Search Publications
Mass-radius relations for white dwarf stars of different internal compositions
Althaus, L. G.; Panei, J. A.; Benvenuto, O. G.
The purpose of this work is to present accurate and detailed mass-radius relations for white dwarf (WD) models with helium, carbon, oxygen, silicon and iron cores, and with and without a hydrogen envelope, by using a fully updated stellar evolutionary code. We considered masses from 0.15 Msun to 0.5 Msun for the case of hel…
Membership and Multiplicity among Very Low Mass Stars and Brown Dwarfs in the Pleiades Cluster
Zapatero Osorio, M. R.; Luhman, K. L.; Martín, E. L. +5 more
We present near-infrared photometry and optical spectroscopy of very low mass stars and brown dwarf candidates in the Pleiades open cluster. The membership status of these objects is assessed using color-magnitude diagrams, lithium and spectral types. Eight objects out of 45 appear to be nonmembers. A search for companions among 34 very low mass P…
Chandra Observations of the X-Ray Narrow-Line Region in NGC 4151
Marshall, H. L.; Lee, J. C.; Ogle, P. M. +1 more
We present the first high-resolution X-ray spectrum of the Seyfert 1.5 galaxy NGC 4151. Observations with the Chandra High-Energy Transmission Grating Spectrometer reveal a spectrum dominated by narrow emission lines from a spatially resolved (1.6 kpc), highly ionized nebula. The X-ray narrow-line region is composite, consisting of both photoioniz…
The Photospheric Convection Spectrum
Raymond, J.; Hathaway, D. H.; Bogart, R. S. +5 more
Spectra of the cellular photospheric flows are determined from observations acquired by the MDI instrument on the SOHO spacecraft. Spherical harmonic spectra are obtained from the full-disk observations. Fourier spectra are obtained from the high-resolution observations. The p-mode oscillation signal and instrumental artifacts are reduced by tempo…
How Much Do Helioseismological Inferences Depend on the Assumed Reference Model?
Basu, Sarbani; Pinsonneault, M. H.; Bahcall, John N.
We investigate systematic uncertainties in determining the profiles of the solar sound speed, density, and adiabatic index using helioseismological techniques. We find that rms uncertainties (averaged over the Sun) of ~0.02%-0.04% are contributed to the sound-speed profile by each of three sources: (1) the choice of assumed reference model, (2) th…
The Hubble Deep Fields
Dickinson, Mark; Ferguson, Henry C.; Williams, Robert
The Hubble space telescope observations of the northern Hubble deep field, and more recently its counterpart in the south, provide detections and photometry for stars and field galaxies to the faintest levels currently achievable, reaching magnitudes V ~ 30. Since 1995, the northern Hubble deep field has been the focus of deep surveys at nearly al…
Low- and High-Ionization Absorption Properties of Mg II Absorption-selected Galaxies at Intermediate Redshifts. I. General Properties
Charlton, Jane C.; Schneider, Donald P.; Steidel, Charles C. +4 more
We present extensive metal-line absorption properties for 45 absorption systems that were selected by their Mg II absorption at redshifts between 0.4 and 1.4. For each system the properties of several chemical species are determined, including a wide range of ionization conditions. In the optical, the absorption systems have been observed at ~6 km…
A Candidate Substellar Companion to HR 7329
Weinberger, Alycia J.; Schneider, Glenn; Hines, Dean C. +10 more
We present the discovery of a candidate substellar companion from a survey of nearby young stars made with the Near-Infrared Camera and Multiobject Spectrometer coronagraph on the Hubble Space Telescope. The H~12 mag object was discovered approximately 4" from the young A0 V star HR 7329. Using follow-up spectroscopy from the Space Telescope Imagi…
An Excess of Submillimeter Sources near 4C 41.17: A Candidate Protocluster at Z = 3.8?
Ivison, R. J.; Smail, Ian; Dunlop, J. S. +3 more
Biased galaxy-formation theories predict that massive galaxies at high redshifts should act as signposts to high-density environments in the early universe, which subsequently evolve into the cores of the richest clusters seen at the present day. These regions are characterized by overdensities of young galaxies, perhaps including a population of …
STIS Coronagraphic Imaging of the Herbig AE Star: HD 163296
Kimble, R.; Linsky, J. L.; Bruhweiler, F. C. +7 more
Coronagraphic imaging with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope reveals a ~450 AU radius circumstellar disk around the Herbig Ae star HD 163296. A broadband (0.2-1.0 µm) reflected light image shows the disk oriented at a position angle of 140deg+/-5deg and inclined to our line of …