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

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)