HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT      #4838

PERIOD COVERED: 5am April 21 - 5am April 22, 2009 (DOY

                           111/0900z-112/0900z)

OBSERVATIONS SCHEDULED

WFPC2 11974

High-resolution Imaging for 9 Very Bright, Spectroscopically Confirmed,

Group-scale Lenses

There are large samples of strong lenses that probe small (galaxy) scale

masses (e.g., SLACS, SQLS, COSMOS). There are also large samples of

strong lenses that probe large (rich cluster) scale masses (e.g.,

various rich Abell clusters, the Hennawi et al. 2008 SDSS sample). The

sample of strong lenses that probe intermediate (group/cluster-core)

scale masses, however, is sparse, and so any significant additions to

this sample are important. Here we present a sample of strong lenses

that not only probe these intermediate scales but are also quite bright,

since the sample is based almost entirely upon data from the SDSS, a

relatively shallow and poor-resolution survey, at least in comparison to

most other strong lens hunting grounds, such as COSMOS and CFHTLS. What

we lack are the high-resolution imaging data needed to construct

detailed lensing models, to probe the mass and light profiles of the

lensing galaxies and their environments, and to characterize the

morphologies of the lensed (source) galaxies. Only HST can provide these

data, and so we are proposing here for 81 orbits of deep WFPC2 F450W,

F606W and F814W imaging, for 9 of our best and brightest

intermediate-scale lensing systems with known spectroscopic redshifts

and with Einstein radii between 4 and 8 arcsec.

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 11979

WFPC2 Imaging of Fomalhaut b: Determining its Orbit and Testing for

H-alpha Emission

Fomalhaut is a bright nearby star that harbors a belt of dusty material

with a morphology that has been used to predict the presence of a

shepherding planet. With ACS/HRC coronagraphy, we have achieved the

direct detection of a planet candidate (Fomalhaut b) in F606W and F814W.

The planet candidate lies 18 AU interior to the dust belt and we detect

counterclockwise orbital motion in two epochs of observations (2004 and

2006). Fomalhaut b has mass no greater than three Jupiter masses based

on an analysis of its luminosity, including non-detections at infrared

wavelengths, and the dynamical argument that a significantly more

massive object would disrupt the dust belt. Variability at optical

wavelengths and the brightness in the F606W passband suggest additional

sources of luminosity such as starlight reflected from a circumplanetary

ring system. A second possibility that has been invoked for substellar

objects is a significant contribution of H-alpha emission. Here we

propose follow-up WFPC2 observations to test the possibility that the

F606W flux is contaminated by H-alpha emission. We demonstrate that the

detection of Fomalhaut b using WFPC2 is feasible using roll

deconvolution. Furthermore, a detection of Fomalhaut b in 2009 will

provide a crucial third epoch for astrometry. With the existing two

epochs of data, the orbit of Fomalhaut b cannot be determined uniquely.

The third epoch will be used to test the prediction of apsidal alignment

and more accurately determine the dynamical mass of Fomalhaut b. If

apsidal mis-alignment is found between the planet and the belt, this

result would point to the existence of still other planets lurking

unseen in the Fomalhaut system.

WFPC2 11981

FUV Imaging Survey of Galactic Open Clusters

We propose a WFPC2 FUV imaging survey of 6 Galactic open clusters with

ages ranging from 1 Myr to 300 Myr complemented with NUV/optical imaging

of the same fields. No such survey has ever been attempted before in the

FUV at the resolution of WFPC2 (indeed, no WFPC2 FUV images of any

Galactic open cluster exist in the HST archive) and, since WFPC2 will be

retired in SM4 and none of the other HST instruments can do FUV imaging

of bright objects, this is the last chance to do such a survey before

another UV telescope is launched. This survey will provide a new

perspective on young/intermediate age Galactic clusters and a key

template for the study of star formation at high redshift, where the

intensity peak we observe in the optical/NIR from Earth is located in

the FUV in its rest frame. For clusters still associated with an H II

region, UV imaging maps the continuum emission of the ionized gas and

the radiation scattered by background dust and, combined with optical

nebular images, can be used to determine the 3-D structure of the H II

region. For all young clusters, FUV+NUV+optical photometry can be used

to study the UV excesses of T-Tauri stars. For clusters older than ~40

Myr, the same photometric combination is the easiest method to detect

companion white dwarfs which are invisible using only the optical and

NIR. WFPC2 is also an excellent instrument to discover close companions

around bright stars and improve our knowledge of their multiplicity

fraction. Finally, for all clusters, the combination of

high-spatial-resolution UV and optical photometry can be used to

simultaneously measure the temperature, extinction, extinction law,

distance, and existence of companions (resolved and unresolved) and,

thus, produce clean HR diagrams with resolved cluster membership and

much-reduced systematic uncertainties.

WFPC2 11983

An Imaging Survey of Protoplanetary Disks and Brown Dwarfs in the

Chamaeleon I Region

We propose to carry out a HST/WFPC2 survey of young brown dwarfs, Class

I and Class II sources in the Chamaelon I region, one of the

best-studied star-forming regions, in order to investigate the link

between disk evolution and the formation of substellar-mass objects. We

will use deep broad-band imaging in the I and z-equivalent HST bands to

unveil the unknown population of substellar binary companions, down to a

few Jupiter masses for separations of a few tens of AU. We will also

perform narrow-band imaging to directly detect accreting circumstellar

disks and jets around brown dwarfs, Class-I and class-II objects.

Chamaelon I is nearly coeaval of Orion (~1-2Myr) but at ~1/3 its

distance, allowing 3x higher resolution and 10x more flux for comparable

objects. Unlike Orion, low-mass objects and protoplanetary disks in

Chamaeleon I have been extensively studied with Spitzer, but not yet

with the HST. The Chamaeleon I region is an ideal HST target, as it lies

in the CVZ of the HST and therefore it is easily accessible any time of

the year with long orbits.

WFPC2 11993

High Resolution Imaging of a Binary Supermassive Black Hole Candidate

Dithered high resolution images of a supermassive binary black hole

candidate SDSS J153636.22+044127.0 will be obtained with the WFPC2/PC in

F675W. This QSO was identified in November, 2008 by a principal

components analysis of the ~ 17, 500 QSOs in the SDSS DR7 sample. It is

unique among all known QSOs in having two broadline regions, indicative

of two supermassive black holes being actively fed. It is the best

candidate for a supermassive binary black hole known. Such binaries

should be common in the Universe and play key roles in the formation and

evolution of galaxies, yet no convincing examples had been identified

prior to this QSO. The HST imaging should be able to constrain two

alternative hypotheses that this object is 1) the site of a black hole

ejected from a nucleus by a multi-body interaction, or 2) a simple line

of sight superposition of two unrelated AGN. With the superb spatial

resolution of HST, two AGN separated by > 300pc (projected) should be

readily visible.

FLIGHT OPERATIONS SUMMARY:

Significant Spacecraft Anomalies: (The following are preliminary reports

of potential non-nominal performance that will be investigated.)

HSTARS:

11778 - GSAcq(2,1,1) scheduled at 112/06:48:30 failed at 112/06:52:40 due to

           search radius limit exceeded on FGS1.

           Observations affected: WFPC 141 - 148, Proposal ID# 11983.

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

                      SCHEDULED      SUCCESSFUL 

FGS GSAcq               09                 08  

FGS REAcq               05                 05                             

OBAD with Maneuver 22                  21   

SIGNIFICANT EVENTS: None