This week on HST

HST Programs: March 23 - March 29, 2009

Selected highlights

GO 10877: A Snapshot Survey of the Sites of Recent, Nearby Supernovae

A recent supernova in M100

Supernovae mark the (spectacular) evolutionary endpoint for a subset of stellar systems. Standard models predict that they originate from massive stars and (probably) close binaries with a compact (WD, neutron star) component, but there are still some questions remaining over whether we fully understand the range of possible progenitors. The last decade has seen the development of a number of large-scale programs, usually using moderate-sized telescopes, that are dedicated to monitoring (relatively nearby galaxies, searching for new supernovae. This program obtains follow-up images of recent supernovae, concentrating on systems within 20 Mpc of the Milky Way. The observations are taken well after maximum, with the aim of using the high spatial resolution of WFPC2 to identify the fading remnant and perhaps determine its origin.

GO 11972: Investigating the Early Solar System with Distant Comet Nuclei

The nucleus of Comet Borelly, as resolved by Deep Space 1

Comets are among both the least substantial and most spectacular inhabitants of the Solar System. They are believed to have played an important role in the early Solar System, delivering water to Earth shortly after its formation. Near the Sun, great comets can spawn tails that are millions of miles in length, stretching over tens of degrees. The source of that splendour is a small cometary nucleus, typically no more than 10-20 kilometres in size. The aim of the present program is to use WFPC2 to image eight dynamically new, long-period comets when they are at large distances from the Sun, and their activity levels are low. Those data will be used to estimate the sizes of the individual nuclei, providing information that can be fed into models used to predict thermal properties and outgassing behviours.

GO 11974: High-resolution imaging for 9 very bright, spectroscopically confirmed, group-scale lenses

Strong galaxian lens from the SLACS survey

Gravitational lensing provides a powerful method of tracing the mass distribution in both galaxy clusters and individual galaxies, while at the same time amplifying the light from background galaxies to allow detailed investigation of their properties. This proposal will obtain WFPC2 observations of a 9 strong lenses, identified from the ground-based Sloan Digital Sky Survey. By themselves, the SDSS data have neither sufficient resolution nor sensitivity to map the detailed structure of the lens, and hence the underlying galaxian potential. The aim is to combine the WFPC2 data with detailed models to measure the mass distribution and light profiles of the lensing galaxies, and constrain the morphological properties of the background lensed galaxy.

GO 11986: Completing HST's Local Volume Legacy

SIRTF image of NGC 2976 (from the SINGS program)

Colour-magnitude diagrams derived from photometric surveys have proven invaluable in developing our understanding of the main properties of the galactic stellar populations. Large ground-based telescopes allowed extension of this type of analysis to the principal satellites of the Milky Way and, to a limited extent, the Andromeda spiral. With the advent of HST, particularly following SM3B and the installation of the Advance Camera for Surveys, those fundamental CMD studies can be extended to higher-density star fields, fainter magnitudes and intrinsically lower luminosity stars. Until recently, studies have concentrated on nearer Local Group galaxies; the ambitious aim of the original incarnation of this program (Program GO 10915, The ACS Nearby Galaxy Survey) was to conduct a systematic survey of all major star-forming galaxies within ~3.5Mpc of the Milky Way, together with a number of galaxies in the M81 group at a distance of ~4 Mpc. That program included a total of 45 galaxies, ranging from massive spiral systems to dwarf galaxies. Initially, observations were made using the wide-field camera on ACS, sampling selected fields in the wide-V (F606W) and I (F814W) passbands. Following the ACS failure in January 2007, the program was re-designed, focusing on WFPC2 observations of the larger galaxies within ~3.5 Mpc, as program GO 11307: Completing the ACS Galaxy Survey with WFPC2.