HUBBLE SPACE TELESCOPE - Continuing to collect World Class
Science
DAILY REPORT #4784
PERIOD COVERED: 5am February 3 - 5am February 4, 2009 (DOY
034/1000z-035/1000z)
OBSERVATIONS SCHEDULED
ACS/SBC 11579
The Difference Between Neutral- and Ionized-Gas Metal
Abundances in
Local Star-Forming Galaxies with COS
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 COS on HST now
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 11942
Increasing the Accuracy of HST Astrometry with FGS1R
We propose to observe six exoplanetary system host stars
and two
planetary nebulae central stars with FGS1r. All objects
have been
previously observed under proposals GO-09233, -09969,
-10989, and
-11210. These observations will significantly extend the
time baseline,
permitting improvements in the determination of proper
motion. This
systematic motion must be removed to get at the
perturbation of
interest, either due to exoplanetary companions or the
orbital motion of
the Earth (parallax). In most cases the perturbation
orbits will also
improve. We improve either companion mass or PN parallax.
For one
target, GJ 876, theoretical dynamical modelers have
proposed an
inclination closer to 50 degrees, while FGS3 measurements
indicated an
inclination closer to 84 degrees. These new data, once
combined with our
older FGS3 data, will permit an independent remeasurement
of the
inclination of the outermost companion, and a
re-evaluation of widely
used dynamical algorithms.
NIC3 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 11787
Dynamical Masses and Radii of Four White Dwarf Stars
This proposal uses the FGS1r in TRANS mode to resolve a
pair of double
degenerate binary systems {WD1639+153 and WD 1818+26} in
order to
determine their orbital elements. In addition, the
binaries and several
nearby field stars are observed by FGS1r in POS mode to
establish the
local inertial reference frame of each binary, as well as
its parallax
and proper motion. This will allow for a direct
measurement of the
distance, which yields the instrinsic luminosity, and when
combined with
the spectroscopic estimates of the T_eff, the radius of
each of the four
WD stars. When combined with the orbital elements, this
leads to a
dynamical mass measurement for each WD, and a four
calibration points of
the WD mass-radius relation.;
WFPC2 11797
Supplemental WFPC2 CYCLE 16 Intflat Linearity Check and
Filter Rotation
Anomaly Monitor
Supplemental observations to 11029, to cover period from
Aug 08 to SM4.
Intflat observations will be taken to provide a linearity
check: the
linearity test consists of a series of intflats in F555W,
in each gain
and each shutter. A combination of intflats, visflats, and
earthflats
will be used to check the repeatability of filter wheel
motions.
(Intflat sequences tied to decons, visits 1-18 in prop
10363, have been
moved to the cycle 15 decon proposal 11022 for easier
scheduling.)
Note: long-exposure WFPC2 intflats must be scheduled
during ACS anneals
to prevent stray light from the WFPC2 lamps from
contaminating long ACS
external exposures.
Note: These are supplemental observations to cover June to
SM4 (Oct 8
'08) + 6 months.
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:
11662 – REacq(2,1,2) Failed due to Stop Flag @
034/18:53:47z
Observations affected: ACS 7 - 8 Proposal ID#11236
COMPLETED OPS REQUEST: (None)
COMPLETED OPS NOTES: (None)
SCHEDULED
SUCCESSFUL
FGS
GSacq
10
10
FGS
REacq
03
02
OBAD with Maneuver
20
20
SIGNIFICANT EVENTS: (None)