Daily Report #4625

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT***** # 4625

PERIOD COVERED: 5am June 04 - 5am June 05, 2008 (DOY
156/0900z-157/0900z)

OBSERVATIONS SCHEDULED

ACS/SBC 11230

HST FUV Observations of Brightest Cluster Galaxies: The Role of Star
Formation in Cooling Flows and BCG Evolution

The intracluster medium (ICM) now appears to be a very dynamic place
where heating and cooling processes vie for dominance and an uneasy
equilibrium is maintained. Since these same processes may operate
during the process of galaxy formation, the centers of clusters of
galaxies provide low redshift laboratories for studying the critical
processes involved in galaxy formation and black hole growth. At the
present time, the main questions are (1) How much gas is cooling out
of the ICM? (2) How much star formation is ongoing? (3) What is the
impact of the gas and star formation on the central BCG? In order to
measure the current star formation in BCGs we have undertaken a
program of Spitzer IRAC and MIPS observations. We are in process of
obtaining observations of a sample of Brightest Cluster Galaxies in 70
clusters selected from the ROSAT all sky survey. In about 25% of the
sources observed so far, we detect a mid-IR excess which we attribute
to dust heated by star formation. We propose to obtain ACS/SBC
observations of the Lyman Alpha emission line and the adjacent FUV
continuum in 7 BCGs which are in cooling core clusters of galaxies and
have a large mid-IR excess. We also propose WFPC2 F606W observations
of the two clusters without high resolution imaging to allow us to
image the dust on the same scale as the Far UV continuum. The FUV will
allow us to confirm the presence of ongoing star formation in these
BCGs and will allow us to rule out an AGN as the dominant contributor
to the mid-IR. The morphology and spatial extent of the young stars
and the heated dust and CO will constrain the spatial scale over which
star formation occurs and thus where the cooling gas is deposited. The
combination of our FUV and IR observations will allow us to estimate
the star formation rates which must balance the rate at which cold gas
is deposited in the BCG. Our proposed FUV observations will produce
unique information about the cooling gas, the true mass accretion
rates, and the star formation rates in BCGs and its effect on the
galaxy.

NIC1/NIC2/NIC3 8794

NICMOS Post-SAA Calibration - CR Persistence Part 5

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 DARKs. 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 images. Each observation will need its
own CRMAP, as different SAA passages leave different imprints on the
NICMOS detectors.

NIC2 11123

A NICMOS Survey for Proplyds in the RCW 38 Massive Embedded Cluster

We propose a search for line emission from photoevaporating
protoplanetary disks in the Massive Embedded Cluster RCW 38. These
disks would be analogous to the "proplyds" discovered in the Orion
Nebula: disks around young low mass stars which are being photoionized
by a nearby O star. We will search for these disks in RCW 38 using
narrowband imaging in the lines of Paschen alpha and molecular
hydrogen (1-0) S(1) with NICMOS. The RCW 38 region is an excellent
target for determining whether proplyds are observable in large
numbers outside of Orion. It is a young embedded cluster hosting a few
hundred low mass young stars with a large percentage showing infrared
excess indicating the presence of disks. About 100 of these stars are
found within 0.1 pc of the central O5 star, and the cluster is located
within a cleared cavity 0.2 pc in size, embedded within a molecular
cloud, exposing the cluster members directly to the UV radiation from
the O star. Unlike Orion, but like many other young clusters, RCW 38
is not seen in visible light, and infrared imaging is needed. The best
line in the infrared for revealing proplyds is the Paschen alpha line,
which is not detectable from the ground. Only HST is able to perform
these observations. From these observations we will estimate the
lifetime of the evaporating disks, and ascertain whether these disks
will survive long enough to form planets.

NIC2 11148

High Contrast Imaging of Dusty White Dwarfs

For the past 18 years, only one white dwarf with a circumstellar dust
disk was known to exist. In the last two years, six new disks have
been discovered. Since all material inwards of a few AU should be
scoured clean during post main sequence evolution, the primary
explanation is the presence of a planetary system that is perturbing
relic planetesimals into the tidal disruption radius of the white
dwarf. Dusty disks around white dwarfs should be markers for planets
and we propose to use high contrast imaging to search for faint
companions down to 6 M_$J$ that may be feeding the disks. White dwarfs
are uniquely suited for planet searches, where the planet/white dwarf
contrast is less than for main sequence stars.

NIC2 11157

NICMOS Imaging Survey of Dusty Debris Around Nearby Stars Across the
Stellar Mass Spectrum

Association of planetary systems with dusty debris disks is now quite
secure, and advances in our understanding of planet formation and
evolution can be achieved by the identification and characterization
of an ensemble of debris disks orbiting a range of central stars with
different masses and ages. Imaging debris disks in starlight scattered
by dust grains remains technically challenging so that only about a
dozen systems have thus far been imaged. A further advance in this
field needs an increased number of imaged debris disks. However, the
technical challenge of such observations, even with the superb
combination of HST and NICMOS, requires the best targets. Recent HST
imaging investigations of debris disks were sample-limited not limited
by the technology used. We performed a search for debris disks from a
IRAS/Hipparcos cross correlation which involved an exhaustive
background contamination check to weed out false excess stars. Out of
~140 identified debris disks, we selected 22 best targets in terms of
dust optical depth and disk angular size. Our target sample represents
the best currently available target set in terms of both disk
brightness and resolvability. For example, our targets have higher
dust optical depth, in general, than newly identified Spitzer disks.
Also, our targets cover a wider range of central star ages and masses
than previous debris disk surveys. This will help us to investigate
planetary system formation and evolution across the stellar mass
spectrum. The technical feasibility of this program in two-gyro mode
guiding has been proven with on-orbit calibration and science
observations during HST cycles 13, 14, and 15.

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.

WFPC2 11201

Systemic and Internal motions of the Magellanic Clouds: Third Epoch
Images

In Cycles 11 and 13 we obtained two epochs of ACS/HRC data for fields
in the Magellanic Clouds centered on background quasars. We used these
data to determine the proper motions of the LMC and SMC to better than
5% and 15% respectively. These are by far the best determinations of
the proper motions of these two galaxies. The results have a number of
unexpected implications for the Milky Way-LMC-SMC system. The implied
three-dimensional velocities are larger than previously believed, and
are not much less than the escape velocity in a standard 10^12 solar
mass Milky Way dark halo. Orbit calculations suggest the Clouds may
not be bound to the Milky Way or may just be on their first passage,
both of which would be unexpected in view of traditional
interpretations of the Magellanic Stream. Alternatively, the Milky Way
dark halo may be a factor of two more massive than previously
believed, which would be surprising in view of other observational
constraints. Also, the relative velocity between the LMC and SMC is
larger than expected, leaving open the possibility that the Clouds may
not be bound to each other. To further verify and refine our results
we now request an epoch of WFPC2/PC data for the fields centered on 40
quasars that have at least one epoch of ACS imaging. We request
execution in snapshot mode, as in our previous programs, to ensure the
most efficient use of HST resources. A third epoch of data of these
fields will provide crucial information to verify that there are no
residual systematic effects in our previous measurements. More
importantly, it will increase the time baseline from 2 to 5 yrs and
will increase the number of fields with at least two epochs of data.
This will reduce our uncertainties correspondingly, so that we can
better address whether the Clouds are indeed bound to each other and
to the Milky Way. It will also allow us to constrain the internal
motions of various populations within the Clouds, and will allow us to
determine a distance to the LMC using rotational parallax.

WFPC2 11227

The Orbital Period for an Ultraluminous X-ray Source in NGC1313

The ultraluminous X-ray sources {ULXs} are extragalactic point sources
with luminosities that exceed the Eddington luminosity for
conventional stellar-mass black holes by factors of 10 - 100. It has
been hotly debated whether the ULXs are just common stellar-mass black
hole sources with beamed emission or whether they are sub-Eddington
sources that are powered by the long-sought intermediate mass black
holes {IMBH}. To firmly decide this question, one must obtain
dynamical mass measurements through photometric and spectroscopic
monitoring of the secondaries of these system. The crucial first step
is to establish the orbital period of a ULX, and arguably the best way
to achieve this goal is by monitoring its ellipsoidal light curve. The
extreme ULX NGC1313 X-2 provides an outstanding target for an orbital
period determination because its relatively bright optical counterpart
{V = 23.5} showed a 15% variation between two HST observations
separated by three months. This level of variability is consistent
with that expected for a tidally distorted secondary star. Here we
propose a set of 20 imaging observations with HST/WFPC2 to define the
orbital period. This would be the first photometric measurement of the
orbital period of a ULX binary. Subsequently, we will propose to
obtain spectroscopic observations to obtain its radial velocity
amplitude and thereby a dynamical estimate of its mass.

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*************** 12***************** 12
FGS REacq*************** 02***************** 02
OBAD with Maneuver* **** 28***************** 28

SIGNIFICANT EVENTS: (None)