This week on HST


HST Programs: February 3 - February 9, 2014

Program Number Principal Investigator Program Title
12880 Adam Riess, The Johns Hopkins University The Hubble Constant: Completing HST's Legacy with WFC3
13049 Tuan Do, University of Toronto Measuring the physical properties of the Milky Way nuclear star cluster with proper motions
13286 Ryan Foley, University of Illinois at Urbana - Champaign Understanding the Progenitor Systems, Explosion Mechanisms, and Cosmological Utility of Type Ia Supernovae
13310 Nicholas P. Abel, University of Cincinnati Main Campus The life and death of H2 in a UV-rich environment - Towards a better understanding of H2 excitation and destruction
13330 Bradley M Peterson, The Ohio State University Mapping the AGN Broad Line Region by Reverberation
13335 Adam Riess, The Johns Hopkins University HST and Gaia, Light and Distance
13344 Adam Riess, The Johns Hopkins University A 1% Measurement of the Distance Scale with Perpendicular Spatial Scanning
13362 Amy Bonsor, Institut de Planetologie et d'Astrophysique de Grenoble Constraining the structure of the Kappa Cr B planetary system, a unique subgiant, orbited by two companions and a debris disc
13364 Daniela Calzetti, University of Massachusetts - Amherst LEGUS: Legacy ExtraGalactic UV Survey
13379 Antonino Paolo Milone, Australian National University Multiple stellar populations in the young Large Magellanic Cloud cluster NGC1856
13408 Jon Mauerhan, University of California - Berkeley Constraining the Physical Properties of LBV Nebulae in the Galactic Center Environment
13417 David P. Bennett, University of Notre Dame Measuring the Exoplanet Mass Function Beyond the Snow-Line
13449 Marla C. Geha, Yale University A Non-Universal Initial Mass Function in the Ultra-Faint Galaxy Coma Berenices
13459 Tommaso L. Treu, University of California - Santa Barbara The Grism Lens-Amplified Survey from Space {GLASS}
13463 Kailash C. Sahu, Space Telescope Science Institute Detecting and Measuring the Masses of Isolated Black Holes and Neutron Stars through Astrometric Microlensing
13467 Jacob L. Bean, University of Chicago Follow The Water: The Ultimate WFC3 Exoplanet Atmosphere Survey
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
13496 Jennifer Lotz, Space Telescope Science Institute HST Frontier Fields - Observations of MACSJ0416.1-2403
13621 Ariel Goobar, Stockholm University The closest reddened Type Ia supernova in the HST life time
13623 Zolt Levay, Space Telescope Science Institute Hubble Heritage observations of NGC 2174 for HST 24th anniversary

Selected highlights

GO 12880: The Hubble Constant: Completing HST's Legacy with WFC3


NGC 7541 (upper left), one of the spiral galaxies targeted in this program
The Hubble constant remains a key parameter in understanding cosmology and the evolution of the Universe. Refining measurements of H0 therefore still represents a vital means of probing the nature of dark energy. The present program aims to tackle this question by laying a firmer foundation to the SNe Ia distance scale. The WFC3 IR camera will be used to identify and characterise Cepheid variables in eight relatively nearby galaxies that have hosted Type Ia SNe. Cepheids have signficantly lower amplitude at near-infrared wavelengths, and the measured magnitudes are less subject to uncertainties due to foreground reddening and variations in metallicity. As a consequence, determining the mean apparent magnitude, and hence the period/apparent magnitude relation, is substantially more straightforward than at optical wavelengths. WFC3 has revolutionised this field by providing substantial greater areal coverage and higher precision photometry than NICMOS. Past observational program have targeted the Cepheids in the maser galaxy, NGC 4258, as well as Galactic Cepheids. The present program targets eight galaxies that have hosted Type Ia supernovae, offering the prospect of tying the SNe Ia scale directly to the Galaxy and to NGC 4258, avoiding the many intermediate steps of previous analyses. The aim is to reduce the level of systematics in determinations of H0 to the 1-2 percent level, setting signficantly stronger constraints on dark energy.

GO 13330: Mapping the AGN Broad Line Region by Reverberation


Simulations of the appearance and velocity structure within an AGN disk (see Keith Horne's web page).
Active galaxies (AGNs) are generally luminous systems, characterised by the presence of strong nuclear emission lines of numerous species including H, He I, He II, and Fe, Ca, O, C and S over a range of ionisations. These features originate from gas clouds in the nuclear regions, with the energy supplied through accretion onto a central massive black hole. The high-temperature, rapidly-rotating gas clouds nearest the central engine are responsible for producing broad emission lines (hence, the "Broad Line Region"). The structure of the BLR can be discerned using a technique known as reverberation mapping: variations in the accretion rate lead to fluctuations in luminosity; those variations lead, in turn, to variations in the photoionisation of the BLR, and corresponding changes in spectral line strengths and velocities; monitoring those changes, and correlating them with the photometric variability of the central source, measures the light travel time from nucleus to BLR gas, and hence maps the size of the BLR. The present prorgam will use the Cosmic Origins Spectrograph to undertake systematic monitoring of the nuclear regions of the Seyfert I galaxy, NGC 5548. The observatons are spread over the next 6 months, with one orbit per day for 179 days.

GO 13364: LEGUS: Legacy ExtraGalactic UV Survey


UGC 4305 = Holmberg II - Arp 268, one of the star-forming galaxies targeted by LEGUS
Understanding the global architecture of star formation is a key step towards understanding the morphological evolution of galaxies and the characteristics of the underlying stellar populations. HST has devoted extensive resources to observations of nearby galaxies over its lifetime, including detailed surveys of a handful of systems, notably the PHAT survey of M31, with the enhanced imaging capabilities made available following SM4. Most of those programs, however, have focused on optical, far-red and, to a lesser extent, near-infrared wavelengths. While those observations provide high-quality colour-magnitude data that enable an exploration of relatively mature populations, they are less effective at probing active star-formation sites populated by young, high-mass stars. Those regions are most prominent at ultraviolet wavelengths, and the present program aims to capitalise on the past heritage of HST observations vby adding near-UV imaging for 50 nearby galaxies. The 50 targets are drawn from a catalogue of 400 systems within ~11 Mpc of the Milky Way, and have been selected to provide a fair sampling of the wide variety of galactic systems within that volume. The program will image star-forming regions in these systems in near-UV and blue wavelengths using the WFC3 UVIS channel with the F275W, F336W and F438W filters, supplemented by F55W and F81wW (V and IK) where necessary.

GO 13467: Follow The Water: The Ultimate WFC3 Exoplanet Atmosphere Survey


Probing the atmosphere of a transiting exoplanet
The first exoplanet, 51 Peg b, was discovered in 1995 through high-precision radial velocity measurements. 51 Pegb was followed by a trickle, and then a flood of other discoveries, as astronomers realised that there were other solar systems radically different from our own, where "hot jupiters" led to short-period, high-amplitude velocity variations. Then, in 1999, came the inevitable discovery that one of those hot jupiters. HD 209458b, was in an orbit aligned with our line of sight to the star, resulting in transits. Since that date, the number of known transiting exoplanet systems has grown to more than 400 in over 300 planetary systems, with the overwhelming majority identified by the Kepler satellite, which has also contributed close to 3,000 additional (very strong) candidates. As these observations have accumulated,the broad diversity of exoplanet systems has become increasingly apparent. Transiting systems are invaluable, since they provide not only unambiguous measurements of mass and diameter, but also an opportunity to probe the atmospheric structure by differencing spectra taken during and between primary secondary transit. Such observations are best done from space: indeed, while high-precision ground-based observations have succeeded in constraining atmospheric properties in a few systems, the only successful detections of atmospheric features to date have been with HST and Spitzer. HST capabilities have been enhanced in the last few years with addition of spatial scanning, moving the target star over the chip in a controlled fashion during an observation. This allows observers to accumulate images or spectra of substantially higher signal-to-noise, a crucial advantage if one is looking for flux differences of elss than 1 part in 104. Past programs have accumulated observations of over a dozen exoplanets, using STIS at optical wavelengths and WFC3 in the near-infrared. The present program targets eight exoplanet systems with a diverse range of properties: HD 209458b,GL 3470b, HAT-P-26b, WASP-12b, WASP-18b, WASP-43b, WASP-80b and WASP-19b. The WFC3-IR G141 grism will be used to search for the characteristic near-infrared spectral features due to water in the amospheres of these exoplanets.

Past weeks:
page by Neill Reid, updated 28/1/2014
These pages are produced and updated on a best effort basis. Consequently, there may be periods when significant lags develop. we apologise in advance for any inconvenience to the reader.