This week on HST

HST Programs: March 14, 2011 - March 20, 2011

Selected highlights

GO 12099: Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey - SNe follow-up

High redshift supernovae from HST observations in previous cycles

CANDELS is one of three Multi-Cycle Treasury Program, whose observations will be executed over the next three HST Cycles. It builds on past investment of both space- and ground-based observational resources. In particular, it includes coverage of the two fields of the Great Observatory Origins Deep Survey (GOODS), centred on the northern Hubble Deep Field (HDF) in Ursa Major and the Chandra Deep Field-South in Fornax. In addition to deep HST data at optical and near-infrared wavelengths, the fields have been covered at X-ray wavelengths by Chandra (obviously) and XMM-Newton; at mid-infrared wavelengths with Spitzer; and ground-based imaging and spectroscopy using numerous telescopes, including the Kecks, Surbaru and the ESO VLT. This represents an accumulation of almost 1,000 orbits of HST time, and comparable scale allocations on Chandra, Spitzer and ground-based facilities. The CANDELS program is capitalising on this large investment, with new observations with WFC3 and ACS on both GOODS fields, and on three other fields within the COSMOS, EGS and UDS survey areas (see this link for more details). The prime aims of the program are twofold: reconstructing the history of galaxy formation, star formation and nuclear galactic activity at redshifts between z=8 and z=1.5; and searching for high-redshift supernovae to measure their properties at redshifts between z~1 and z~2. The program incorporates a tiered set of observations that complement, in areal coverage and depth, the deep UDF observations, while the timing of individual observations will be set to permit detection of high redshift SNe candidates, for subsequent separate follow-up. The present observations target a high-redshift supernova identified in the course of the survey imaging.

GO 12177: 3D-HST: A Spectroscopic Galaxy Evolution Treasury

Part of the GOODS/Chandra Deep Field South field, as imaged by HST

One of the exciting new capabilities offered by the post-SM4 Hubble Telescope is multi-object, low-resolution, near-infrared spectroscopy, using the two grisms available on the IR channel of Wide-Field Camera 3. These observations provide an important avenue for complementing wide-field imaging surveys. In particular, the present program aims to build on the extensive database currently being accumulated as part of the CANDELS Multi-Cycle Treasury program. CANDELS, itself, rests on past HST Treasury programs, and will provide multi-tiered imaging of five fields. 3D-HST will supplement portions of four fields (GOODS-south, AEGIS, the UDS and COSMOS fields) with WFC3/G141 and ACS/G800L grism data. The spectroscopic data will provide important additional information on the galaxy redshift distribution, and on the star formation characteristics in the redshift range 1 < z < 3.5. The data should also be useful in identifying quasars at high redshifts, potentially extending beyond z~6.

GO 12216: Taming the Invisible Monster with COS - Eclipse Spectroscopy of Epsilon Aurigae

Artist's impression of the dusty eclipsing system, Epsilon Aurigae

Epsilon Aurigae is one of the brighter stars in the constellation Auriga, the charioteer, lying close (south/preceeding) to the first magnitude star, Capella. Like many stars, Epsilon Aurigae is actually a binary (or even multiple) system; indeed, the orbital plane lies very close to the line of sight, leading to eclipses. The star is unusualy, however, in that the orbital period is 27.07 years, with each eclipse lasting approximately 2 years from first to last contact and the star fading by ~0.8 magnitudes in mid-eclipse. This long duration indicates that the "secondary" is substantially larger, and fainter, than one would expect, given the implied mass. The currently accepted model, proposed by Hoard et al (2010, ApJ 714, 549), postulates that the primary is a ~2.2 solar mass F-type post-AGB star, and the secondary is a ~5 solar mass B dwarf that still retains a substantial residual dusty disk, ~4 AU in diameter. The age is estimated as from 60 to 80 million years, and the implication is that the primary ejected ~4-5 solar masses during the AGB phase. The system entered its most recent eclipse in August 2009, and is expected to emerge sometime later this year. The present proposal aims to use COS to probe the nature of the secondary, search for diagnostics that can constrain the temperature and density of material along the line of sight, and probe the dusty disk.

GO 12311: Multiple Stellar Populations in Galactic Globular Clusters

NGC 2808, a globular cluster with multiple stellar populations

Globular clusters are remnants of the first substantial burst of star formation in the Milky Way. With typical masses of a few x 105 solar masses, distributed among several x 106 stars, the standard picture holds that these are simple systems, where all the stars formed in a single starburst and, as a consequence, have the same age and metallicity. Until recently, the only known exception to this rule was the cluster Omega Centauri, which is significantly more massive than most clusters and has both double main sequence and a range of metallicities among the evolved stars. Omega Cen has been joined by several additional clusters, including NGC 2808, which shows evidence for three distinct branches to the main sequence. The origin of this feature is remains uncertain, but it may be significant that NGC 2808 is also one of the more massive clusters, and might therefore be able to survive several burst of star formation (or, conversely, be the product of a multi proto-globular merger). Evidence for multiple populations has also been found in other clusters, including NGC 1851, 47 Tucanae and NGC 6752 - all relatively massive clusters. The present program aims to use high-precision UV (F275W) and far-red (F814W) WFC3 observations of those clusters, together with M4 and M22, to probe the detailed structure along the main sequence.