Search Publications
X-Ray and Optical Observations of the Unique Binary System HD 49798/RX J0648.0-4418
Tiengo, A.; Mereghetti, S.; Stella, L. +5 more
We report the results of XMM-Newton observations of HD 49798/RX J0648.0-4418, the only known X-ray binary consisting of a hot sub-dwarf and a white dwarf. The white dwarf rotates very rapidly (P = 13.2 s) and has a dynamically measured mass of 1.28 ± 0.05 M sun. Its X-ray emission consists of a strongly pulsed, soft component, well fit …
2011 February 15: Sunquakes Produced by Flux Rope Eruption
Green, L. M.; Zharkova, V. V.; Matthews, S. A. +1 more
We present an analysis of the 2011 February 15 X-class solar flare, previously reported to produce the first sunquake in solar cycle 24. Using acoustic holography, we confirm the first, and report a second, weaker, seismic source associated with this flare. We find that the two sources are located at either end of a sigmoid, which indicates the pr…
A 205 µm [N II] Map of the Carina Nebula
Stark, A. A.; Stacey, G. J.; Kamenetzky, J. +5 more
We present the results of a ~250 arcmin2 mapping of the 205 µm [N II] fine-structure emission over the northern Carina Nebula, including the Car I and Car II H II regions. Spectra were obtained using the South Pole Imaging Fabry-Perot Interferometer (SPIFI) at the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) a…
A Correlation Between Host Star Activity and Planet Mass for Close-in Extrasolar Planets?
Schmitt, J. H. M. M.; Poppenhaeger, K.
The activity levels of stars are influenced by several stellar properties, such as stellar rotation, spectral type, and the presence of stellar companions. Analogous to binaries, planetary companions are also thought to be able to cause higher activity levels in their host stars, although at lower levels. Especially in X-rays, such influences are …
The Circumstellar Environment of R Coronae Borealis: White Dwarf Merger or Final-helium-shell Flash?
Ivison, R. J.; Olofsson, G.; Bond, Howard E. +21 more
In 2007, R Coronae Borealis (R CrB) went into a historically deep and long decline. In this state, the dust acts like a natural coronagraph at visible wavelengths, allowing faint nebulosity around the star to be seen. Imaging has been obtained from 0.5 to 500 µm with Gemini/GMOS, Hubble Space Telescope/WFPC2, Spitzer/MIPS, and Herschel/SPIRE…
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…