This week on HST

HST Programs: September 8 - September 14, 2014

Selected highlights

GO 12893: Study of Small and Cool Kepler Planet Candidates with High Resolution Imaging

The Kepler satellite

Kepler is a NASA Discovery-class mission, designed to search for extrasolar planets by using high-precision photometric observations to detect transits. Launched on 7 March 2009, Kepler continuously monitored ~100,000 (mainly) solar-type stare within a ~100 square degree region in Cygnus for more than 4 years. Routine observations ceased on May 11 2013 when a second reaction wheel failed; efforts are currently under way to examine the options for restoring observations. Regardless, the mission has been an astounding success. Ground-based observations have successfully detected a couple of dozen transiting planets (e.g. HD 209458); almost all are "hot jupiters", gas giants on short-period orbits which produce a photometric dip of ~10-2 with a period of a few days, with a smattering of neptune-sized "super-Earths". Kepler, in contrast, has identified more than 2,700 exoplanet candidates around over 2,000 candidate host stars. More significantly, the exquisite precision of Kepler's photometric observations enables it to detect the 0.01% transit signature of earth analogues in these systems. A subset of stellar binaries provide one of the main sources of confusion in searching for planetary transits, since "grazing" transits can mimic the planetary signature. This is particularly an issue with Kepler, since the optical system is designed to provide a broad psf, spreading the stellar flux over a large area on the detector to allow high photometric accuracy. As a result, faint eclipsing stellar binaries will contribute to the source counts. Moreover, since the target field is (intentionally) within the Milky Way, there is a significant potential for unresolved stars within the (relatively broad) Kepler psf to increase the total signal, and hence dilute the depth of transits, giving the appearance of a smaller diameter exoplanet. This program is using the high spatial resolution imaging provided by HST to study a subset of the Kepler Earth-like candidates to assess the potential of this effect.

GO 13331: Confirmation and characterization of young planetary companions hidden in the HST NICMOS archive

Archival HST NICMOS images of the planetary companions to HR 8799

Planet formation occurs in circumstellar disks around young stars. Most of the gaseous content of those disks dissipates in less than 10 million years, leaving dusty debris disks that are detectable through reflect light at near-infrared and, to a lesser extent, optical wavelengths. The structure of those disks is affected by massive bodies (i.e. planets and asteroids), which, through dynamical interactions and resonances, can produce rings and asymmetries. Analysis of the rangle of morphological structure in these systems provides insight into the distribution of properties of planetary systems; in a few cases, massive planetary companions can be detected directly. Ground-based instruments such as GPI and Sphere, mounted on Gemini and the VLT, are starting to have a significant impact on this subject, but the 2.4-metre HST remains a highly effective means of achieving the high-contrast required for the detection of both disks and candidate companions. To date, while many systems have been observed, only a relatively small number of systems have been imaged successfully at visual or near-infrared wavelengths. Archival HST imaging exists for many nearby stars, and a suite of new reduction techniques have been applied to those data, removing the direct starlight with greater fidelity to enable detection of faint debris disks. The present program builds on those results, using Wide-Field Camera 3 to obtain high-contrast images of six young stars that have been identified as having candidate planetary companions.

GO 13340: Detecting a Hot Companion to the Progenitor of the Type Ic Supernova 1994I in M51

WFPCC2 imaging of SN1994I in M51

Supernovae are the most spectacular form of stellar obituary. Since B2FH, the physical processes underlying their eruptive deaths have been known to play a key role in populating the ISM with metals beyond the iron peak. More recently, these celestial explosions have acquired even greater significance through the use of Type Ia supernovae as distance indicators in mapping the `dark energy' acceleration term of cosmic expansion. However, while there are well-established models for the two main types of supernovae (runaway fusion on the surface of a white dwarf in a binary system for Type Ia, or detonation of the core in Type II), the origins of the rarer Type Ib and Type Ic supernovae remain somewhat uncertain. Those supernovae are helium rich, and are believed to originate either from massive stars whose outer layers have been stripped through mass-loss, or from lower-mass stars in interacting binary systems where, again, the outer layers have been stripped to remove hydrogen from the system. In the latter case, the expectation is that the companion star to the supernova will survive the explosion and should be detectable as a hot supergiant. The present program aims to test this hypothesis through deep WFC3 imaging of the outer regions of M51, including the site of the Type Ic supernova, 1994I. That supernova was discovered by two amateur astronomers, Tim Puckett and Jerry Armstrong, on April 2 1994. Follow-up observations with the recently installed WFPC2 camera on HST provide accurate astrometry, and the new WFC3 data will be searched for a UV-bright source at that position.

GO 13517: 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.