Status Report

NASA Hubble Space Telescope Daily Report #4825

By SpaceRef Editor
April 8, 2009
Filed under , ,


Continuing to collect World Class Science

PERIOD COVERED: 5am April 2 – 5am April 3, 2009 (DOY 092/0900z-093/0900z)


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 11603

A Comprehensive Study of Dust Formation in Type II Supernovae with HST, Spitzer and Gemini

The recent discovery of three extremely bright Type II SNe, (2007it, 2007oc, 2007od) gives us a unique opportunity to combine observations with HST, Spitzer and Gemini to study the little understood dust formation process in Type II SNe. Priority 1 Spitzer Cycle 5 and band 1 Gemini 2008A time has already been approved for this project. Since late-time Type II SNe are faint and tend to be in crowded fields, we need the high sensitivity and high spatial resolution of ACS/HRC and NICMOS/NIC2 for these observations. This project is motivated by the recent detection of large amounts of dust in high redshift galaxies. The dust in these high-z galaxies must come from young, massive stars so Type II SNe could be potential sources. The mechanism and the efficiency of dust condensation in Type II SN ejecta are not well understood, largely due to the lack of observational data. We plan to produce a unique dataset, combining spectroscopy and imaging in the visible, near- and mid-IR covering the key phase, 400-700 days after maximum when dust is known to form in the SN ejecta. Therefore, we are proposing for coordinated HST/NOAO observations (HST ACS/HRC, NICMOS/NIC2 & Gemini/GMOS and TReCS) which will be combined with our Spitzer Cycle 5 data to study these new bright SNe. The results of this program will place strong constraints on the formation of dust seen in young high redshift (z>5) galaxies.

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 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 11975

UV Light from Old Stellar Populations: a Census of UV Sources in Galactic Globular Clusters

In spite of the fact that HST has been the only operative high-resolution eye in the UV-window over the last 18 years, no homogeneous UV survey of Galactic globular clusters (GGCs) has been performed to date. In order to fill this gap in the stellar population studies, we propose a program that exploits the unique capability of the WFPC2 and the SBC in the far-/mid- UV for securing deep UV imaging of 46 GGCs. The proposed observations will allow to study with unprecedented accuracy the hottest GGC stars, comprising the extreme horizontal branch (HB) stars and their progeny (the so-called AGB-manque’, and Post-early AGB stars), and “exotic stellar populations” like the blue straggler stars and the interacting binaries. The targets have been selected to properly sample the GGC metallicity/structural parameter space, thus to unveil any possible correlation between the properties of the hot stellar populations and the cluster characteristics. In addition, most of the targets have extended HB “blue tails”, that can be properly studied only by means of deep UV observations, especially in the far-UV filters like the F160BW, that is not foreseen on the WFC3. This data base is complemented with GALEX observations in the cluster outermost regions, thus allowing to investigate any possible trend of the UV-bright stellar types over the entire radial extension of the clusters. Although the hottest GGC stars are just a small class of “special” objects, their study has a broad relevance in the context of structure formation and chemical evolution in the early Universe, bringing precious information on the basic star formation processes and the origin of blue light from galaxies. Indeed, the proposed observations will provide the community with an unprecedented data set suitable for addressing a number of still open astrophysical questions, ranging from the main drivers of the HB morphology and the mass loss processes, to the origin of the UV upturn in elliptical galaxies, the dating of distant systems from integrated light, and the complex interplay between stellar evolution and dynamics in dense stellar aggregates. In the spirit of constructing a community resource, we entirely waive the proprietary period for these observations.


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


11759 – GSAcq (1,2,1) scheduled at 092/12:48:25z and REAcq (1,2,1) scheduled at 092/14:21:50z both failed with QF1STOPF and QSTOP flags set.

Observations affected: WFPC 109-120, Proposal ID# 11603.

11761 – REAcq (1,2,2) scheduled at 092/22:41:12z failed at 092/22:45:38z due to FGS Sequential Attitude update being too large to correct.

Observations affected: WFPC 127-129, proposal ID# 11975.

11762 – REAcq (1,2,2) scheduled from 093/03:40:52z – 03:48:20 failed due to FGS Sequential Attitude update being too large to correct.

Observations affected: WFPC 137-138, Proposal ID# 11975.



                        SCHEDULED      SUCCESSFUL

FGS GSAcq               05                   04
FGS REAcq               07                   04
OBAD with Maneuver      22                   22


SpaceRef staff editor.