This week on HST

HST Programs: February 18 - February 24, 2008

Some selected highlights

GO 11120: A Paschen-Alpha Study of Massive Stars and the ISM in the Galactic Center

A multi-wavelength composite image of the Galactic Centre (red - 90 cm radio data; green, mid-IR data; blue, X-ray)

The Galactic Centre lies in the heart of the constellation of Sagittarius, and at a distance of ~8 kiloparsecs from the Sun. Galactic nuclei are the likely end-point for mass accretion, and are generally the site of highly energetic activity; the Galactic Centre is no exception. AO near-infrared imaging has been brought to bear on this issue, resolving a number of stars within the core, close to the compact radio source Sagittarius A*. Monitoring of those sources over the last decade has shown that they are in rapid orbital motion around a very massive central object, now clearly identified as a ~3 million solar-mass black hole. Moving beyond the core, to distances of tens of parsecs from centre, observations have revealed molecular gas and young star forming regions. The aim of the present proposal is to use the NICMOS NIC3 camera to survey a ~32 x 13 arcminute region (~75 pc x 30 pc) in two narrowband filters: F187N, ceentred on the Paschen alpha line; and F190N, providing the continuum flux. These obbservations will provide a detailed map of the star forming activity within the Galactic nucleus.

GO 11181: SAINTS - Supernova 1987A INTensive Survey

November 2003 HST image of the SN1987A gaseous ring

SN1987A, in the Large Magellanic Cloud, was the first naked-eye supernova since Kepler's supernova of 1604. While its eruption, in January 1987, predated HST's launch by over 3 years, the remnant has been a regular observational target. Those high resolution observations have revealed the development, and evolution, of extensive, intricate structures as the blast wave from SN1987A encounters the surrounding interstellar medium. In particular, a striking circum-remnant ring has developed, with numerous hot spots stimulated by the fastest moving debris. The present HST program continues to monitor the development of those features through Cycle 16, using a series of observations that are co-ordinated with both the Chandra X-ray Observatory and Spitzer. During the present cycle, the hotspots may fuse, as the shock fully enters the ring, and photons from these regions may excite previously hidden gas outside the ring, illuminating mass lost from the progenitor before the explosion. The inner debris are now well resolved, and clearly asymmetrical. Overall, these observations provide crucial insight into the earliest stages of formation of a supernova remnant.

GO 11196: An Ultraviolet Survey of Luminous Infrared Galaxies in the Local Universe

A NICMOS image of the interacting LIRG, NGC 6090

Luminous infrared galaxies (LIRGs) have total luminosities that exceed 1011.4 LSun, 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 builds on a previous ACS survey of 88 systems from the IRAS Revised Bright Galaxy Sample (GO 10592) in the F439W and F814W passbands. The present program is using the ACS/SBC and WFPC2 to obtain far- (F140LP) and near- (F218W) UV imaging of 27 galaxies. Combined with the previously obtained B- and I-band data, these observations will probe the distribution of star formation activity and the presence of bars and bridges, funneling gas towards active regions the age distribution of star clusters the relationship between star formation and AGN activity the overall structural properties of the LIRGS as a function of luminosity and environment The observations will also provide a detailed UV images for a reference sample of nearby galaxies. Observations of the interacting system, NGC 17, are scheduled for this week.

GO 11213: Distances to Eclipsing M Dwarf Binaries

Artist's impression of a cool binary system

Eclipsing binaries are stellar systems where the orbital plane lies in the line of sight, leading to the components undergoing mutual eclipses. These systems are extremely powerful probes of stellar properties, since (given the appropriate radial velocity measurements) they permit direct measurement of both stellar masses and radii. Accurate distances can also be derived from these systems. These results are particularly interesting for stars near the bottom of the main sequence, approaching the hydrogen buyrning limit. The present program aims to use the Fine Guidance Sensors on HST to determine sub-milliarcsecond trigonometric parallaxes for five M-dwarf binaries: YY Gem, GU Boo, CM Dra, NSVS0103 and TRES-HER0-R