HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT       #4817

PERIOD COVERED: 5am March 23 - 5am March 24, 2009 (DOY

                           082/0900z-083/0900z)

OBSERVATIONS SCHEDULED

WFPC2 11113

Binaries in the Kuiper Belt: Probes of Solar System Formation and

Evolution

The discovery of binaries in the Kuiper Belt and related small body

populations is powering a revolutionary step forward in the study of

this remote region. Three quarters of the known binaries in the Kuiper

Belt have been discovered with HST, most by our snapshot surveys. The

statistics derived from this work are beginning to yield surprising and

unexpected results. We have found a strong concentration of binaries

among low-inclination Classicals, a possible size cutoff to binaries

among the Centaurs, an apparent preference for nearly equal mass

binaries, and a strong increase in the number of binaries at small

separations. We propose to continue this successful program in Cycle 16;

we expect to discover at least 13 new binary systems, targeted to

subgroups where these discoveries can have the greatest impact.

WFPC2 11302

WFPC2 CYCLE 16 Standard Darks - Part III

This dark calibration program obtains dark frames every week in order to

provide data for the ongoing calibration of the CCD dark current rate,

and to monitor and characterize the evolution of hot pixels. Over an

extended period these data will also provide a monitor of radiation

damage to the CCDs.

WFPC2 11793

WFPC2 Cycle 16 Internal Monitor

This calibration proposal is the Cycle 15 routine internal monitor for

WFPC2, to be run weekly to monitor the health of the cameras. A variety

of internal exposures are obtained in order to provide a monitor of the

integrity of the CCD camera electronics in both bays (both gain 7 and

gain 15 -- to test stability of gains and bias levels), a test for

quantum efficiency in the CCDs, and a monitor for possible buildup of

contaminants on the CCD windows. These also provide raw data for

generating annual super-bias reference files for the calibration

pipeline.

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 11986

Completing HST's Local Volume Legacy

Nearby galaxies offer one of the few laboratories within which stellar

populations can be tied to multi-wavelength observations. They are thus

essential for calibrating and interpreting key astrophysical

observables, such as broad-band luminosities, durations and energy input

from starbursts, and timescales of UV, H-alpha, and FIR emission. The

study of stellar populations in nearby galaxies requires high-resolution

observations with HST, but HST's legacy for this limited set of galaxies

remains incomplete.

As a first attempt to establish this legacy, The ACS Nearby Galaxy

Survey Treasury (ANGST) began observations in late 2006. ANGST was

designed to carry out a uniform multi-color survey of a volume-limited

sample of ~70 nearby galaxies that could be used for systematic studies

of resolved stellar populations. The resulting data provide nuanced

constraints on the processes which govern star formation and galaxy

evolution, for a well-defined population of galaxies. All photometry for

the survey has been publicly released.

However, the failure of ACS 4.5 months after ANGST began taking data led

to a drastic reduction in the planned survey. The loss is two-fold.

First, the goals of completeness and uniformity were greatly

compromised, impacting global comparison studies. Second, the variety of

observed star formation histories was reduced. Given that we have never

found two galaxies with identical star formation histories, and fully

sampling the population allows us to catch those few systems whose star

formation rates and metallicities place the strongest constraints on key

astrophysical processes.

Here we propose WFPC2 observations of all remaining galaxies within the

Local Volume (D<3.5Mpc) for which current HST observations are

insufficient for meaningful stellar population studies. We will use

these observations for research on the star formation histories of

individual galaxies and the Local Volume, detailed calibrations of star

formation rate indicators, and the durations of starbursts. We will also

make them publicly available through the ANGST archive to support future

research. The proposed observations will finally complete a lasting

legacy of HST

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               05                 05                         

FGS REAcq               08                 08                          

OBAD with Maneuver 26                 26              

SIGNIFICANT EVENTS: (None)