HUBBLE
SPACE TELESCOPE - Continuing to Collect World Class Science
DAILY
REPORT #5084
PERIOD
COVERED: 5am April 27 - 5am April 28, 2010 (DOY 117/09:00z-118/09:00z)
OBSERVATIONS
SCHEDULED
ACS/WFC/WFC3/UV
11578
The
Extremely Metal-Poor BCD Galaxy DDO 68: a Young Galaxy in the Local
Universe
?
A
long standing question in astrophysics is the existence of young
galaxies,
in which stars are now forming for the first time, in the
nearby
(i.e., present-day) universe. Such galaxies would be the local
analogs
of primordial galaxies observed at high redshift. The most
promising
candidates have long been the most metal-poor systems,
including
dwarf irregulars (dIrrs) and blue compact dwarfs (BCDs).
However,
in many dIrrs and BCDs studied with HST an old (1 Gyr)
underlying
stellar population, as traced by red giant branch (RGB)
stars,
has been unambiguously detected. Even in I Zw 18, which is the
most-metal
poor prototype of the class and long the most controversial
case,
our group has recently succeeded in detecting an RGB. Nonetheless,
there
remains the possibility that the star formation histories of
BCDs/dIrrs
vary from galaxy to galaxy, and that truly young galaxies do
exist
in the local universe. A new test of these issues has only
recently
become possible with the identification of DDO 68 as an
extremely
metal-poor galaxy with an oxygen abundance equal to that of I
Zw
18 (12+(O/H)=7.21). This galaxy is about a factor of 2-3 closer than
I
Zw 18, which yields the opportunity to avoid the many ambiguities that
have
plagued studies of I Zw 18. Also, DDO 68 resides in a void, making
it
more likely that star formation has been suppressed for a very long
time.
We will observe DDO 68 with ACS/WFC in F606W and F814W, plus F658N
(Halpha)
to correct the broad F606W for gas contamination. We will use
WFC3
in parallel with the same filters to study radial population
gradients.
Deep color-magnitude diagrams (CMDs) reaching the depth of
one
magnitude below the predicted RGB tip will be constructed and
interpreted
based on synthetic CMD fitting. These data will determine
unambiguously
whether DDO 68 has an underlying old (RGB) stellar
population
or is forming stars for the first time. Finding just a single
nearby
``young'' galaxy would have profound cosmological implications.
COS/NUV/FUV/WFC3/UVIS/IR
11533
COS-GTO:
Accretion Flows and Winds of Pre-Main Sequence Stars
COS
will obtain spectra of T Tauri stars to study accretion flows and
wind
absorption features in ultraviolet emission lines. Observations of
several
T Tauri stars with different inclination angles with respect to
the
line of sight will determine the temperature distributions, flow
velocities,
and column densities of both inflows and outflows for these
stars.
STIS/CC
11845
CCD
Dark Monitor Part 2
Monitor
the darks for the STIS CCD.
STIS/CC
11847
CCD
Bias Monitor-Part 2
Monitor
the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at gain=1,
and
1x1 at gain = 4, to build up high-S/N superbiases and track the
evolution
of hot columns.
STIS/CCD
11852
STIS
CCD Spectroscopic Flats C17
The
purpose of this proposal is to obtain pixel-to-pixel lamp flat
fields
for the STIS CCD in spectroscopic mode.
STIS/CCD/FGS
11848
CCD
Read Noise Monitor
This
proposal measures the read noise of all the amplifiers (A, B, C, D)
on
the STIS CCD using pairs of bias frames. Full-frame and binned
observations
are made in both Gain 1 and Gain 4, with binning factors of
1x1,
1x2, 2x1, and 2x2. All exposures are internals. Pairs of visits are
scheduled
monthly for the first four months and then bi-monthly after
that.
WFC3/ACS/IR
11597
Spectroscopy
of IR-Selected Galaxy Clusters at 1 < z < 1.5
We
propose to obtain WFC3 G141 and G102 slitless spectroscopy of galaxy
clusters
at 1 < z < 1.5 that were selected from the IRAC survey of the
Bootes
NDWFS field. Our IRAC survey contains the largest sample of
spectroscopically
confirmed clusters at z > 1. The WFC3 grism data will
measure
H-alpha to determine SFR, and fit models to the low resolution
continua
to determine stellar population histories for the brighter
cluster
members, and redshifts for the red galaxies too faint for
ground-based
optical spectroscopy.
WFC3/IR
11936
IR
Grism Flux Calibration
This
program will determine image displacement, spectral trace and flux
calibration
for the IR G102 and G141 grisms as a function of spatial
position
within the field of view. The HST flux standard GD71 will be
observed
in a 9-point pattern in the IR field of view, which will
provide
the necessary image displacement, spectral trace, and throughput
measurements.
WFC3/IR/S/C
11929
IR
Dark Current Monitor
Analyses
of ground test data showed that dark current signals are more
reliably
removed from science data using darks taken with the same
exposure
sequences as the science data, than with a single dark current
image
scaled by desired exposure time. Therefore, dark current images
must
be collected using all sample sequences that will be used in
science
observations. These observations will be used to monitor changes
in
the dark current of the WFC3-IR channel on a day-to-day basis, and to
build
calibration dark current ramps for each of the sample sequences to
be
used by Gos in Cycle 17. For each sample sequence/array size
combination,
a median ramp will be created and delivered to the
calibration
database system (CDBS).
WFC3/UV/ACS/WFC
11636
First
Resolved Imaging of Escaping Lyman Continuum
The
emission from star-forming galaxies appears to be responsible for
reionization
of the universe at z > 6. However, the models that attempt
to
describe the detailed impact of high-redshift galaxies on the
surrounding
inter-galactic medium (IGM) are strongly dependent upon
several
uncertain parameters. Perhaps the most uncertain is the fraction
of
HI-ionizing photons produced by young stars that escape into the IGM.
Most
attempts to measure this "escape fraction" have produced null
results.
Recently, a small subset of z~3 Lyman Break Galaxies (LBGs) has
been
found exhibiting large escape fractions. It remains unclear
however,
what differentiates them from other LBGs. Several models
attempt
to explain how such a large fraction of ionizing continuum can
escape
through the HI and dust in the ISM (eg. "chimneys" created by SNe
winds,
globular cluster formation, etc.), each producing unique
signatures
which can be observed with resolved imaging of the escaping
Lyman
continuum. To date, there are only six LBGs with individual
detections
of escaping Lyman continuum at any redshift. We propose a
single
deep, high resolution WFC3/UVIS image of the ionizing continuum
(F336W)
and the rest-frame UV/optical (F606W/F814W/F160W) of five of
these
six LBGs with large escape fractions. These LBGs have a high
surface
density and large escape fractions, and lie at the optimal
redshift
for Lyman continuum imaging with UVIS filters, making our
sample
especially suitable for follow-up. With these data we will
discern
the mechanisms responsible for producing large escape fractions,
and
therefore gain insight into the process of reionization.
WFC3/UVIS
11594
A
WFC3 Grism Survey for Lyman Limit Absorption at z=2
We
propose to conduct a spectroscopic survey of Lyman limit absorbers at
redshifts
1.8 < z < 2.5, using WFC3 and the G280 grism. This proposal
intends
to complete an approved Cycle 15 SNAP program (10878), which was
cut
short due to the ACS failure. We have selected 64 quasars at 2.3 < z
<
2.6 from the Sloan Digital Sky Survey Spectroscopic Quasar Sample, for
which
no BAL signature is found at the QSO redshift and no strong metal
absorption
lines are present at z > 2.3 along the lines of sight. The
survey
has three main observational goals. First, we will determine the
redshift
frequency dn/dz of the LLS over the column density range 16.0 <
log(NHI)
< 20.3 cm^-2. Second, we will measure the column density
frequency
distribution f(N) for the partial Lyman limit systems (PLLS)
over
the column density range 16.0 < log(NHI) < 17.5 cm^-2. Third, we
will
identify those sightlines which could provide a measurement of the
primordial
D/H ratio. By carrying out this survey, we can also help
place
meaningful constraints on two key quantities of cosmological
relevance.
First, we will estimate the amount of metals in the LLS using
the
f(N), and ground based observations of metal line transitions.
Second,
by determining f(N) of the PLLS, we can constrain the amplitude
of
the ionizing UV background at z~2 to a greater precision. This survey
is
ideal for a snapshot observing program, because the on-object
integration
times are all well below 30 minutes, and follow-up
observations
from the ground require minimal telescope time due to the
QSO
sample being bright.
WFC3/UVIS
11905
WFC3
UVIS CCD Daily Monitor
The
behavior of the WFC3 UVIS CCD will be monitored daily with a set of
full-frame,
four-amp bias and dark frames. A smaller set of 2Kx4K
subarray
biases are acquired at less frequent intervals throughout the
cycle
to support subarray science observations. The internals from this
proposal,
along with those from the anneal procedure (Proposal 11909),
will
be used to generate the necessary superbias and superdark reference
files
for the calibration pipeline (CDBS).
WFC3/UVI
11911
UVIS
L-Flats and Geometric Distortion
Multiple
pointing observations of the globular cluster Omega Centauri (NGC 5139) will be
used to
measure
the filter-dependent low frequency flat field (L-flat) corrections and
stability for a key
set
of 10 broadband filters used by GO programs. The selected filters are F225W,
F275W, F336W,
F390W,
F438W, F555W, F606W, F775W, F814W and F850LP. By measuring relative changes in
brightness of
a
star over different portions of the detector, we will determine local
variations in the UVIS
detector
response. The broad wavelength range covered by these observations will allow
us to derive
the
L-flat correction for the remaining wide, medium and narrow-band UVIS filters.
The same data
will
also be used to determin and correct the geometric distotrion that affects UVIS
data. The broad
wavelength
range covered by these observations will allow us to measure the geometric
distortion
dependence
with wavelength and filters and to provide the most appropriate correction over
the
entire
wavelength range provided by UVIS.
ACS/WFC
11995
CCD
Daily Monitor (Part 2)
This
program comprises basic tests for measuring the read noise and dark current of
the ACS WFC and
for
tracking the growth of hot pixels. The recorded frames are used to create bias
and dark
reference
images for science data reduction and calibration. This program will be
executed four days
per
week (Mon, Wed, Fri, Sun) for the duration of Cycle 17. To facilitate
scheduling, this program
is
split into three proposals. This proposal covers 320 orbits (20 weeks) from 1
February 2010 to 20
June
2010.
FLIGHT
OPERATIONS SUMMARY:
Significant
Spacecraft Anomalies: (The following are preliminary reports
of
potential non-nominal performance that will be investigated.)
HSTARS:
12255
- Following successful GSAcq(2,3,3), a Loss of Lock occurred while
guiding with FGS-2, and FGS-3 at 188/04:27:02z. Subsequent
REAcqs(2,3,3)
were successful.
Observations possibly affected. WFC3 47 Proposal ID#11911, ACS
#85,
Proposal ID#11995.
COMPLETED
OPS REQUEST: (None)
COMPLETED
OPS NOTES: (None)
SCHEDULED SUCCESSFUL FAILURE TIMES
FGS
GSAcq
06
06
FGS
REAcq
10
10
OBAD
with Maneuver 03 03
LOSS
of LOCK
118/04:29:57z
SIGNIFICANT
EVENTS: (None)