HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT       #4814

PERIOD COVERED: 5am March 18 - 5am March 19, 2009 (DOY

                           077/0900z-078/0900z)

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 11980

Deep FUV Imaging of Cooling Flow Clusters

We propose to take deep ACS FUV images of a carefully selected sample of

19 bright central galaxies in nearby galaxy clusters. This program is

the last critical element of a comprehensive investigation of the impact

of stellar and AGN feedback on the local galaxy cluster environment. The

HST images will complement new, high-resolution, Halpha images obtained

with the recently commissioned Maryland-Magellan Tunable Filter (MMTF)

on the Baade 6.5m telescope, archival Chandra, VLA, and GALEX data, and

on-going H2/NIR observations. The MMTF data have revealed unsuspected

filamentary complexes in several systems. The GALEX data often show

hints of extended NUV and FUV emission on a similar scale, but their

poor spatial resolution prevents meaningful comparison with the MMTF

data. The HST data will provide this much needed gain in resolution. The

combined radio-H2-Halpha-FUV-X-ray dataset will allow us to derive with

unprecedented precision the role of the AGN, hot stars, shocks, and

relativistic particles on the excitation and thermodynamics of the

multi-phase intracluster and interstellar media in these systems. This

is an important question since the formation and evolution of most

cluster galaxies have likely been affected by these processes.

FGS 11789

An Astrometric Calibration of Population II Distance Indicators

In 2002 HST produced a highly precise parallax for RR Lyrae. That

measurement resulted in an absolute magnitude, M(V)= 0.61+/-0.11, a

useful result, judged by the over ten refereed citations each year

since. It is, however, unsatisfactory to have the direct,

parallax-based, distance scale of Population II variables based on a

single star. We propose, therefore, to obtain the parallaxes of four

additional RR Lyrae stars and two Population II Cepheids, or W Vir

stars. The Population II Cepheids lie with the RR Lyrae stars on a

common K-band Period-Luminosity relation. Using these parallaxes to

inform that relationship, we anticipate a zero-point error of 0.04

magnitude. This result should greatly strengthen confidence in the

Population II distance scale and increase our understanding of RR Lyrae

star and Pop II Cepheid astrophysics.

WFPC2 11975

UV Light from Old Stellar Populations: a Census of UV Sources in

Galactic Globular Clusters

In spite of the fact that HST has been the only operative

high-resolution eye in the UV-window over the last 18 years, no

homogeneous UV survey of Galactic globular clusters (GGCs) has been

performed to date. In order to fill this gap in the stellar population

studies, we propose a program that exploits the unique capability of the

WFPC2 and the SBC in the far-/mid- UV for securing deep UV imaging of 46

GGCs. The proposed observations will allow to study with unprecedented

accuracy the hottest GGC stars, comprising the extreme horizontal branch

(HB) stars and their progeny (the so-called AGB-manque', and Post-early

AGB stars), and "exotic stellar populations" like the blue straggler

stars and the interacting binaries. The targets have been selected to

properly sample the GGC metallicity/structural parameter space, thus to

unveil any possible correlation between the properties of the hot

stellar populations and the cluster characteristics. In addition, most

of the targets have extended HB "blue tails", that can be properly

studied only by means of deep UV observations, especially in the far-UV

filters like the F160BW, that is not foreseen on the WFC3. This data

base is complemented with GALEX observations in the cluster outermost

regions, thus allowing to investigate any possible trend of the

UV-bright stellar types over the entire radial extension of the

clusters. Although the hottest GGC stars are just a small class of

"special" objects, their study has a broad relevance in the context of

structure formation and chemical evolution in the early Universe,

bringing precious information on the basic star formation processes and

the origin of blue light from galaxies. Indeed, the proposed

observations will provide the community with an unprecedented data set

suitable for addressing a number of still open astrophysical questions,

ranging from the main drivers of the HB morphology and the mass loss

processes, to the origin of the UV upturn in elliptical galaxies, the

dating of distant systems from integrated light, and the complex

interplay between stellar evolution and dynamics in dense stellar

aggregates. In the spirit of constructing a community resource, we

entirely waive the proprietary period for these observations.

WFPC2 11988

Searching for Intermediate Mass Black Holes in Globular Clusters via

Proper Motions

The unambiguous detection of an intermediate mas black hole (IMBH) in a

globular star cluster would be a major achievement for the Hubble Space

Telescope. It is critical to know whether or not IMBHs exist in the

centers of clusters in order to understand the dynamical evolution of

dense stellar systems. Also, n IMBH detection would prove the existence

of BHs in an entirely new mass range. Observationally, the search has

been hampered by the low number of stars with known velocities in the

central few arcseconds. This limits measurements of the stellar velocity

dispersion in the region where the gravitational influence of any IMBH

would be felt. Existing IMBH claims i the literature have all been

called into question, and have all been based on line-of-sight

velocities from spectroscopy. In cycle 13, we obtained ACS/HRC

observations for 5 nearby Galactic globular clusters for a new proper

motion study. Here, we request WFPC2/PC observations of these clusters,

all of which are observable in Feb-May 2009. This 4 year baseline will

allow us to measure the proper motions of stars into the very center of

each cluster, and either detect or place firm constraints on the

presence of an IMBH. In addition, we will determine whether or not the

clusters rotate or show any anisotropy in their motions. Our small (<75

orbit) program meets the criteria of addressing high impact science

(IMBH detection) using innovative methods (proper motions).

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               08                  08               

FGS REAcq               05                  05               

OBAD with Maneuver 24                  24              

SIGNIFICANT EVENTS: (None)