This week on HST

HST Programs: August 15, 2011 - August 21, 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 12221: The role of photoevaporation in clearing protoplanetary disks: mapping flows and determining mass flow rates

Artist's impression of the protoplanetary disk surrounding the nearby star, TW Hya

The T Tauri stage of evolution occurs early in a star's lifetime, within ~10 Myrs of its birth, when it still retains a dense, dust and gas-rich circumstellar disk. During this phase, there is substantial accretion of material onto the central star. This leads to heating of the inner regions of the accretion disk, and significant emission at ultraviolet and X-ray wavelengths. Previous HST programs (e.g. GO 10840 and GO 11616 ) have used STIS, the ACS/SBC and COS to investigate these processes at FUV and NUV wavelengths. The present program focuses on detailed spectroscopic investigations of two nearby T Tauri stars, TW Hya and T Cha. STIS is being used to map the distribution of the 6300 A forbidden oxygen line. This feature should provide a diagnostic for tracing the radial extent of gas evaporating from the disk, and provide a measure of the rate of photoevaporation. The observations will have a resolution close to ~6 AU, and the extent of the evaporative flows should provide constraints on whether the driving mechanism is extreme UV or X-ray radiation.

GO 12257: The Nature of Multiple Main Sequence Turn-offs and Dual Red Clumps in Magellanic Cloud Star Clusters

NGC 1818, a globular cluster in the Large Magellanic Cloud

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 Galactic clusters, including NGC 2808, NGC 1851 and 47 Tucanae. In addition, there is growing evidence for similarly complex stellar populations within at least some of the globular clusters associated with the Large and Small Magellanic Clouds. Several of the latter clusters show clear evidence for bimodality in the red clump stars, which lie towards the base of the red giant branch. The origin of this feature is remains uncertain, but it may be significant that the Galactic clusters are amongst the most massive within the Milky Way's population. The present program focuses on the Magellanic clusters, and will use WFC3 to obtain deep F475W (B-band) and F814W (I-band) imaging for a sample of 17 clusters.