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The Gradients in the 47 Tuc Red Giant Branch Bump and Horizontal Branch are Consistent with a Centrally Concentrated, Helium-enriched Second Stellar Generation
Nataf, D. M.; Gould, A.; Pinsonneault, M. H. +1 more
We combine ground- and space-based photometry of the Galactic globular cluster 47 Tuc to measure four independent lines of evidence for a helium gradient in the cluster, whereby stars in the cluster outskirts would have a lower initial helium abundance than stars in and near the cluster core. For our first and second lines of evidence, we show tha…
Probing the Faint End of the Quasar Luminosity Function at z~ 4 in the COSMOS Field
Murayama, T.; Taniguchi, Y.; Silverman, J. D. +16 more
We searched for quasars that are ~3 mag fainter than the SDSS quasars in the redshift range 3.7 <~ z <~ 4.7 in the COSMOS field to constrain the faint end of the quasar luminosity function (QLF). Using optical photometric data, we selected 31 quasar candidates with 22 < i' < 24 at z ~ 4. We obtained optical spectra for most of these ca…
Ultra-compact Dwarfs in the Coma Cluster
Peng, Eric W.; Chiboucas, Kristin; Tully, R. Brent +6 more
We have undertaken a spectroscopic search for ultra-compact dwarf galaxies (UCDs) in the dense core of the dynamically evolved, massive Coma cluster as part of the Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) Coma Cluster Treasury Survey. UCD candidates were initially chosen based on color, magnitude, degree of resolution within th…
Markarian 6: Shocking the Environment of an Intermediate Seyfert
Hardcastle, M. J.; Croston, J. H.; Kraft, R. P. +4 more
Markarian 6 is a nearby (D ~ 78 Mpc) Seyfert 1.5, early-type galaxy, with a double set of radio bubbles. The outer set spans ~7.5 kpc and is expanding into the halo regions of the host galaxy. We present an analysis of our new Chandra observation, together with archival XMM-Newton data, to look for evidence of emission from shocked gas around the …
The Progenitor Mass of SN 2011dh from Stellar Population Analysis
Dolphin, Andrew E.; Dalcanton, Julianne J.; Murphy, Jeremiah W. +2 more
Using Hubble Space Telescope photometry, we characterize the age of the stellar association in the vicinity of supernova (SN) 2011dh and use it to infer the zero-age main-sequence mass (M ZAMS) of the progenitor star. We find two distinct and significant star formation (SF) events with ages of <6 and 17+3 - 4 My…
Orbit-based Dynamical Models of the Sombrero Galaxy (NGC 4594)
Gebhardt, Karl; Richstone, Douglas; Kormendy, John +6 more
We present axisymmetric, orbit-based models to study the central black hole (BH), stellar mass-to-light ratio (M/L), and dark matter (DM) halo of NGC 4594 (M104, the Sombrero Galaxy). For stellar kinematics, we use published high-resolution kinematics of the central region taken with the Hubble Space Telescope, newly obtained Gemini long-slit spec…
Optical Polarization Mapping Toward the Interface Between the Local Cavity and Loop I
Santos, Fábio P.; Corradi, Wagner; Reis, Wilson
The Sun is located inside an extremely low density and quite irregular volume of the interstellar medium, known as the Local Cavity (LC). It has been widely believed that some kind of interaction could be occurring between the LC and Loop I, a nearby superbubble seen in the direction of the Galactic center. As a result of such interaction, a wall …
Uncovering Obscured Active Galactic Nuclei in Homogeneously Selected Samples of Seyfert 2 Galaxies
Ptak, A.; Sonnentrucker, P.; Heckman, T. M. +4 more
We have analyzed archival Chandra and XMM-Newton data for two nearly complete homogeneously selected samples of type 2 Seyfert galaxies (Sy2s). These samples were selected based on intrinsic active galactic nuclei (AGNs) flux proxies: a mid-infrared (MIR) sample from the original IRAS 12 µm survey and an optical ([O III]λ 5007 flux limited) …
Cosmic Origins Spectrograph Detection of Ne VIII Tracing Warm-Hot Gas Toward PKS 0405-123
Sembach, Kenneth R.; Savage, Blair D.; Shull, J. Michael +7 more
We report on the detection of Ne VIII in the Hubble Space Telescope/Cosmic Origins Spectrograph (COS) spectrum of the intervening absorption system at z = 0.495096 toward PKS 0405-123 (z em = 0.5726). The high signal-to-noise COS spectrum also covers absorption from H I, C III, O III, O IV, and O VI associated with this multiphase syste…
Hinode Observations Suggesting the Presence of a Local Small-scale Turbulent Dynamo
Lites, B. W.
Analysis of observations from the Hinode/Solar Optical Telescope spectropolarimeter (SP) yields results that are consistent with the operation of a small-scale turbulent dynamo in the upper solar convection zone. Examination of 45 Hinode data sets obtained in 2007 reveals only a very small correlation of the net polarity imbalance of the regions o…