeness and uniformity were
greatly
compromised, impacting global comparison studies. Second,
the variety of
observed star formation histories was reduced. Given that
we have never
found two galaxies with identical star formation
histories, and fully
sampling the population allows us to catch those few
systems whose star
formation rates and metallicities place the strongest
constraints on key
astrophysical processes.
Here we propose WFPC2 observations of all remaining
galaxies within the
Local Volume (D<3.5Mpc) for which current HST
observations are
insufficient for meaningful stellar population studies. We
will use
these observations for research on the star formation
histories of
individual galaxies and the Local Volume, detailed
calibrations of star
formation rate indicators, and the durations of
starbursts. We will also
make them publicly available through the ANGST archive to
support future
research. The proposed observations will finally complete
a lasting
legacy of HST
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: (None)
COMPLETED OPS NOTES: (None)
SCHEDULED
SUCCESSFUL
FGS
GSAcq
05
05
FGS
REAcq
05
05
OBAD with Maneuver
20
20
SIGNIFICANT EVENTS: (None)