HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT       #4784

PERIOD COVERED: 5am February 3 - 5am February 4, 2009 (DOY

                           034/1000z-035/1000z)

OBSERVATIONS SCHEDULED

ACS/SBC 11579

The Difference Between Neutral- and Ionized-Gas Metal Abundances in

Local Star-Forming Galaxies with COS

The metallicity of galaxies and its evolution with redshift is of

paramount importance for understanding galaxy formation. Abundances in

the interstellar medium (ISM) are typically determined using

emission-line spectroscopy of HII regions. However, since HII regions

are associated with recent SF they may not have abundances typical for

the galaxy as a whole. This is true in particular for star-forming

galaxies (SFGs), in which the bulk of the metals may be contained in the

neutral gas. It is therefore important to directly probe the metal

abundances in the neutral gas. This can be done using absorption lines

in the Far UV. We have developed techniques to do this in SFGs, where

the absorption is measured for sightlines toward bright SF regions

within the galaxy itself. We have successfully applied this technique to

a sample of galaxies observed with FUSE. The results have been very

promising, suggesting in I Zw 18 that abundances in the neutral gas may

be up to 0.5 dex lower than in the ionized gas. However, the

interpretation of the FUSE data is complicated by the very large FUSE

aperture (30 arcsec), the modest S/N, and the limited selection of

species available in the FUSE bandpass. The advent of COS on HST now

allows a significant advance in all of these areas. We will therefore

obtain absorption line spectroscopy with G130M in the same sample for

which we already have crude constraints from FUSE. We will obtain

ACS/SBC images to select the few optimal sightlines to target in each

galaxy. The results will be interpreted through line-profile fitting to

determine the metal abundances constrained by the available lines. The

results will provide important new insights into the metallicities of

galaxies, and into outstanding problems at high redshift such as the

observed offset between the metallicities of Lyman Break Galaxies and

Damped Lyman Alpha systems.

FGS 11942

Increasing the Accuracy of HST Astrometry with FGS1R

We propose to observe six exoplanetary system host stars and two

planetary nebulae central stars with FGS1r. All objects have been

previously observed under proposals GO-09233, -09969, -10989, and

-11210. These observations will significantly extend the time baseline,

permitting improvements in the determination of proper motion. This

systematic motion must be removed to get at the perturbation of

interest, either due to exoplanetary companions or the orbital motion of

the Earth (parallax). In most cases the perturbation orbits will also

improve. We improve either companion mass or PN parallax. For one

target, GJ 876, theoretical dynamical modelers have proposed an

inclination closer to 50 degrees, while FGS3 measurements indicated an

inclination closer to 84 degrees. These new data, once combined with our

older FGS3 data, will permit an independent remeasurement of the

inclination of the outermost companion, and a re-evaluation of widely

used dynamical algorithms.

NIC3 11236

Did Rare, Large Escape-Fraction Galaxies Reionize the Universe?

Lyman continuum photons produced in massive starbursts may have played a

dominant role in the reionization of the Universe. Starbursts are

important contributors to the ionizing metagalactic background at lower

redshifts as well. However, their contribution to the background depends

upon the fraction of ionizing radiation that escapes from the intrinsic

opacity of galaxies below the Lyman limit. Current surveys suggest that

the escape fraction is close to zero in most galaxies, even among young

starbursts, but is large in 15-25% of them. Non-uniform escape fractions

are expected as a result of violent events creating clear paths in small

parts of galaxies. The number of galaxies observed with high escape

fraction will result from the combination of the intrinsic number with

clear lines of sight and their orientation with respect to the observer.

We propose to measure the fraction of escaping Lyman continuum radiation

in a large sample (47) of z~0.7 starbursts in the COSMOS field. These

compact UV-luminous galaxies are good analogs to high redshift LBGs.

Using the SBC/PR130L we can quickly (1-4 orbits) detect relative escape

fractions (f_LC/f_1500) of 25% or more. This will be the first

measurement of the escape fraction in sources between z=1 and the local

universe. We expect ~10 detections. Stacking will set limits of <4% on

the relative escape fraction in the rest. We will correlate the LC

detections with the properties of the galaxies. By targeting z~0.7 in

COSMOS, we will have tremendous ancillary information on those sources.

A non-detection in all sources would be significant (99% confidence).

This would imply that QSOs provide the overwhelming majority of ionizing

radiation at z<1, requiring substantial evolution in the processes

within Lyman break galaxies which allow large escape fractions at high

redshift.

WFPC2 11787

Dynamical Masses and Radii of Four White Dwarf Stars

This proposal uses the FGS1r in TRANS mode to resolve a pair of double

degenerate binary systems {WD1639+153 and WD 1818+26} in order to

determine their orbital elements. In addition, the binaries and several

nearby field stars are observed by FGS1r in POS mode to establish the

local inertial reference frame of each binary, as well as its parallax

and proper motion. This will allow for a direct measurement of the

distance, which yields the instrinsic luminosity, and when combined with

the spectroscopic estimates of the T_eff, the radius of each of the four

WD stars. When combined with the orbital elements, this leads to a

dynamical mass measurement for each WD, and a four calibration points of

the WD mass-radius relation.;

WFPC2 11797

Supplemental WFPC2 CYCLE 16 Intflat Linearity Check and Filter Rotation

Anomaly Monitor

Supplemental observations to 11029, to cover period from Aug 08 to SM4.

Intflat observations will be taken to provide a linearity check: the

linearity test consists of a series of intflats in F555W, in each gain

and each shutter. A combination of intflats, visflats, and earthflats

will be used to check the repeatability of filter wheel motions.

(Intflat sequences tied to decons, visits 1-18 in prop 10363, have been

moved to the cycle 15 decon proposal 11022 for easier scheduling.)

Note: long-exposure WFPC2 intflats must be scheduled during ACS anneals

to prevent stray light from the WFPC2 lamps from contaminating long ACS

external exposures.

Note: These are supplemental observations to cover June to SM4 (Oct 8

'08) + 6 months.

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.

FLIGHT OPERATIONS SUMMARY:

Significant Spacecraft Anomalies: (The following are preliminary reports

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

HSTARS:

11662 – REacq(2,1,2) Failed due to Stop Flag @ 034/18:53:47z

            Observations affected: ACS 7 - 8 Proposal ID#11236

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

                       SCHEDULED      SUCCESSFUL 

FGS GSacq               10                  10                    

FGS REacq               03                  02                       

OBAD with Maneuver 20                  20               

SIGNIFICANT EVENTS: (None)