This week on HST

HST Programs: February 5 - February 11, 2007

HST has resumed science observations with NICMOS, FGS and WFPC2.

Some selected highlights

GO 10792: Quasars at Redshift z=6 and Early Star Formation History

SDSS 1030+0524, one of the high redshift QSOs targeted in this program

One of the major achievements of the Sloan Digital Sky Survey has been the detection of numerous high redsift quasars. These high luminosity objects serve as cosmic lamp-posts when it comes to probing star formation at such early epochs (lookback times exceeding 10 Gyrs): quasars are powered by accretion onto black holes, which are likely to form in high-mass (proto-)galaxies; those galaxies, in turn, are likely to be in high density environments (i.e. proto-clusters); thus, detailed investigations of the properties of high-redshift QSOs is likely to provide a snapshot of galaxy structure at thse early epochs. The present proposal concentrates on z>6 QSOs, using the NICMO grisms to obtain low resolution near-IR spectra that will allow measurement of the relative abundance of Fe and Mg in those objects. Magnesium is an alpha element, generated predominantly in Type II SN; Fe comes predominantly from Type I SN, which require 0.5-1 Gyrs to reach fruition; hence, this ratio provides an estimate of the time that has elapsed since the first outburst of star formation in these systems.

GO 10860: The largest Kuiper Belt Objects

The view from sedna: an artist's impression

The Kuiper Belt lies beyond the orbit of Neptune, extending from ~30 AU to ~50 AU from the Sun, and includes at least 70,000 objects with diameters exceeding 100 km. Setting aside Pluto, the first trans-Neptunian objects were discovered in the early 1990s. Most are relatively modest in size, with diameters of a few hundred km and photometric properties that suggested an icy composition, similar to Pluto and its main satellite, Charon. Over the last three years, however, a handful of substantially larger bodies have been discovered, with diameters of more than 1000 km; one of the objects, 2003 UB313, is comparable in size to Pluto (2320 km.). These recent results, of course, were one of the main stimuli for the IAU's recent revision of Pluto's status from planet to `dwarf planet' - an issue that still remains contentious in some quarters. However, regardless of spats over nomenclature, it is clear that these objects (ice planets?) are a significant component in the outer Solar System. Both HST and the Spitzer infrared space telescope have played an important role in these recent investigations, measuring the angular diameter of the larger KBOs, and the albedo over a wide range of wavelengths. The aim of the present set of observations is to target ~20 trans-Neptunian objects, using red (F606W) images and low-resolution spectra, obtained with the High Resolution Camera on the Advanced Camera for Surveys, to probe their size and chemical composition.

GO 10862: Comprehensive Auroral Imaging of Jupiter and Saturn during the International Heliophysical Year

HST imaging of aurorae near Saturn's poles

2007 has been designated the International Heliophysical Year, and HST will be playing a key part in the associated scientific activities by participating in a detailed investigation of auroral activity in jupiter and Saturn. Planetary aurorae are stimulated by the influx of charged particles from the Sun, which travel along magnetic field lines and funnel into the atmosphere near the magnetic poles. Aurorae therefore require that a planet has both a substantial atmosphere and a magnetic field. They are a common phenomenon on Earth, sometimes visible at magnetic latitudes more than 40 degrees from the pole, and have also been seen on Jupiter, Saturn, Uranus and Neptune. Jovian auroral activity is also affected by the Galilean satellites, which generate electric currents that can produce bright auroral spots, and, in some cases, have their own auroral storms. HST will use the ACS Solar Blind Channel to monitor activity on the two largest gas giants. The initial campaign, starting in early January, focuses on Saturn, which is at opposition. In February, the New Horizons spacecraft will fly by Jupiter, using the strong gravitational field to propel it on its way to Pluto. During the fly-by, New Horizons will carry out a number of experiments ( see this link ) Finally, Jupiter will be surveyed while it is at opposition in June 2007.