HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT       #4822

PERIOD COVERED: 5am March 30 - 5am March 31, 2009 (DOY

                           089/0900z-090/0900z)

OBSERVATIONS SCHEDULED

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 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 11593

Dynamical Masses of the Coolest Brown Dwarfs

T dwarfs are excellent laboratories to study the evolution and the

atmospheric physics of both brown dwarfs and extrasolar planets. To

date, only a single T dwarf binary has a dynamical mass determination,

and more are sorely needed. The prospects of measuring more dynamical

masses over the next decade are limited to 6 known short-period T dwarf

binaries. We propose here to obtain Long-Term HST/ACS monitoring for the

3 of the 6 binaries which cannot be resolved with AO from the ground.

Upon completion, our program will substantially increase the number of T

dwarf dynamical mass measurements and thereby provide key benchmarks for

testing theoretical models of ultracool objects.

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.

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 11977

WFPC2 12-Year Proper Motions of Two Galactic Analogs of the SN1987A

Rings

This special call in Cycle 16 is a unique opportunity to measure

fine-scale proper motions with the same WFPC2 camera after more than a

decade has elapsed, and is the last time such an opportunity is likely

to be available. We aim to apply this powerful tool to the ring nebulae

around two hot supergiants: the set of ionized double-rings around the

massive eclipsing binary RY Scuti, and the equatorial ring and bipolar

lobes around Sher 25. These are the only two Galactic analogs of SN1987A

for which this proper motion measurement is possible (others lack a

first-epoch image with HST, and SN1987A is too distant). In the case of

RY Scuti, the expected motions are small because the compact ring nebula

is only 1-arcsec in diameter. For Sher 25 the expected motions are small

because the object is thought to be at d=6 kpc. The 10-12 years that

have elapsed since earlier imaging epochs for these sources make it

possible to accurately measure their expected sub-pixel proper motion,

and hence, their ages and distances. We can discriminate between

specific proposed models for the formation of these ring nebulae by

measuring the relative ages of these ionized equatorial rings compared

to outer structures: the bipolar lobes in the case of Sher 25, and an

outer dust shell in the case of RY Scuti. These will provide the first

quantitative tests of binary merger vs. rapidly rotating single star

models for the shaping of SN1987A and related ring nebulae around

massive stars, which until now have relied upon qualitative comparisons

to structues seen in single-epoch images. The expected expansion is less

than 0.1 arcsec, so there is no hope of making either measurement from

the ground, and increased systematic errors associated with switching to

new instruments (with different pixel scales and distortion corrections)

will make this measurement more difficult even for HST after SM4.

FLIGHT OPERATIONS SUMMARY:

Significant Spacecraft Anomalies: (The following are preliminary reports

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

HSTARS:

11747 - GSAcq(1,2,1) at 089/13:08:31 and REAcq(1,2,1) at 089/14:22:48

           both failed to fine lock backup on FGS 1.

           Observations possibly affected: WFPC 23 - 30, Proposal ID# 11977.

11748 - GSAcq(1,3,1)scheduled for 090/00:28:00 failed due search radius

           limit exceeded on FGS1 at 090/00:32:54.

           REAcq(1,3,1) scheduled for 090/00:57:01 failed due search radius limit

           exceeded on FGS1 at 090/01:01:45.

           Observation affected: WFPC 37 - 39, Proposal ID# 11593

11749 - GSAcq(2,3,2) scheduled from 090/05:25:47 - 05:33:52 resulted in

           fine lock backup (2,0,2) using FGS-2 due to (QF3STOPF) and (QSTOP) stop

           flag indications on FGS-3.

           Observation possibly affected: Astrometry Proposal ID# 11944.

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

                      SCHEDULED      SUCCESSFUL

FGS GSAcq               06                 05          

FGS REAcq               06                 05            

OBAD with Maneuver 18                 18              

SIGNIFICANT EVENTS: (None)