Some selected highlights

GO 11079: Treasury Imaging of Star Forming Regions in the Local Group: Complementing the GALEX and NOAO Surveys \

The star forming region, N11, in the Small Magellanic Cloud

Star formation is a complex process that takes place on many scales, from diffuse, low-level activity within dispersed clouds like the nearby Taurus association, through massive star forming regions, like Orion and 30 Doradus, to intense starbursts within galactic nucle and mergers. The aim of the present proposal is to use WFPC2 to survey a representative sample of active star-forming regions in local Group galaxies. In particular, the observations will cover a wide range of OB associations in the two nearest large spirals, the Andromeda galaxy, M31, and the Triangulum system, M33. Multicolour, high-resolution images, taken at passbands from the ultraviolet (F170W) to far-red (F814W) will allow H-R diagrams to be constructed, probing the distribution of ages and metallicities, and setting constraints on variations in the underlying initial mass function(s). In the coming week, observations are scheduled of OB associations in the M33.

GO 11113: Binaries in the Kuiper Belt: Probes of Solar System Formation and Evolution

A composite of HST images of the Kuiper Belt binary, WW31

The Kuiper Belt consists of icy planetoids that orbit the Sun within a broad band stretching from Neptune's orbit (~30 AU) to distance sof ~50 AU from the Sun (see David Jewitt's Kuiper Belt page for details). Over 500 KBOs are currently known out of a population of perhaps 70,000 objects with diameters exceeding 100 km. Approximately 2% of the known KBOs are binary (including Pluto, one of the largest known KBOs, regardless of whether one considers it a planet or not). This is a surprisingly high fraction, given the difficulties involved in forming such systems and the relative ease with which they can be disrupted. It remains unclear whether these systems formed from single KBOs (through collisions or 3-body interactions) as the Kuiper Belt and the Solar System have evolved, or whether they represent the final tail of an initial (much larger) population of primordial binaries. This proposal will use WFPC2 imaging of known KBOs to identify new binary systems.

GO 11142: Revealing the Physical Nature of Infrared Luminous Galaxies at 0.3

NICMOS image of the nearby luminous IR galaxy, Arp 299

Luminous infrared galaxies (LIRGs) have total luminosities that exceed 10^11.4 L_Sun, with most of the energy emitted at wavelengths longward of 10 microns. Many (perhaps most) of these galaxies are interacting or merging disk galaxies, with the excess infrared luminosity generated by warm dust associated with the extensive star formation regions. Many systems also exhibit an active nucleus, and may be in the process of evolving towards an S0 or elliptical merger remnant. The present program is targeting systems with redshifts in the range 0.3 < z < 2.7, combining imaging at near-infrared (NICMOS on HST) and mid-infrared (MIPS on Spitzer) wavelengths. All of the systems already have Spitzer mid-infrared spectra, allowing not only an accurate characterisation of the over all flux distribution, and a \ determination of the total luminosity, but also providing insight into the galaxian dust content and chemical evolution.

GO 11361: Hubble Heritage Observations of Mars at 2007 Opposition

HST images of Mars oppositions over the last decade

Mars lies at an average distance of 228 million kilometres, or 1.52 AU, from the Sun, and has an orbital period of 687 days. As a result, it comes into opposition with Earth (i.e. the Sun, Earth and Mars lie along a str\ aight line) once every 780 days, or approximately every 2 years. At that time, Mars makes its closest approach, but the actual distance varies significantly from opposition to opposition since the Martian orbit has significant eccentricity (e=0.093, as compared with e=0.007 for Earth). HST has been systematically observing Mars at opposition since February 1995, 15 months after WFPC2 was installed in Servicing Mission 1. At that time, the planet lay at a distance of 101 million kilometres from Earth and subtended a diameter less than 14 arcseconds. Succeeding oppositions were at increasingly smaller separations, until the opposition of August 28 2003, when Mars was only 55.8 million miles away with an angular diameter of 25.1 arcseconds, its closest approach since 57,617 BCE (but we won't have to wait quite so long - Mars passes even closer on August 28 2287). As in past years, HST will take a series of images of Mars as it approaches opposition, which, this year, will be at 19:47 UT (2:47 pm EST) on Christmas Eve. At that time, Mars will lie at a distance of 88.2 million kilometres with a diameter of 15.2 arcseconds.