This week on HST

HST Programs: January 19, 2008 - January 25, 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 11788: The Architecture of Exoplanetary Systems

Artist's impression of a young planetary system

Immanuel Kant is generally credited with first proposing that the planets in the Solar System coalesced from a flat, rotating disk formed by the Solar Nebula. Direct confirmation of that process only came in the early 1990s, when millimetre-wave interferometers were able to detect molecular gas in Keplerian rotation around a handful of nearby young stars. Since then, there have been numerous other observations, including Hubble's images of proplyds (protoplanetary disks) in the Orion Cluster, and Hubble and Spitzer observations of edge-on disks in other young stars. One of the clear selling points of the Solar Nebula disk model is that it appears to offer a natural path to forming planets with coplanar orbits, matching (most of) our observations of the Solar System. On the other hand, as our knowledge of exoplanetary systems has accumulated over the last decade, it has become clear that dynamical interactions may play a very important role in the evolution of these systems. In particular, disk/planet interactions are generally regarded as responsible for the inward migration of gas giants to form hot Jupiters in <3 day period orbits. Planet-planet interactions could lead to significant changes in orbital inclination. Radial velocity planet searches are uncovering more and more multi-planet systems. This program focuses the high precision of HST's astrometric detectors, the Fine Guidance Sensors, on four of those systems. The aim is to complement the existing radial velocity measurements with sub-milliarcsecond precision astrometry, allowing determination of the true orbital paths - specifically, the relative inclination - of the low-mass objects in these systems.

GO 11970: HST Observations of Titan's Escaping Atmosphere in Transit and in Emission

Saturn's satellite, Titan, as seen from Cassini

Titan and Saturn undergo a series of mutual phenomena every ~20 years, when Titan's orbit carries it across the body of the planet as viewed from earth. These phenomena have been taking place over the past couple of years, as Titan's ring plane aligns with the terrestrial viewpoint, but they will come to an end in late 2009. During these transits, Titan, and Titan's atmosphere, will be silhouetted against the Saturnian disk, allowing the potential detection of structure within the satellite's atmosphere. HST has the opportunity to observe Titanian transits on three occasions this year - January 23rd, February 8th and February 24th. The present observations focus on the first transit The ACS/SBC will be used to obtain images in the F115LP, F125LP and F140LP filters, both during the transit and away from transit. In the latter case, the observations will be used to search for atmospheric emission, primarily by Lyman alpha.