This week on HST


HST Programs: June 16 - June 22, 2014

Program Number Principal Investigator Program Title
12884 Harald Ebeling, University of Hawaii A Snapshot Survey of The Most Massive Clusters of Galaxies
12903 Luis C. Ho, Carnegie Institution of Washington The Evolutionary Link Between Type 2 and Type 1 Quasars
13007 Lee Armus, California Institute of Technology UV Imaging of Luminous Infrared Galaxies in the GOALS Sample
13046 Robert P. Kirshner, Harvard University RAISIN: Tracers of cosmic expansion with SN IA in the IR
13302 J. Michael Shull, University of Colorado at Boulder COS Spectra of High-Redshift AGN: Probing Deep into the Rest-Frame Ionizing Continuum and Broad Emission Lines
13305 Carolin Villforth, University of St. Andrews Do mergers matter? Testing AGN triggering mechanisms from Seyferts to Quasars
13330 Bradley M Peterson, The Ohio State University Mapping the AGN Broad Line Region by Reverberation
13341 Schuyler D. Van Dyk, California Institute of Technology The Stellar Origins of Supernovae
13346 Thomas R. Ayres, University of Colorado at Boulder Advanced Spectral Library II: Hot Stars
13347 Joel N. Bregman, University of Michigan The Missing Baryons Around Nearby Dwarf Galaxies
13405 Robert P. Kirshner, Harvard University SAINTS: Images of SN 1987A
13412 Tim Schrabback, Universitat Bonn, Argelander Institute for Astronomy An ACS Snapshot Survey of the Most Massive Distant Galaxy Clusters in the South Pole Telescope Sunyaev-Zel'dovich Survey
13423 Ryan J. Cooke, University of California - Santa Cruz Primordial lithium in z~0, metal-poor damped Lyman alpha systems
13435 Matteo Monelli, Instituto de Astrofisica de Canarias Multiple populations in external globular glusters: the Fornax dSph, the LMC, and the SMC
13472 Wendy L. Freedman, Carnegie Institution of Washington The Hubble Constant to 1%? STAGE 4: Calibrating the RR Lyrae PL relation at H-Band using HST and Gaia Parallax Stars
13480 Andrew J. Levan, The University of Warwick Super-luminous supernovae without host galaxies
13495 Jennifer Lotz, Space Telescope Science Institute HST Frontier Fields - Observations of Abell 2744
13633 John R. Spencer, Southwest Research Institute A Kuiper Belt Object for the New Horizons Mission

Selected highlights

GO 12903: The Evolutionary Link Between Type 2 and Type 1 Quasars


Artist's impression of the black hole and surrounding torus in an AGN
This year (2013) is the fiftieth anniversary of the recognition that QSOs (quasars, quasi-stellar objects) were extremely luminous objects lying at substantial redshifts. The central engine powering these luminous objects is now recognised as a supermassive black hole, marking the central regions of a galaxy. As such, QSOs are clearly related to (and more luminous than) active galactic nuclei (AGN). Like AGNs, QSOs have been segregated into two categories based on their spectral properties: systems with broad lines are characterised as Type 1 QSOs; systems with narrow lines are classed as Type 2. As with AGN, the underlying cause of these differences is generally believed to reside more in our perspective than on the sources themselves: heavily obscured systems, where the central accretion disk lies behind a thick veil of dust, are observed as Type 2 systems; they are expected to evolve to form Type 1 systems as the dust is ablated and destroyed. The present SNAP program aims to test this scenario by coupling mid-infrared Herschel observations, probing the dust environment, with HST near-infrared WFC3 imaging of targets drawn from two matched samples of Type 1 and Type 2 QSOs.

GO 13405: SAINTS - Images of SN 1987A

November 2003 HST image of the SN1987A gaseous ring SN1987A, in the Large Magellanic Cloud, is (as far as we know) the nearest supernova to the Sun since Kepler's supernova of 1604. While its eruption, in January 1987, predated HST's launch by over 3 years, the remnant has been a regular observational target since the installation of COSTAR at the first servicing mission. Those high resolution observations have revealed the development, and evolution, of extensive, intricate structures as the blast wave from SN1987A encounters the surrounding interstellar medium. In particular, a striking circum-remnant ring has developed, with numerous hot spots stimulated by the fastest moving debris. The present HST program both the UVIS and IR channels on WFC3 to continue monitoring the development of those features, using a series of observations that are co-ordinated with the Chandra X-ray Observatory. Over the past few cycles, the hotspots are fusing as the shock fully enters the ring, and photons from these regions are exciting previously hidden gas outside the ring, illuminating mass lost from the progenitor before the explosion. The inner debris are now well resolved, and clearly aspherical. Overall, these observations provide crucial insight into the earliest stages of formation of a supernova remnant.

GO 13472: The Hubble Constant to 1%? STAGE 4: Calibrating the RR Lyrae PL relation at H-Band using HST and Gaia Parallax Stars

RR Lyrae's light curve at visible wavelengths
The classical cosmic distance scale rests on a series of distance indicators that step outwards from the Milky Way, establishing reliable measurements to ever more distant galaxies. Cephids have long been the prime calibrators in this process, but other pulsating variables, notably Mira AGB long-period variables and RR Lyrae variables, also make significant contributions. RR Lyrae variables are evolved, near-solar-mass stars that are passing through the instability strip where it crosses the horizontal branch. With periods of 0.5 to 1.5 days, they have long served as distance indicators for old stellar populations (Baade's Population II). They have been known in the Galactic field and in Galactic globular clusters for over 150 years, and they are also present in the older stellar populations of the dwarf spheroidal Galactic satellites. Cluster (or dsph) RR Lyraes are particularly interesting, since their metallicities and ages can be deduced from analysis of the colour-magnitude diagrams for those systems. They are significantly less luminous than Cepheids, nonetheless, near-infrared photometric monitoring has demonstrated that these stars delineate a period-luminosity relation at those wavelengths that has the potential to establish distances to better than 1.5% accuracy. The absoltue calibration of that relationship, however, rests on only 4 nearby RR Lyraes with trigonometric parallax measurements. The present program aims to add to the sample of astrometricall well-observed RR Lyraes by using spatial scanning on WFC3 to determine accurate parallaxes for a sample of Galactic variables lying at distances up to several kpc from the Sun. Spatial scanning enables astrometry to an acuracy of ~40 microarcseconds, offering the prospect of distances accurate to 4% for individual stars, and an overall distance scale calibration accurate to better than 3%%.

GO 13633: A Kuiper Belt Object for the New Horizons Mission


Hubble Space Telescope images of the Pluto system, including the recently discovered moons, P4 and P5
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 suggest an icy composition, similar to Pluto and its main satellite, Charon. In recent years, a handful of substantially larger bodies have been discovered, with diameters of more than 1000 km; indeed, one object, Eris (2003 UB13), is slightly larger than Pluto (2320 km) and 25% more massive. We know the mass for Eris because it has a much lower mass companion, Dysnomia, which orbits Eris with a period of 16 days (see this recent press release ). Pluto itself has at least 5 companions: Charon, which is about 1/7th the mass of Pluto, and the much smaller bodies, Hydra, Nix, P4 and P5 discovered through HST observations within the last few years. The New Horizons Mission was launched on January 19th 2006 with the prime purpose of providing the first detailed examination of Pluto, one of the largest members of the Kuiper Belt and, until recently, the outermost planet in the solar system. The Pluto encounter represents the first phase of the originally-proposed mission. Following the fly-by, set for Bastille day in 2015, the aim is to direct New Horizons towards one or more smaller members of the Kuiper Belt, with the goal of providing a closer look at these icy bodies. However, New Horizons needs to identify an appropriate target - a KBO with orbital parameters such that New Horizons can use its modest complement of remaining fuel to reach the target. Adding a further complication, Pluto happens to lie within 5 degrees of the Galactic Plane and the consequent high star density has proven a barrier to deep ground-based searches. As a consequence, the New Horizons team has applied for, and received, Hubble time to search an area roughly the size of the full moon to try to identify a suitable target. The present observations represent part of a pilot program; if that program succeeds in detecting at least 2 cold, classical KBOs, the main survey will be triggered and, with luck, a new destination for New Horizons located.
Past weeks:
page by Neill Reid, updated 19/6/2014
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