HUBBLE SPACE TELESCOPE - Continuing to collect World Class
Science
DAILY REPORT #4806
PERIOD COVERED: 5am March 6 - 5am March 9, 2009 (DOY
065/1000z-068/1000z)
OBSERVATIONS SCHEDULED
ACS/SBC 11984
Observing Saturn's High Latitude Polar
Planetary auroral emissions are critical indicators of how
the
magnetospheres of the planets work. Recently, a new
component of
Saturn's auroral emissions, i.e. high latitude auroras
inside the main
auroral oval, have been observed by the Cassini spacecraft
during
otherwise quiet auroral conditions. Such high latitude
auroras are of
immense interest since they occur on magnetic flux tubes
connected to a
region that is key to the overall dynamics of the system,
the
magnetotail, and where if conventional theories regarding
Saturn's
magnetosphere are correct there should not be any auroras.
These faint
auroral emissions have not been previously observed by the
Hubble Space
Telescope (HST). However, the unique oblique viewing
geometry afforded
during early 2009 due to Saturn's orbital longitude will
result in the
apparent brightening of these polar emissions due to the
limb-brightening effect, with the result that they may be
observable by
HST for the first ever time. In addition, at this time the
Cassini
spacecraft will be in a high latitude orbit, with a
trajectory that will
take it through these magnetic flux tubes, providing
essential
simultaneous in situ data. This is the last time Cassini
will be in such
an orbit during its mission as currently scheduled and HST
is the only
instrument capable of obtaining sustained long-term
observations of
Saturn's auroras. These observations will address the
following:
Does Saturn exhibit high latitude UV auroras observable by
HST? Where do
these auroras occur, and at what altitude? How do these
auroras behave
over time? How variable are they? Are they periodic? How
do they behave
with respect to other auroral components? What processes
drive these
auroras?
Are these auroras generated by processes internal to the
magnetosphere
or are they driven by the solar wind? How do the infrared
(IR) auroras
relate to the ultraviolet (UV) auroras?
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.
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 11981
FUV Imaging Survey of Galactic Open Clusters
We propose a WFPC2 FUV imaging survey of 6 Galactic open
clusters with
ages ranging from 1 Myr to 300 Myr complemented with
NUV/optical imaging
of the same fields. No such survey has ever been attempted
before in the
FUV at the resolution of WFPC2 (indeed, no WFPC2 FUV
images of any
Galactic open cluster exist in the HST archive) and, since
WFPC2 will be
retired in SM4 and none of the other HST instruments can
do FUV imaging
of bright objects, this is the last chance to do such a
survey before
another UV telescope is launched. This survey will provide
a new
perspective on young/intermediate age Galactic clusters
and a key
template for the study of star formation at high redshift,
where the
intensity peak we observe in the optical/NIR from Earth is
located in
the FUV in its rest frame. For clusters still associated
with an H II
region, UV imaging maps the continuum emission of the
ionized gas and
the radiation scattered by background dust and, combined
with optical
nebular images, can be used to determine the 3-D structure
of the H II
region. For all young clusters, FUV+NUV+optical photometry
can be used
to study the UV excesses of T-Tauri stars. For clusters
older than ~40
Myr, the same photometric combination is the easiest
method to detect
companion white dwarfs which are invisible using only the
optical and
NIR. WFPC2 is also an excellent instrument to discover
close companions
around bright stars and improve our knowledge of their
multiplicity
fraction. Finally, for all clusters, the combination of
high-spatial-resolution UV and optical photometry can be
used to
simultaneously measure the temperature, extinction,
extinction law,
distance, and existence of companions (resolved and
unresolved) and,
thus, produce clean HR diagrams with resolved cluster
membership and
much-reduced systematic uncertainties.
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 11975
UV Light from Old Stellar Populations: a Census of UV
Sources in
Galactic Globular Clusters
In spite of the fact that HST has been the only operative
high-resolution eye in the UV-window over the last 18
years, no
homogeneous UV survey of Galactic globular clusters (GGCs)
has been
performed to date. In order to fill this gap in the
stellar population
studies, we propose a program that exploits the unique
capability of the
WFPC2 and the SBC in the far-/mid- UV for securing deep UV
imaging of 46
GGCs. The proposed observations will allow to study with
unprecedented
accuracy the hottest GGC stars, comprising the extreme
horizontal branch
(HB) stars and their progeny (the so-called AGB-manque',
and Post-early
AGB stars), and "exotic stellar populations"
like the blue straggler
stars and the interacting binaries. The targets have been
selected to
properly sample the GGC metallicity/structural parameter
space, thus to
unveil any possible correlation between the properties of
the hot
stellar populations and the cluster characteristics. In
addition, most
of the targets have extended HB "blue tails",
that can be properly
studied only by means of deep UV observations, expecially
in the far-UV
filters like the F160BW, that is not foreseen on the WFC3.
This data
base is complemented with GALEX observations in the
cluster outermost
regions, thus allowing to investigate any possible trend
of the
UV-bright stellar types over the entire radial extension
of the
clusters. Although the hottest GGC stars are just a small
class of
"special" objects, their study has a broad
relevance in the context of
structure formation and chemical evolution in the early
Universe,
bringing precious information on the basic star formation
processes and
the origin of blue light from galaxies. Indeed, the
proposed
observations will provide the community with an
unprecedented data set
suitable for addressing a number of still open
astrophysical questions,
ranging from the main drivers of the HB morphology and the
mass loss
processes, to the origin of the UV upturn in elliptical
galaxies, the
dating of distant systems from integrated light, and the
complex
interplay between stellar evolution and dynamics in dense
stellar
aggregates. In the spirit of constructing a community
resource, we
entirely waive the proprietary period for these
observations.
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.
FGS 11788
The Architecture of Exoplanetary Systems
Are all planetary systems coplanar? Concordance cosmogony
makes that
prediction. It is, however, a prediction of extrasolar
planetary system
architecture as yet untested by direct observation for
main sequence
stars other than the Sun. To provide such a test, we
propose to carry
out FGS astrometric studies on four stars hosting seven
companions. Our
understanding of the planet formation process will grow as
we match not
only system architecture, but formed planet mass and true
distance from
the primary with host star characteristics for a wide
variety of host
stars and exoplanet masses.
We propose that a series of FGS astrometric observations
with
demonstrated 1 millisecond of arc per-observation
precision can
establish the degree of coplanarity and component true
masses for four
extrasolar systems: HD 202206 (brown dwarf+planet); HD
128311
(planet+planet), HD 160691 = mu Arae (planet+planet), and
HD 222404AB =
gamma Cephei (planet+star). In each case the companion is
identified as
such by assuming that the minimum mass is the actual mass.
For the last
target, a known stellar binary system, the companion orbit
is stable
only if coplanar with the AB binary orbit.
FGS 11785
Trigonometric Calibration of the Distance Scale for
Classical Novae
The distance scale for classical novae is important for
understanding
the stellar physics of their thermonuclear runaways, their
contribution
to Galactic nucleosynthesis, and their use as
extragalactic standard
candles. Although it is known that there is a relationship
between their
absolute magnitudes at maximum light and their subsequent
rates of
decline--the well-known maximum-magnitude rate-of-decline
(MMRD)
relation--it is difficult to set the zero-point for the
MMRD because of
the very uncertain distances of Galactic novae.
We propose to measure precise trigonometric parallaxes for
the quiescent
remnants of the four nearest classical novae. We will use
the Fine
Guidance Sensors, which are proven to be capable of
measuring parallaxes
with errors of ~0.2 mas, well below what is possible from
the ground.
ACS/SBC 11579
The Difference Between Neutral- and Ionized-Gas Metal
Abundances in
Local Star-Forming Galaxies with
The metallicity of galaxies and its evolution with
redshift is of
paramount importance for understanding galaxy formation.
Abundances in
the interstellar medium (ISM) are typically determined
using
emission-line spectroscopy of HII regions. However, since
HII regions
are associated with recent SF they may not have abundances
typical for
the galaxy as a whole. This is true in particular for star-forming
galaxies (SFGs), in which the bulk of the metals may be
contained in the
neutral gas. It is therefore important to directly probe
the metal
abundances in the neutral gas. This can be done using
absorption lines
in the Far UV. We have developed techniques to do this in
SFGs, where
the absorption is measured for sightlines toward bright SF
regions
within the galaxy itself. We have successfully applied
this technique to
a sample of galaxies observed with FUSE. The results have
been very
promising, suggesting in I Zw 18 that abundances in the
neutral gas may
be up to 0.5 dex lower than in the ionized gas. However,
the
interpretation of the FUSE data is complicated by the very
large FUSE
aperture (30 arcsec), the modest S/N, and the limited
selection of
species available in the FUSE bandpass. The advent of
allows a significant advance in all of these areas. We
will therefore
obtain absorption line spectroscopy with G130M in the same
sample for
which we already have crude constraints from FUSE. We will
obtain
ACS/SBC images to select the few optimal sightlines to
target in each
galaxy. The results will be interpreted through
line-profile fitting to
determine the metal abundances constrained by the
available lines. The
results will provide important new insights into the
metallicities of
galaxies, and into outstanding problems at high redshift
such as the
observed offset between the metallicities of Lyman Break
Galaxies and
Damped Lyman Alpha systems.
FLIGHT OPERATIONS SUMMARY:
Significant Spacecraft Anomalies: (The following are
preliminary reports
of potential non-nominal performance that will be
investigated.)
HSTARS:
11709 - REAcq (1,2,2) failed due to Scan Step Limit
Exceeded on FGS-1 @
067/01:08:53z
Observations affected: WFPC 66-70, Proposal ID# 11972
11710 - At 067/02:44:25, REAcq (1,2,2) failed due to
QF1STOPF flag on
FGS-1. The REAcq was scheduled from 067/02:41:24 - 02:48:43.
Observations affected: WFPC 71 - 74, Proposal ID# 11972
COMPLETED OPS REQUEST: (None)
COMPLETED OPS NOTES: (None)
SCHEDULED
SUCCESSFUL
FGS GSAcq
15
15
FGS
REAcq
25
23
OBAD with Maneuver
80
80
SIGNIFICANT EVENTS: (None)