HUBBLE SPACE TELESCOPE - Continuing to collect World Class
Science
DAILY REPORT #4822
PERIOD COVERED: 5am March 30 - 5am March 31, 2009 (DOY
089/0900z-090/0900z)
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 11302
WFPC2 CYCLE 16 Standard Darks - Part III
This dark calibration program obtains dark frames every
week in order to
provide data for the ongoing calibration of the CCD dark
current rate,
and to monitor and characterize the evolution of hot
pixels. Over an
extended period these data will also provide a monitor of
radiation
damage to the CCDs.
WFPC2 11793
WFPC2 Cycle 16 Internal Monitor
This calibration proposal is the Cycle 15 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 (both
gain 7 and
gain 15 -- to test stability of gains and bias levels), a
test for
quantum efficiency in the CCDs, and a monitor for possible
buildup of
contaminants on the CCD windows. These also provide raw
data for
generating annual super-bias reference files for the
calibration
pipeline.
WFPC2 11593
Dynamical Masses of the Coolest Brown Dwarfs
T dwarfs are excellent laboratories to study the evolution
and the
atmospheric physics of both brown dwarfs and extrasolar
planets. To
date, only a single T dwarf binary has a dynamical mass
determination,
and more are sorely needed. The prospects of measuring
more dynamical
masses over the next decade are limited to 6 known
short-period T dwarf
binaries. We propose here to obtain Long-Term HST/ACS
monitoring for the
3 of the 6 binaries which cannot be resolved with AO from
the ground.
Upon completion, our program will substantially increase
the number of T
dwarf dynamical mass measurements and thereby provide key
benchmarks for
testing theoretical models of ultracool objects.
WFPC2 11944
Binaries at the Extremes of the H-R Diagram
We propose to use HST/Fine Guidance Sensor 1r to survey
for binaries
among some of the most massive, least massive, and oldest
stars in our
part of the Galaxy. FGS allows us to spatially resolve
binary systems
that are too faint to observe using ground-based, speckle
or optical
long baseline interferometry, and too close to resolve
with AO. We
propose a SNAP-style program of single orbit FGS TRANS
mode observations
of very massive stars in the cluster NGC 3603, luminous
blue variables,
nearby low mass main sequence stars, cool subdwarf stars,
and white
dwarfs. These observations will help us to (1) identify
systems suitable
for follow up studies for mass determination, (2) study
the role of
binaries in stellar birth and in advanced evolutionary
states, (3)
explore the fundamental properties of stars near the main
sequence-brown
dwarf boundary, (4) understand the role of binaries for
X-ray bright
systems, (5) find binaries among ancient and nearby
subdwarf stars, and
(6) help calibrate the white dwarf mass - radius relation.
WFPC2 11974
High-resolution Imaging for 9 Very Bright,
Spectroscopically Confirmed,
Group-scale Lenses
There are large samples of strong lenses that probe small
(galaxy) scale
masses (e.g., SLACS, SQLS, COSMOS). There are also large
samples of
strong lenses that probe large (rich cluster) scale masses
(e.g.,
various rich Abell clusters, the Hennawi et al. 2008 SDSS
sample). The
sample of strong lenses that probe intermediate
(group/cluster-core)
scale masses, however, is sparse, and so any significant
additions to
this sample are important. Here we present a sample of
strong lenses
that not only probe these intermediate scales but are also
quite bright,
since the sample is based almost entirely upon data from
the SDSS, a
relatively shallow and poor-resolution survey, at least in
comparison to
most other strong lens hunting grounds, such as COSMOS and
CFHTLS. What
we lack are the high-resolution imaging data needed to
construct
detailed lensing models, to probe the mass and light
profiles of the
lensing galaxies and their environments, and to
characterize the
morphologies of the lensed (source) galaxies. Only HST can
provide these
data, and so we are proposing here for 81 orbits of deep
WFPC2 F450W,
F606W and F814W imaging, for 9 of our best and brightest
intermediate-scale lensing systems with known
spectroscopic redshifts
and with Einstein radii between 4 and 8 arcsec.
WFPC2 11977
WFPC2 12-Year Proper Motions of Two Galactic Analogs of
the SN1987A
Rings
This special call in Cycle 16 is a unique opportunity to
measure
fine-scale proper motions with the same WFPC2 camera after
more than a
decade has elapsed, and is the last time such an
opportunity is likely
to be available. We aim to apply this powerful tool to the
ring nebulae
around two hot supergiants: the set of ionized
double-rings around the
massive eclipsing binary RY Scuti, and the equatorial ring
and bipolar
lobes around Sher 25. These are the only two Galactic
analogs of SN1987A
for which this proper motion measurement is possible
(others lack a
first-epoch image with HST, and SN1987A is too distant).
In the case of
RY Scuti, the expected motions are small because the
compact ring nebula
is only 1-arcsec in diameter. For Sher 25 the expected
motions are small
because the object is thought to be at d=6 kpc. The 10-12
years that
have elapsed since earlier imaging epochs for these
sources make it
possible to accurately measure their expected sub-pixel
proper motion,
and hence, their ages and distances. We can discriminate
between
specific proposed models for the formation of these ring
nebulae by
measuring the relative ages of these ionized equatorial
rings compared
to outer structures: the bipolar lobes in the case of Sher
25, and an
outer dust shell in the case of RY Scuti. These will
provide the first
quantitative tests of binary merger vs. rapidly rotating
single star
models for the shaping of SN1987A and related ring nebulae
around
massive stars, which until now have relied upon
qualitative comparisons
to structues seen in single-epoch images. The expected
expansion is less
than 0.1 arcsec, so there is no hope of making either
measurement from
the ground, and increased systematic errors associated
with switching to
new instruments (with different pixel scales and
distortion corrections)
will make this measurement more difficult even for HST
after SM4.
FLIGHT OPERATIONS SUMMARY:
Significant Spacecraft Anomalies: (The following are
preliminary reports
of potential non-nominal performance that will be
investigated.)
HSTARS:
11747 - GSAcq(1,2,1) at 089/13:08:31 and REAcq(1,2,1) at
089/14:22:48
both failed to fine lock backup on FGS 1.
Observations possibly affected: WFPC 23 - 30, Proposal ID# 11977.
11748 - GSAcq(1,3,1)scheduled for 090/00:28:00 failed due
search radius
limit exceeded on FGS1 at 090/00:32:54.
REAcq(1,3,1) scheduled for 090/00:57:01 failed due search radius limit
exceeded on FGS1 at 090/01:01:45.
Observation affected: WFPC 37 - 39, Proposal ID# 11593
11749 - GSAcq(2,3,2) scheduled from 090/05:25:47 -
05:33:52 resulted in
fine lock backup (2,0,2) using FGS-2 due to (QF3STOPF) and (QSTOP) stop
flag indications on FGS-3.
Observation possibly affected: Astrometry Proposal ID# 11944.
COMPLETED OPS REQUEST: (None)
COMPLETED OPS NOTES: (None)
SCHEDULED
SUCCESSFUL
FGS
GSAcq
06
05
FGS
REAcq
06
05
OBAD with Maneuver
18
18
SIGNIFICANT EVENTS: (None)