Status Report

NASA Hubble Space Telescope Daily Report #4791

By SpaceRef Editor
February 16, 2009
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Continuing to collect World Class Science

PERIOD COVERED: 5am February 12 – 5am February 13, 2009 (DOY 043/1000z-044/1000z)


ACS/SBC 11970

HST Observations of Titan’s Escaping Atmosphere in Transit and in Emission

We propose UV observations using the ACS/SBC of Titan’s extended escaping atmosphere for the Jan/Feb 2009 period of transits of Titan across Saturn. A combination of absorption of Saturn’s reflected solar UV emission in transit, and extended emissions primarily from H atoms away from transit, will yield new information about the structure of Titan’s extended upper atmosphere. These observations are expected to provide new constraints on theoretical models for a hydrodynamic flow of species through Titan’s exobase level, resulting from the interpretation of recent Cassini measurements at Titan.

FGS 11788

The Architecture of Exoplanetary Systems

Are all planetary systems coplanar? Concordance cosmogony makes that prediction. It is, however, a prediction of extrasolar planetary system architecture as yet untested by direct observation for main sequence stars other than the Sun. To provide such a test, we propose to carry out FGS astrometric studies on four stars hosting seven companions. Our understanding of the planet formation process will grow as we match not only system architecture, but formed planet mass and true distance from the primary with host star characteristics for a wide variety of host stars and exoplanet masses.

We propose that a series of FGS astrometric observations with demonstrated 1 millisecond of arc per-observation precision can establish the degree of coplanarity and component true masses for four extrasolar systems: HD 202206 (brown dwarf+planet); HD 128311 (planet+planet), HD 160691 = mu Arae (planet+planet), and HD 222404AB = gamma Cephei (planet+star). In each case the companion is identified as such by assuming that the minimum mass is the actual mass. For the last target, a known stellar binary system, the companion orbit is stable only if coplanar with the AB binary orbit.

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 11967

WFPC2 Imaging of the Lockman Hole

In order to understand galaxy evolution and constrain theoretical models, we require both multiwavelength photometry (to robustly determine physical parameters such as star formation rates and stellar masses) and detailed morphological information. Galaxy morphology encodes crucial information about galaxy formation history and the physical processes that trigger star formation and AGN activity, and high-resolution imaging for large samples of galaxies is currently only obtainable with HST. The Lockman Hole has been the target of extensive multi-wavelength observations from the X-ray to the radio, and will be the target of the deepest wide-area blankfield thermal IR observations with Herschel, but currently lacks comprehensive HST imaging. We propose to obtain WFPC2 imaging of ~500 arcmin2 of the central region of the Lockman Hole in F606W and F814W, to a depth of V606~26.8 and I814~26. This imaging is crucial in order to characterize the sources detected at other wavelengths.

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


Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.)

HSTARS: (None)



                        SCHEDULED      SUCCESSFUL
FGS GSacq               08                  08
FGS REacq               06                  06
OBAD with Maneuver      28                  28


SpaceRef staff editor.