This week on HST

HST Programs: October 5 - October 11, 2009

Selected highlights

GO 11205: The Effects of Multiplicity on the Evolution of Young Stellar Objects: A NICMOS Imaging Study

Millimetre-wave radio map of the Orion molecular clouds

The Orion association is the largest nearby star-forming complex, providing a key laboratory for unlocking the secrets of star formation. As such, it has been subject to intense scrutiny at all wavelengths from both ground and space. Surveys at near-infrared and mid-infrared wavelenths, notably by Spitzer, have identified an extensive number of embedded sources, young stellar objects (YSOs) that are still accreting from the surrounding molecular gas. This proposal focuses on one section of the Orion B molecular cloud: a filamentary structure near NGC 2068, a prominent reflection nebula. The goal is to investigate the degree of binarity of YSOs in this complex, probing a range of environments. Originally, NICMOS was used to survey a subset of the candidate YSOs in this region. These observations are an excellent complement to Spitzer since, while the HST IR cameras cannot offer either the same areal coverage or sensitivity at mid-infrared wavelengths, both NIC1 and WFC3-IR provide angular resolution better than 0.15 arcseconds, an order of magnitude higher than the Spitzer images.

GO 11565: A search for astrometric companions to very low-mass, Population II stars

HST image of Gliese 623AB, a nearby disk-dwarf binary system

Binary stars provide an important avenue for setting constraints on stellar evolution, particularly binary stars that consist of components with significantly different masses. The simplest means of producing stars in a dynamically bound system is during the formation process; consequently, it is reasonable to assume that the the stars are coeval and a comparison between the observed properties and predictions can constrain stellar models. Binary systems are common in stars in the Galactic disk, although the overall frequency does decrease with stellar mass, ranging from ~60-70% for G dwarfs to closer to 20% for late-type M dwarfs and ultracool dwarfs. Binaries are much rarer among the metal-poor members of the Galactic halo, with only a handful known among cool, late-type subdwarfs. The present program aims to expand the sample by using WFC3 on HST to image low-mass, metal-poor subdwarfs within 120 parsecs of the Sun, searching for close, faint companions that can be monitored for astrometric orbit determinations.

GO 11806: Coordinated Observations of LCROSS Impacts

LCROSS heads for the lunar surface

NASA's Lunar CRater Observation and Sensing Satellite ( LCROSS ) mission was launched in tandem with the Lunar Reconnaisance Observer (LRO) on June 18th this year. LCROSS and LRO are currently in polar orbit of the Moon, together with the Centuar rocket final stage, and LRO is conducting extensive mapping of the lunar surface. The prime aim of the LCROSS mission is to investigate whether water is present, as ice, in permanently shadowed areas near the lunar poles. To achieve that goal, the mission will send the Centaur final stage crashing into a lunar crater near the pole, producing a substantial plume of debris. Those debris will be observed by a Shepherding Spacecraft, which will track behind the Centaur before impacting itself. The crater chosen for the impact is Cabeus, a ~98 km diameter crater that lies within 100 km of the Moon's South Pole. Observations of that crater by LRO, Lunar Prospector and the Chandrayaan-1 and Kaguya spacecraft indicate a strong hydrogen concentration, suggestive of the presence of water ice. Any ice should vaporise when the Centaur impacts, and instruments on board the Shepherding Spacecraft, together with a wide variety of ground- and space-based observatories, including HST, will search for evidence of water. The LCROSS impact is scheduled for Friday October 9th at 7:30 am EDT/ 4:30 am PDT.