HUBBLE SPACE TELESCOPE - Continuing to collect World Class
Science
DAILY REPORT #4673
PERIOD COVERED: 5am August 12 - 5am August 13, 2008 (DOY
225/0900z-226/0900z)
OBSERVATIONS SCHEDULED
ACS/SBC 11151
Evaluating the Role of Photoevaporation of Protoplanetary
Disk Dispersal
Emission produced by accretion onto the central star leads
to
photoevaporation, which may play a fundamental role in
disk dispersal.
Models of disk photoevaporation by the central star are
challenged by
two potential problems: the emission produced by accretion
will be
substantially weaker for low-mass stars, and
photoevaporation must
continue as accretion slows. Existing FUV spectra of CTTSs
are biased to
solar-mass stars with high accretion rates, and are
therefore
insufficient to address these problems. We propose use
HST/ACS SBC
PR130L to obtain FUV spectra of WTTSs and of CTTSs at low
masses and
mass accretion rates to provide crucial data to evaluate
photoevaporation models. We will estimate the FUV and EUV
luminosities
of low-mass CTTSs with small mass accretion rates, CTTSs
with transition
disks and slowed accretion, and of magnetically-active
WTTSs.
ACS/SBC WFPC2 11175
UV Imaging to Determine the Location of Residual Star
Formation in
Galaxies Recently Arrived on the Red Sequence
We have identified a sample of low-redshift {z = 0.04 -
0.10} galaxies
that are candidates for recent arrival on the red
sequence. They have
red optical colors indicative of old stellar populations,
but blue
UV-optical colors that could indicate the presence of a
small quantity
of continuing or very recent star formation. However,
their spectra lack
the emission lines that characterize star-forming
galaxies. We propose
to use ACS/SBC to obtain high-resolution imaging of the UV
flux in these
galaxies, in order to determine the spatial distribution
of the last
episode of star formation. WFPC2 imaging will provide B,
V, and I
photometry to measure the main stellar light distribution
of the galaxy
for comparison with the UV imaging, as well as to measure
color
gradients and the distribution of interstellar dust. This
detailed
morphological information will allow us to investigate the
hypothesis
that these galaxies have recently stopped forming stars
and to compare
the observed distribution of the last star formation with
predictions
for several different mechanisms that may quench star
formation in
galaxies.
NIC1/NIC2/NIC3 11330
NICMOS Cycle 16 Extended Dark
This takes a series of Darks in parallel to other
instruments.
NIC1/NIC2/NIC3 8795
NICMOS Post-SAA Calibration - CR Persistence Part 6
A new procedure proposed to alleviate the CR-persistence
problem of
NICMOS. Dark frames will be obtained immediately upon
exiting the SAA
contour 23, and every time a NICMOS exposure is scheduled
within 50
minutes of coming out of the SAA. The darks will be
obtained in parallel
in all three NICMOS Cameras. The POST-SAA darks will be
non-standard
reference files available to users with a USEAFTER
date/time mark. The
keyword 'USEAFTER=date/time' will also be added to the
header of each
POST-SAA DARK frame. The keyword must be populated with
the time, in
addition to the date, because HST crosses the SAA ~8 times
per day so
each POST-SAA DARK will need to have the appropriate time
specified, for
users to identify the ones they need. Both the raw and
processed images
will be archived as POST-SAA DARKSs. Generally we expect
that all NICMOS
science/calibration observations started within 50 minutes
of leaving an
SAA will need such maps to remove the CR persistence from
the science i
mages. Each observation will need its own CRMAP, as
different SAA
passages leave different imprints on the NICMOS detectors.
NIC2 11101
The Relevance of Mergers for Fueling AGNs: Answers from
QSO Host
Galaxies
The majority of QSOs are known to reside in centers of galaxies
that
look like ellipticals. Numerical simulations have shown
that remnants of
galaxy mergers often closely resemble elliptical galaxies.
However, it
is still strongly debated whether the majority of QSO host
galaxies are
indeed the result of relatively recent mergers or whether
they are
completely analogous to inactive ellipticals to which
nothing
interesting has happened recently. To address this
question, we recently
obtained deep HST ACS images for five QSO host galaxies
that were
classified morphologically as ellipticals {GO-10421}. This
pilot study
revealed striking signs of tidal interactions such as
ripples, tidal
tails, and warped disks that were not detected in previous
studies. Our
observations show that at least some "elliptical"
QSO host galaxies are
the products of relatively recent merger events rather
than old galaxies
formed at high redshift. However, the question remains
whether the host
galaxies of classical QSOs are truly distinct from
inactive ellipticals
and whether there is a connection between the merger
events we detect
and the current nuclear activity. We must therefore place
our results
into a larger statistical context. We are currently
conducting an HST
archival study of inactive elliptical galaxies {AR- 10941}
to form a
control sample. We now propose to obtain deep HST/WFPC2
images of 13
QSOs whose host galaxies are classified as normal
ellipticals. Comparing
the results for both samples will help us determine
whether classical
QSOs reside in normal elliptical galaxies or not. Our
recent pilot study
of five QSOs indicates that we can expect exciting results
and deep
insights into the host galaxy morphology also for this
larger sample of
QSOs. A statistically meaningful sample will help us
determine the true
fraction of QSO hosts that suffered strong tidal
interactions and thus,
whether a merger is indeed a requirement to trigger
nuclear activity in
the most luminous AGNs. In addition to our primary science
observations
with WFPC2, we will obtain NICMOS3 parallel observations
with the
overall goal to select and characterize galaxy populations
at high
redshifts. The imaging will be among the deepest NICMOS
images: These
NICMOS images are expected to go to a limit a little over
1 magnitude
brighter than HUDF-NICMOS data, but over 13 widely
separated fields,
with a total area about 1.5 times larger than HUDF-
NICMOS. This
separation means that the survey will tend to average out
effects of
cosmic variance. The NICMOS3 images will have sufficient
resolution for
an initial characterization of galaxy morphologies, which
is currently
one of the most active and promising areas in approaching
the problem of
the formation of the first massive galaxies. The depth and
area coverage
of our proposed NICMOS observations will also allow a
careful study of
the mass function of galaxies at these redshifts. This
provides a large
and unbiased sample, selected in terms of stellar mass and
unaffected by
cosmic variance, to study the on-going star formation
activity as a
function of mass {i.e. integrated star formation} at this
very important
epoch.
NIC2 11164
Molecular Hydrogen Disks Around T Tauri Stars
We propose to measure the properties of planetary
system-sized disks
around Sun- like, pre-main sequence stars by imaging the
inner parts of
these disks for the first time in gaseous emission from
their most
dominant constituent, molecular hydrogen gas. Specifically, we will use
the F212N filter and NICMOS to determine the spatial
distribution of
ro-vibrational H2 emission from protoplanetary disks
around selected
classical and weak-lined T Tauri stars. The target stars
are among those
detected by members of this team through high resolution,
ground-based
infrared spectroscopy. The spectra reveal H2 emission at
the rest
velocities of the stars and at positions spatially
coincident with the
stars at the spatial resolution of the spectroscopic data.
This imaging
experiment, which is impossible to do using ground- based
facilities, is
possible using the NICMOS camera aboard the HST because
the point spread
function of this system is extremely stable and can be
measured to a
very high accuracy. This experiment is an important test
of the
interpretation that the 2.122 micron H2 line emission seen
toward T
Tauri stars is produced at distances of 10 to 30 AU from
the stars, the
region in which giant planets are expected to form around
these stars.
These observations will contribute toward developing a
better
understanding of the process, likelihood, and timescale
for the
formation of planets around Sun-like stars.
NIC2 11548
NICMOS Imaging of Protostars in the Orion A Cloud: The
Role of
Environment in Star Formation
We propose NICMOS observations of a sample of 252
protostars identified
in the Orion A cloud with the Spitzer Space Telescope.
These
observations will image the scattered light escaping the
protostellar
envelopes, providing information on the shapes of outflow
cavities, the
inclinations of the protostars, and the overall
morphologies of the
envelopes. In addition, we ask for Spitzer time to obtain
55-95 micron
spectra of 75 of the protostars. Combining these new data
with existing
3.6 to 70 micron photometry and forthcoming 5-40 micron
spectra measured
with the Spitzer Space Telescope, we will determine the
physical
properties of the protostars such as envelope density,
luminosity,
infall rate, and outflow cavity opening angle. By
examining how these
properties vary with stellar density (i.e. clusters vs
groups vs
isolation) and the properties of the surrounding molecular
cloud; we can
directly measure how the surrounding environment
influences protostellar
evolution, and consequently, the formation of stars and
planetary
systems. Ultimately, this data will guide the development
of a theory of
protostellar evolution.
WFPC2 11203
A Search for Circumstellar Disks and Planetary-Mass
Companions around
Brown Dwarfs in Taurus
During a 1-orbit program in Cycle 14, we used WFPC2 to
obtain the first
direct image of a circumstellar disk around a brown dwarf.
These data
have provided fundamental new constraints on the formation
process of
brown dwarfs and the properties of their disks. To search
for additional
direct detections of disks around brown dwarfs and to
search for
planetary-mass companions to these objects, we propose a
WFPC2 survey of
32 brown dwarfs in the Taurus star-forming region.
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
09
09
FGS REacq
06
06
OBAD with Maneuver
30
30
SIGNIFICANT EVENTS: (None)