Search Publications
Chandra Observations of ``The Antennae'' Galaxies (NGC 4038/9)
Zezas, A.; Fabbiano, G.; Murray, S. S.
We report the results of a deep Chandra ACIS pointing at the merging system NGC 4038/9. We detect an extraordinarily luminous population of X-ray sources, with luminosity well above that of XRBs in M31 and the Milky Way. If these sources are unbeamed XRBs, our observations may point to them being 10-(a few)100 Msolar black hole counterp…
Investigation of Mass Flows beneath a Sunspot by Time-Distance Helioseismology
Zhao, Junwei; Kosovichev, Alexander G.; Duvall, Thomas L., Jr.
A time-distance helioseismic technique is employed to analyze a set of high-resolution Dopplergram observations of a large sunspot by SOHO/MDI on 1998 June 18. A regularized, damped least-squares inversion is applied to the measurements of travel times to infer mass flows around the sunspot below the solar surface. Powerful converging and downward…
Nuclear Luminosities and Radio Loudness of Seyfert Nuclei
Ho, Luis C.; Peng, Chien Y.
Historically, Seyfert nuclei have been considered to be radio-quiet active galactic nuclei (AGNs). We question this widely held assumption by showing that the distribution of the radio-to-optical luminosity ratio, R≡Lν(6 cm)/Lν(B), when properly measured for the nuclear component, places the majority of type 1 Seyfert nuclei …
Isocam-Cvf 5-12 Micron Spectroscopy of Ultraluminous Infrared Galaxies
Lutz, D.; Genzel, R.; Sturm, E. +10 more
We present low-resolution mid-infrared (MIR) spectra of 16 ultraluminous infrared galaxies (ULIRGs) obtained with the circular variable filter (CVF) spectroscopy mode of ISOCAM on board the Infrared Space Observatory (ISO). Our sample completes previous ISO spectroscopy of ultra- and hyperluminous infrared galaxies toward higher luminosities. The …
A New Measurement of the Primordial Abundance of Deuterium: Toward Convergence with the Baryon Density from the Cosmic Microwave Background?
Bowen, David V.; Pettini, Max
From the analysis of the near-UV spectrum of the quasar (QSO)2206-199, obtained with a long series of exposures with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, we deduce a value D/H=(1.65+/-0.35)×10-5 (1 σ error) for the abundance of deuterium in the zabs=2.0762 damped Lyα system (DLA) along this …
H2 and CO Emission from Disks around T Tauri and Herbig Ae Pre-Main-Sequence Stars and from Debris Disks around Young Stars: Warm and Cold Circumstellar Gas
Thi, W. F.; Natta, A.; van Dishoeck, E. F. +8 more
We present ISO Short-Wavelength Spectrometer observations of H2 pure-rotational line emission from the disks around low- and intermediate-mass pre-main-sequence stars as well as from young stars thought to be surrounded by debris disks. The pre-main-sequence sources have been selected to be isolated from molecular clouds and to have cir…
The Nuclear and Circumnuclear Stellar Population in Seyfert 2 Galaxies: Implications for the Starburst-Active Galactic Nucleus Connection
Heckman, Timothy; Leitherer, Claus; González Delgado, Rosa M.
We report the results of a spectroscopic investigation of a sample of 20 of the brightest type 2 Seyfert nuclei. Our goal is to search for the direct spectroscopic signature of massive stars and thereby probe the role of circumnuclear starbursts in the Seyfert phenomenon. The method used is based on the detection of the higher order Balmer lines a…
Flash Mixing on the White Dwarf Cooling Curve: Understanding Hot Horizontal Branch Anomalies in NGC 2808
Brown, Thomas M.; Hubeny, Ivan; Sweigart, Allen V. +2 more
We present an ultraviolet color-magnitude diagram (CMD) spanning the hot horizontal branch (HB), blue straggler, and white dwarf populations of the globular cluster NGC 2808. These data were obtained with the far-UV and near-UV cameras on the Space Telescope Imaging Spectrograph (STIS). Although previous optical CMDs of NGC 2808 show a high-temper…
Theory of Extrasolar Giant Planet Transits
Hubbard, W. B.; Fortney, J. J.; Lunine, J. I. +3 more
We present a synthesis of physical effects influencing the observed light curve of an extrasolar giant planet (EGP) transiting its host star. The synthesis includes a treatment of Rayleigh scattering, cloud scattering, refraction, and molecular absorption of starlight in the EGP atmosphere. Of these effects, molecular absorption dominates in deter…
High-Resolution X-Ray Spectroscopy and Modeling of the Absorbing and Emitting Outflow in NGC 3783
Brandt, W. N.; Kaspi, Shai; Garmire, Gordon P. +6 more
The high-resolution X-ray spectrum of NGC 3783 shows several dozen absorption lines and a few emission lines from the H-like and He-like ions of O, Ne, Mg, Si, and S, as well as from Fe XVII-Fe XXIII L-shell transitions. We have reanalyzed the Chandra HETGS spectrum using better flux and wavelength calibrations, along with more robust methods. Com…