HUBBLE SPACE TELESCOPE - Continuing to collect World Class
Science
DAILY REPORT #4781
PERIOD COVERED: 5am January 29 - 5am January 30, 2009 (DOY
029/1000z-030/1000z)
OBSERVATIONS SCHEDULED
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.
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 11789
An Astrometric Calibration of Population II Distance
Indicators
In 2002 HST produced a highly precise parallax for RR
Lyrae. That
measurement resulted in an absolute magnitude, M(V)=
0.61+/-0.11, a
useful result, judged by the over ten refereed citations
each year
since. It is, however, unsatisfactory to have the direct,
parallax-based, distance scale of Population II variables
based on a
single star. We propose, therefore, to obtain the
parallaxes of four
additional RR Lyrae stars and two Population II Cepheids,
or
stars. The Population II Cepheids lie with the RR Lyrae
stars on a
common K-band Period-Luminosity relation. Using these
parallaxes to
inform that relationship, we anticipate a zero-point error
of 0.04
magnitude. This result should greatly strengthen
confidence in the
Population II distance scale and increase our
understanding of RR Lyrae
star and Pop II Cepheid astrophysics.
ACS/SBC 11236
Did Rare, Large Escape-Fraction Galaxies Reionize the
Universe?
Lyman continuum photons produced in massive starbursts may
have played a
dominant role in the reionization of the Universe. Starbursts
are
important contributors to the ionizing metagalactic
background at lower
redshifts as well. However, their contribution to the
background depends
upon the fraction of ionizing radiation that escapes from
the intrinsic
opacity of galaxies below the Lyman limit. Current surveys
suggest that
the escape fraction is close to zero in most galaxies,
even among young
starbursts, but is large in 15-25% of them. Non-uniform
escape fractions
are expected as a result of violent events creating clear
paths in small
parts of galaxies. The number of galaxies observed with
high escape
fraction will result from the combination of the intrinsic
number with
clear lines of sight and their orientation with respect to
the observer.
We propose to measure the fraction of escaping Lyman
continuum radiation
in a large sample (47) of z~0.7 starbursts in the COSMOS
field. These
compact UV-luminous galaxies are good analogs to high
redshift LBGs.
Using the SBC/PR130L we can quickly (1-4 orbits) detect
relative escape
fractions (f_LC/f_1500) of 25% or more. This will be the
first
measurement of the escape fraction in sources between z=1
and the local
universe. We expect ~10 detections. Stacking will set
limits of <4% on
the relative escape fraction in the rest. We will correlate
the LC
detections with the properties of the galaxies. By
targeting z~0.7 in
COSMOS, we will have tremendous ancillary information on
those sources.
A non-detection in all sources would be significant (99%
confidence).
This would imply that QSOs provide the overwhelming
majority of ionizing
radiation at z<1, requiring substantial evolution in
the processes
within Lyman break galaxies which allow large escape
fractions at high
redshift.
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.
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
08
08
FGS
REacq
03
03
OBAD with Maneuver
23
23
SIGNIFICANT EVENTS: (None)