This week on HST

HST Programs: December 19, 2011 - December 25, 2011

Selected highlights

GO 12060/12062: CANDELS: Galaxy Assembly and the Evolution of Structure over the First Third of Cosmic Time

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

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 follow-up. The present set of observations is part of the GOODS (South) deep field survey.

GO 12291: STIS Coronagraphy of Spitzer-selected Debris Disks

HST image of the face-on debris disk in the G2 dwarf, HD 107146

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. HST currently provides the only means of achieving the high-contrast required for the detection of scattered light from these disks in the presence of the bright parent stars. 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. The present program aims to expand the sample by targetting ten systems that are known to have circumstellar disks based on Spitzer observations, and which are likely to be sufficiently bright to be detected by HST. The present proposal will use the occulting bar on the Space Telescope Imaging Spectrograph to carry out coronagraphic imaging at visual wavelengths.

GO 12463: Target of Opportunity Imaging of an Unusual Cloud Feature on Uranus

HST images of a bright spot that appeared on Uranus in 2005

The atmospheres of the gas giant planets in the solar system are dynamic entities that can exhibit dramatic changes over a variety of timescales. Those changes are most apparent in Jovian atmosphere, which displays a wide variety of bands and spots, reflecting complex meteorological phenomena (see, e.g., previous ACS observations of the upper atmosphere and of the new little red spot ). This is not surprising since Jupiter atmosphere receives the highest input of solar energy. However, secular variations are also evident in the atmospheres of the outer planets, albeit usually at a more subtle level. The present program aims to monitor atmospheric changes in Uranus. Both Uranus and its companion ice-giant, Neptune, exhibit long-term seasonal variations whose origins are not yet well understood; both are capable of generating both dark and bright spots - phenomena that are presumably related to Jupiter's Great Red Spot and Saturn's Great White Spot. Bright spots were first identified on Uranus shortly after the turn of the century, as the planet was reaching equinox, when the equator is aligned with the solar direction. The current hypothesis is that the increased inslation is leading to the formation of storms within the atmosphere that, on rare occasion, generate giant anvil clouds that extend above the normal cloud layer, and become visible as bright spots. The present event was identified in near-infrared images taken by the Gemini North telescope in late October. Wide Field camera 3 will be used to obtain images in a range of UV/optical narrow-band filters to probe the more detailed nature of the current eruption,

GO 12592: Understanding the Progenitor Systems, Explosion Mechanisms, and Cosmological Utility of Type Ia Supernovae

Supernovae in the nearby galaxy, NGC 2770

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), some significant uncertainties remain concerning the physical details of the disruption, and, potentially, the overall uniformity of these events. Consequently, there is potential for systematic bias in the distance estimates. The present program aims to address this issue through detailed observations of a small number of relatively nearby Type Ia Sne, using the Space telescope Imagign Spectrograph to provide spectral coverage over the full UV and visual wavelength ergime. The program aims to pick up the supernovae before maximum, and take spectra at regular (~4 day) intervals, providing detailed coverage of the changing abundances within the SNe ejecta. This is a target of opportunity, and the present set of observations are aimed at SN 2011iv in NGC 1404, an elliptical galaxy lying at a distance of ~19 Mpc within the Fornax cluster. The supernova was discovered at 13th magnitude by amateur astronomer Stuart Parker on December 2nd. The first HST observations were made on December 11th, with subsequent observations on the 15th and 20th, and planned observations for Christmas Eve, Dec 28th, New Year's day and around January 9th.