This week on HST

HST Programs: May 12 - May 18, 2014

Selected highlights

GO 13301: Deep COS Spectra of the Two Brightest Quasars that Probe the He II Post-Reionization Era

an HST GHRS spectrum of the bright quasar, HE 2347-4342

In astronomy, 'reionisation" usually refers to the period in the early universe (6 < z < 10) when star formation and/or accreting supermassive black holes produced sufficient ultraviolet flux to ionise hydrogen and lift the veil of the cosmic dark ages. However, intergalactic helium remained neutral at that time. The reionisation epoch for intergalactic helium is thought to occur somewhere between redshifts 3 and 4. Tracking the onset of that epoch through analysis of the He II Lyman alpha absorption constrains the evolution of star formation in the univers at those epochs. Observations, however, are complicated by the continued presence of neutral hydrogen, which absorbs radiaton at those wavelengths. The present program is using the Cosmic Origins Spectrograph to obtain deep observations of two of the brightest known He II quasars, HE2347-4342 and HS1700+6416. Both have previous UV spectroscopic observations by HST, as witnessed by the GHRS spectrum, but the new COS observations will be orders of magnitude more sensitive and can resolve individual He II absorption lines for comparison with neutral hydrogen and metal lines (C IV, Si IV). Inded, these observations will set a new benchmark for QSO absorption line studies with COS.

GO 13352: WISP - A Survey of Star Formation Across Cosmic Time

A region of massive star formation

Star formation is the key astrophysical process in determining the overall evolution of galactic systems, the generation of heavy elements, and the overall enrichment of interstellar and intergalactic material. Tracing the overall evolution through a wide redshift range is crucial to understanding how gas and stars evolved to form the galaxies that we see around us now. The present program builds on the ability of HST to carry out parallel observations, using more than one instrument. While the Cosmic Origins Spectrograph is focused on obtaining ultraviolet spectra of unparalleled signal-to-noise, this program uses the near-infrared grisms mounted on the Wide-Field Camera 3 infrared channel to obtain low resolution spectra between 1 and 1.6 microns of randomly-selected nearby fields. The goal is to search for emission lines characteristic of star-forming regions. In particular, these observations are capable of detecting Lyman-alpha emission generated by star formation at redshifts z > 5.6. A total of up to 40 "deep" (4-5 orbit) and 20 "shallow" (2-3 orbit) fields will be targeted in the course of this observing campaign.

GO 13503: Searching for Satellites of Ceres: Support for the Dawn Mission

HST images of the dwarf planet, Ceres

Ceres is one of the largest members of the main belt asteroids. Indeed, Ceres was the first such object discovered, by Giuseppe Piazzi in the coruse of his 1801 survey for a new planet that might fill out the Titius-Bode numerical sequence. Roughly spherical, with a diameter of 950 km, Ceres has been studied extensively from both ground and space. It is also targeted for study by NASA's DAWN mission, launched on September 27 2007. Dawn previously encountered the asteroid Vesta in August 2011, mapping the surface from a low altitude orbit which it maintained through September 5 2012. At that point the spacecraft used its xenon-ion engine to leave orbit and head for Ceres, where it is expected to arrive in March or April 2015. Dawn's observations of Vesta reveal a highly cratered surface, together with dark features that are believed to have originated in past impact events. Ceres is currently at opposition, and the present program aims to use deep WFC3 imaging to search for very low mass companions ("moons"), whose presence would be of significance in planning the details of the DAWN's final encounter.

GO 13626: Light Echoes and Environment of SN 2014J in M82

Image of the recent supernova in M82, Jan 24th (Katzman Automated Imaging Telescope/LOSS)

Type Ia supernovae are generally believed to be produced by the explosive deflagration of white dwarf star that exceeds the Chandrasekhar due to accretion from a binary companion, either a hydrogen-burning main-sequence/red giant star or another degenerate. Besides providing crucial information on stellar evolution and how stars enrich the interstellar medium, Type Ia supernovae have acquired global importance in recent years through their use as distance indicators. Indeed, these objects played a crucial role in identifying dark energy and the accelerating universe. In that context, it is important to understand the distribution of intrinsic properties of these exploding stars, and whether those properties, particularly lumunisuty, correlate with other parameters, such as metallicity. Relatively nearby supernovae that can be probed in detail are therefore crucial to the large mapping of the cosmic flow. Astronomers were therefore delighted with the discovery of a type Ia supernova in the relatively nearby starburst galaxy, M82 (d~3.5 Mpc). This object, designated SN2014J, was discovered on January 21st by a group of UCL undergraduates and their lecturer in a series of short exposures taken as a quick test as clouds closed in on London's Mill Hill Observatory. The supernoa reached maximum at V~10.5 in early February and has since declined to fainter than 14th magnitude at visual wavelengths. The current program aims to probe the immediate environments of the supernova by searching for evidence of light echoes - reflections of the original explosion produced by interstellar features in the vicinity of the supernova.