This week on HST

HST Programs: March 8, 2010 - March 14, 2010

Selected highlights

GO 11628: Globular Cluster Candidates for Hosting a Central Black Hole

Artist's impression of the visual distortions introduced by a black hole in a globular cluster

The formation, and subsequent evolution, of intermediate-mass black holes (IMBHs) is a process of considerable importance for understanding th development of active galactic nuclei at high redshifts. IMBHs are generally expected to originate in globular-cluster-mass structures; hence, one might expect such objects to be present in some present-day Galactic clusters, particularly those that have undergone dynamical core collapse. The present program aims to obtain detailed measurements of the central radial profiles of a number of globulars, searching for systems with weak cusps that might indicate the presence of central IMBH. The targets are globulars with high central concentrations, including NGC 5946, NGC 6256, NGC 6342 and NGC 6355

GO 11644: A dynamical-compositional survey of the Kuiper belt: a new window into the formation of the outer solar system

The architecture of the outer Solar System

The Kuiper Belt lies beyond the orbit of Neptune, extending from ~30 AU to ~50 AU from the Sun, and includes at least 70,000 objects with diameters exceeding 100 km. Setting aside Pluto, the first trans-Neptunian objects were discovered in the early 1990s. Most are relatively modest in size, with diameters of a few hundred km and photometric properties that suggested an icy composition, similar to Pluto and its main satellite, Charon. Over the last three years, a handful of substantially larger bodies have been discovered, with diameters of more than 1000 km; one of the objects, 2003 UB313, is comparable in size to Pluto (2320 km.). At the same time, ground-based surveys, such as the Deep Ecliptic Survey, the Canada-France Ecliptic plane Survey and the Palomar Quest Survey, scanned the ecliptic for fainter, lower-mass objects, with the aim of using their properties to assess the likely chemical composition and dynamical history of the early Solar System. The present program will use Wide Field Camera 3 to push up to 2 magnitudes fainter than these ground-based studies, providing reliable estimates of compositions for a representative sample of KBOs.

GO 11659: Probing the Interior of SN1006

Chandra X-ray image of the SN1006 supernova remnant

In May 1006, Chinese, Arabic and European astronomers and stargazers independently identified a "guest star" in the region of the sky that would become known as the constellation Lupus. The star exceeded Venus in brightness at its peak, even threatening to rival the Moon, and remained visible until at least the end of that year. Indeed, there are suggestions that there a secondary brightening that preserved the star at naked eye magnitude until early 1008. The associated remnant was not identified until 1965, when Milne and Gardner resolved the radio source PKS 1459-41 into a circular shell, approximately 30 arcminutes in diameter. That remnant has since been studied extensively, notably by the Chandra satellite. HST is clearly poorly suited to mapping the remnant. However, there are a number of bright UV sources that lie behind the remnant, and those can be use to probe the remnant. This proposal will use COS to obtain spectra of these three sources, and trace the chemical and physical properties of the gas based on the absorption line profiles.

GO 11721: Verifying the Utility of Type Ia Supernovae as Cosmological Probes: Evolution and Dispersion in the Ultraviolet Spectra

A recent supernova in M100

Supernovae are the most spectacular form of stellar obituary. In recent years, these celestial explosions have acquired even more significance through the use of Type Ia supernovae as distance indicators in mapping the `dark energy' acceleration term of cosmic expansion. However, while there is a well-established model for the two main types of supernovae, runaway fusion on the surface of a white dwarf in a binary system, there are still some uncertainties as to the uniformity of the events, and the consequence potential for systematic uncertainties in the distance estimates. One of the questionmarks comes from spectroscopy of a number of supernovae at intermediate redshift (z~0.5) that appears to show a substantial dispersion in properties at UV wavelengths. The present program aims to probe this issue by using STIS to obtain UV spectra of nearby supernovae, and therefore examining the detailed behaviour in the local universe.