This week on HST

HST Programs: January 18, 2010 - January 24, 2010

Selected highlights

GO 11153: The Physical Nature and Age of Lyman Alpha Galaxies

Composite optical/X-ray/IR imaging of a high-redshift Lyman-alpha blob

Simple galaxy formation models envisage a period of extensive star formation at the earliest epochs. That activity is likely to be accompanied by substantial Lyman alpha emission, generated by ionising photons from short-lived, high-mass stars. The degree of such activity, however, and its duration remain matters of some conjecture, which can be addressed through deep, high resolution investigations of the underlying morphology of high-redshfit Lyman-alpha emitters. The higher angular resolution and increased sensitivity of HST offer significant advantages in characterising these systems. The present proposal is using HST to obtain follow-up F110W/F160W (J/H) images of 35 spectroscopically confirmed 4.5 < z < 6.5 Ly-alpha emitters. Initial observations were with NICMOS, and the progrma has moved to using WFC3 following SM4. These systems also have mid-IR data, taken using the IRAC camera on Spitzer. The observations will be used to fully characterise the spectral energy distributions and morphologies of these sources.

GO 11563: Galaxies at z~7-10 in the Reionization Epoch: Luminosity Functions to <0.2L* from Deep IR Imaging of the HUDF and HUDF05 Fields

The ACS optical/far-red image of the Hubble Ultra Deep Field

Galaxy evolution in the early Universe is a discipline of astronomy that has been transformed by observations with the Hubble Space Telescope. The original Hubble Deep Field, the product of 10 days observation in December 1995 of a single pointing of Wide Field Planetary Camera 2, demonstrated conclusively that galaxy formation was a far from passive process. The images revealed numerous blue disturbed and irregular systems, characteristic of star formation in galaxy collisions and mergers. Building on this initial progam, the Hubble Deep Field South (HDFS) provided matching data for a second southern field, allowing a first assessment of likely effects due to field to field cosmic variance, and the Hubble Ultra-Deep Field (UDF) probed to even fainter magitude with the Advanced Camera for Surveys (ACS). The highest redshift objects found in the UDF have redshifts approaching z~7. Pushing to larger distances, and greater ages, demands observatons at near-infrared wavelengths, as the characteristics signatures of star formation are driven further redward in the spectrum. The present program aims to extend observations beyond z~8 to z+9 or even 10 by using the WFC3-IR camera to obtain deep F850LP (Y), F105W (J) and F160W (H) images centred on the UDF and two flanking fields. Parallel observations with ACS will be used to extend the visible and red iamging data to even fainter magitudes. Analysis of the initial datasets has revealed 5 strong z~8 galaxy candidates within the UDF, and possible sources at even higher redshift.

GO 11572: Characterizing Atmospheric Sodium in the Transiting hot-Jupiter HD189733b

An artist's impression of the hot Jupiter circling a solar-type star

HD 198733 is a 7th magnitude G5 dwarf that lies at a distance of ~20 parsecs from the Sun, in the direction of the constellation of Vulpecula. Like many other nearby solar-type stars, HD 189733 has an associated planetary system, including a hot Jupiter, a ~1.15 MJ gas giant with an orbital period of 2.12 days. Most significantly, that inner planet transits the central star, making HD 189733 the closest transiting system found so far. Transiting systems offer a potential gold-mine for extrasolar planetary studies, since not only is the orbital inclination well defined, but the diameter (and hence the average density) is directly measureable form the eclipse depth, while the atmospheric composition can be probed through line absorption or re-radiated thermal flux. The results from these measurments can be used to test, and improve, theoretical models of extrasolar planets. These observations are best done from space (indeed, the only successful atmospheric observations to date have been with HST and Spitzer). HD 189733 has already been studied extensively with HST using the grism on the Advanced Camera for Surveys and, at near-infrared wavelengths, NICMOS. However, it's discovery postdated the STIS electronic failure, so it has never been studied at even moderate spectral resolution. The present observations will use the G750M grating on STIS to monitor three transits, and the data will be analysed for the presence of enhanced sodium absorption, as previously detected in the original bright transiting planet, HD 209458b.

GO 11839: The Cycles of Alpha Centauri

A wide-field view of Alpha and Beta Centauri

The Hubble Space Telescope is usually devoted to observing objects that are far below the detection limits of the human eye and, indeed, sometime too faint to be detected by any current ground-based observatory. However, space observations in general, and HST in particular, has another distinct advantage: sitting above the atmosphere gives access to wavelengths regions that are absorbed before they reach any ground-based aperture. Ultraviolet radiation is one of those key wavelength regions. Thus, HST will be using the STIS spectrograph to obtain high-resolution spectra of two of the Sun's nearest, and brightest, neighbours: Alpha Centauri A, a near twin of the Sun; and Alpha Centauri B, a slightly cooler and less massive early K-type dwarf. HST has observed both stars before, and the new observations will be resuming a campaign designed to monitor the stars' magnetic activity.