HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT       #4841

PERIOD COVERED: 5am April 24 - 5am April 27, 2009 (DOY

                           114/0900z-117/0900z)

OBSERVATIONS SCHEDULED

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.

ACS/SBC 11982

Spanning the Reionization History of IGM Helium: a Large and Efficient

HST Spectral Survey of Far-UV-Bright Quasars

The reionization of IGM helium is thought to have occurred at redshifts

of z=3 to 4. Detailed studies of HeII Lyman-alpha absorption toward a

handful of QSOs at 2.7<z<3.3 demonstrated the high potential of such IGM

probes, but the small sample size and redshift range limit confidence in

cosmological inferences. The requisite unobscured sightlines to high-z

are extremely rare, but we've cross-correlated 10, 000 z>2.8 SDSS DR7

(and other) quasars with GALEX GR4 UV sources to obtain 550 new, high

confidence, sightlines potentially useful for HST HeII studies; and in

cycle 15-16 trials we demonstrated the efficacy of our SDSS/GALEX

selection approach identifying 9 new HeII quasars at unprecedented 67%

efficiency. We propose the first far-UV-bright HeII quasar survey that

is both large in scale and also efficient, via 2-orbit reconnaissance

ACS/SBC prism spectra toward a highly select subset of 40 new SDSS/GALEX

quasars at 3.1<z<5.1. These will provide a community resource list that

includes 5 far-UV-bright (restframe) HeII sightlines in each of 8

redshift bins spanning 3.1<z<3.9 (and perhaps several objects at z>4),

enabling superb post-SM4 follow-up spectra with COS or STIS. But

simultaneously and independent of any SM4 uncertainties, we will hereby

directly obtain 10-orbit UV spectral stacks from the 5 HeII quasars in

each of the 8 redshift bins to trace the reionization history of IGM

helium over at least 3.1<z<3.9. These spectral stacks will average over

cosmic variance and individual object pathology. Our new high-yield HeII

sightline sample and spectral stacks, covering a large redshift range,

will allow confident conclusions about the spectrum and evolution of the

ionizing background, the evolution of HeII opacity, the density of IGM

baryons, and the epoch of helium reionization.

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 11978

Luminous and Dark Matter in Disk Galaxies from Strong Lensing and

Stellar Kinematics

The formation of realistic disk galaxies within the LCDM paradigm is

still an unsolved problem. Theory is only now beginning to make

predictions for how dark matter halos respond to galaxy formation and

for the properties of disk galaxies. Measuring the density profiles of

dark matter halos on galaxy scales is therefore a strong test for the

standard paradigm of galaxy formation, offering great potential for

discovery. However, from an observational point of view, the degeneracy

between the stellar and dark matter contributions to galaxy rotation

curves remains a major road block. Strong gravitational lensing, when

coupled to spatially-resolved kinematics and stellar population models,

can solve this long-standing problem. Unfortunately, this joint

methodology could not be exploited so far due to the paucity of known

edge-on spiral lenses. Exploiting the full SDSS-DR7 archive we have

identified a new sample of exactly these systems. We propose multi-color

HST imaging to confirm and measure a sample of twenty spiral lenses,

covering a range of bulge to disk ratios. By combining dynamical lensing

and stellar population information for this unique sample we will

deliver the first statistical constraints on halos and disk properties,

and a new stringent test of disk galaxy formation theories.

WFPC2 11944

Binaries at the Extremes of the H-R Diagram

We propose to use HST/Fine Guidance Sensor 1r to survey for binaries

among some of the most massive, least massive, and oldest stars in our

part of the Galaxy. FGS allows us to spatially resolve binary systems

that are too faint to observe using ground-based, speckle or optical

long baseline interferometry, and too close to resolve with AO. We

propose a SNAP-style program of single orbit FGS TRANS mode observations

of very massive stars in the cluster NGC 3603, luminous blue variables,

nearby low mass main sequence stars, cool subdwarf stars, and white

dwarfs. These observations will help us to (1) identify systems suitable

for follow up studies for mass determination, (2) study the role of

binaries in stellar birth and in advanced evolutionary states, (3)

explore the fundamental properties of stars near the main sequence-brown

dwarf boundary, (4) understand the role of binaries for X-ray bright

systems, (5) find binaries among ancient and nearby subdwarf stars, and

(6) help calibrate the white dwarf mass - radius relation.

FGS 11943

Binaries at the Extremes of the H-R Diagram

We propose to use HST/Fine Guidance Sensor 1r to survey for binaries

among some of the most massive, least massive, and oldest stars in our

part of the Galaxy. FGS allows us to spatially resolve binary systems

that are too faint for ground-based, speckle or optical long baseline

interferometry, and too close to resolve with AO. We propose a

SNAP-style program of single orbit FGS TRANS mode observations of very

massive stars in the cluster NGC 3603, luminous blue variables, nearby

low mass main sequence stars, cool subdwarf stars, and white dwarfs.

These observations will help us to (1) identify systems suitable for

follow up studies for mass determination, (2) study the role of binaries

in stellar birth and in advanced evolutionary states, (3) explore the

fundamental properties of stars near the main sequence-brown dwarf

boundary, (4) understand the role of binaries for X-ray bright systems,

(5) find binaries among ancient and nearby subdwarf stars, and (6) help

calibrate the white dwarf mass - radius relation.

FGS 11790

HST/FGS Astrometric Search for Young Planets Around Beta Pic and AU Mic

AU Mic is a nearby Vega-type debris disk star. Its disk system has been

spatially resolved in exquisite detail, predominantly via the ACS

coronagraph and WFPC-2 cameras onboard HST. These images exhibit a

wealth of morphological features which provide compelling indirect

evidence that AU Mic likely harbors short-period planetary body(ies). We

propose to use the superlative astrometric capabilities of HST/FGS to

directly detect these planets, hence provide the first direct planet

detection in a Vega-type system whose disk has been imaged at high

spatial resolution.

FGS 11704

The Ages of Globular Clusters and the Population II Distance Scale

Globular clusters are the oldest objects in the universe whose age can

be accurately determined. The dominant error in globular cluster age

determinations is the uncertain Population II distance scale. We propose

to use FGS 1r to obtain parallaxes with an accuracy of 0.2

milliarcsecond for 9 main sequence stars with [Fe/H] < -1.5. This will

determine the absolute magnitude of these stars with accuracies of 0.04

to 0.06mag. This data will be used to determine the distance to 24

metal-poor globular clusters using main sequence fitting. These

distances (with errors of 0.05 mag) will be used to determine the ages

of globular clusters using the luminosity of the subgiant branch as an

age indicator. This will yield absolute ages with an accuracy 5%, about

a factor of two improvement over current estimates. Coupled with

existing parallaxes for more metal-rich stars, we will be able to

accurately determine the age for globular clusters over a wide range of

metallicities in order to study the early formation history of the Milky

Way and provide an independent estimate of the age of the universe.

The Hipparcos database contains only 1 star with [Fe/H] < -1.4 and an

absolute magnitude error less than 0.18 mag which is suitable for use in

main sequence fitting. Previous attempts at main sequence fitting to

metal-poor globular clusters have had to rely on theoretical

calibrations of the color of the main sequence. Our HST parallax program

will remove this source of possible systematic error and yield distances

to metal-poor globular clusters which are significantly more accurate

than possible with the current parallax data. The HST parallax data will

have errors which are 10 times smaller than the current parallax data.

Using the HST parallaxes, we will obtain main sequence fitting distances

to 11 globular clusters which contain over 500 RR Lyrae stars. This will

allow us to calibrate the absolute magnitude of RR Lyrae stars, a

commonly used Population II distance indicator.

WFPC2 11316

HST Cycle 16 & Pre-SM4 Optical Monitor

This is a continuation of the Cycle 15 & pre-SM4 Optical Monitor, 11020.

Please see that proposal for a more complete description of the

observing strategy. The 6 visits comprising this proposal observe two

single standard stars with WFPC2/PC in order to establish overall OTA

focal length for the purposes of focus maintenance. The goal of this

monitoring before SM4 is to establish a best estimate of the OTA focus

entering SMOV.

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.

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               23                  23

FGS REAcq               15                  15                           

OBAD with Maneuver 72                  72                

SIGNIFICANT EVENTS: (None)