Status Report

NASA Hubble Space Telescope Daily Report #4795

By SpaceRef Editor
February 21, 2009
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Continuing to collect World Class Science

PERIOD COVERED: 5am February 19 – 5am February 20, 2009 (DOY 050/1000z-051/1000z)


WFPC2 11590

Observing the IR Catastrophe in a Deflagration Type Ia Supernova

Our lack of understanding of Type Ia supernova (SN Ia) explosions limits our confidence in their use for cosmology. While there is broad agreement that these objects represent the explosions of white dwarfs, the details of the explosion mechanism are not well-understood. Recently, we have identified an internally homogeneous subclass of SNe Ia whose photometric and spectroscopic peculiarities make them quite distinct from normal SNe Ia. Models suggest we may be seeing the result of an explosion with a subsonic burning front, called a deflagration. We propose to test SN Ia models by obtaining late-time photometry for SN 2008A, a recent, nearby example of this subclass, using ACS and WFC3 on HST. We will accurately measure the late-time photometric decline rate and spectral energy distribution (SED). These observations will allow us to test whether the ejecta contain the large amount of oxygen predicted by certain models. We also aim to detect major evolution of the SED expected due to the “IR catastrophe, ” a change in the dominant cooling mechanism in the ejecta, as generically predicted by models but only hinted at by current observations.

FGS 11944/11943

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 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 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.)


#11688 REAcq (2,1,2) Loss of Lock while guiding under two FGS during LOS @050/17:25z

Observations possibly affected: WFPC #117-118, Proposal ID #11986.



                            SCHEDULED      SUCCESSFUL           

FGS GSAcq                   06                    06
FGS REAcq                   07                    07
OBAD with Maneuver          26                    26
LOSS of LOCK                                                   


SpaceRef staff editor.