Search Publications
An Intermediate-Mass Black Hole in the Globular Cluster G1: Improved Significance from New Keck and Hubble Space Telescope Observations
Ho, Luis C.; Gebhardt, Karl; Rich, R. M.
We present dynamical models for the massive globular cluster G1. The goal is to measure or place a significant upper limit on the mass of any central black hole. Whether or not globular clusters contain central massive black holes has important consequences for a variety of studies. We use new kinematic data obtained with Keck and new photometry f…
What controls the CIV line profile in active galactic nuclei?
Laor, Ari; Baskin, Alexei
The high-ionization lines in active galactic nuclei (AGN), such as CIV, tend to be blueshifted with respect to the lower-ionization lines, such as Hβ, and often show a strong blue excess asymmetry not seen in the low-ionization lines. There is accumulating evidence that the Hβ profile is dominated by gravity, and thus provides a useful estimate of…
The Assembly History of Field Spheroidals: Evolution of Mass-to-Light Ratios and Signatures of Recent Star Formation
Treu, Tommaso; van Dokkum, Pieter G.; Coil, Alison +6 more
We present a comprehensive catalog of high signal-to-noise ratio spectra obtained with DEIMOS on the Keck II telescope for a sample of F850LP<22.43 (AB) field spheroidal (E+S0 galaxies; 165) and bulge-dominated disk (61) galaxies in the redshift range 0.2<z<1.2, selected on the basis of visual morphology from the northern field of the Gre…
Lower mass loss rates in O-type stars: Spectral signatures of dense clumps in the wind of two Galactic O4 stars
Bouret, J. -C.; Hillier, D. J.; Lanz, T.
We have analyzed the far-ultraviolet spectrum of two Galactic O4 stars, the O4If+ supergiant HD 190429A and the O4V((f)) dwarf HD 96715, using archival FUSE and IUE data. We have conducted a quantitative analysis using the two NLTE model atmosphere and wind codes, tlusty and cmfgen, which incorporate a detailed treatment of NLTE metal line blanket…
Relativistic Accretion Disk Models of High-State Black Hole X-Ray Binary Spectra
Hubeny, Ivan; Davis, Shane W.; Turner, Neal J. +1 more
We present calculations of non-LTE, relativistic accretion disk models applicable to the high/soft state of black hole X-ray binaries. We include the effects of thermal Comptonization and bound-free and free-free opacities of all abundant ion species. Taking into account the relativistic propagation of photons from the local disk surface to an obs…
HST STIS Spectroscopy of the Triple Nucleus of M31: Two Nested Disks in Keplerian Rotation around a Supermassive Black Hole
Richstone, Douglas; Kormendy, John; Lauer, Tod R. +12 more
We present Hubble Space Telescope (HST) spectroscopy of the nucleus of M31 obtained with the Space Telescope Imaging Spectrograph (STIS). Spectra that include the Ca II infrared triplet (λ~=8500 Å) see only the red giant stars in the double brightness peaks P1 and P2. In contrast, spectra taken at λ~=3600-5100 Å are sensitive to the tiny blue nucl…
Stellar Lyα Emission Lines in the Hubble Space Telescope Archive: Intrinsic Line Fluxes and Absorption from the Heliosphere and Astrospheres
Zank, Gary P.; Redfield, Seth; Wood, Brian E. +2 more
We search the Hubble Space Telescope (HST) archive for previously unanalyzed observations of stellar H I Lyα emission lines, our primary purpose being to look for new detections of Lyα absorption from the outer heliosphere and to also search for analogous absorption from the astrospheres surrounding the observed stars. The astrospheric absorption …
Stellar Populations in 10 Clump-Cluster Galaxies of the Hubble Ultra Deep Field
Elmegreen, Bruce G.; Elmegreen, Debra Meloy
Color-color diagrams for the clump and interclump emission in 10 clump-cluster galaxies of the Hubble Ultra Deep Field (UDF) are made from B,V, i, and z images and compared with models to determine redshifts, star formation histories, and galaxy masses. These galaxies are members of a class dominated by 5-10 giant clumps, with no exponential disk …
Radar Soundings of the Ionosphere of Mars
Gurnett, D. A.; Persoon, A. M.; Averkamp, T. F. +8 more
We report the first radar soundings of the ionosphere of Mars with the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument on board the orbiting Mars Express spacecraft. Several types of ionospheric echoes are observed, ranging from vertical echoes caused by specular reflection from the horizontally stratified ionosphere…
Differentiation of the asteroid Ceres as revealed by its shape
Russell, C. T.; Stern, S. A.; Young, E. F. +4 more
The accretion of bodies in the asteroid belt was halted nearly 4.6billion years ago by the gravitational influence of the newly formed giant planet Jupiter. The asteroid belt therefore preserves a record of both this earliest epoch of Solar System formation and variation of conditions within the solar nebula. Spectral features in reflected sunligh…