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)