Steinn Sigurdsson

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The capture and subsequent inspiral of stellar mass black holes on eccentric orbits by central massive black holes, is one of the more interesting likely sources of gravitational radiation detectable by LISA. We estimate the rate of observable events and the associated uncertainties. A moderately favourable mass function could provide many detectable bursts(More)
We present the results of a study that uses numerical simulations to interpret observations of tidally disturbed satellites around the Milky Way. When analysing the simulations from the viewpoint of an observer, we find a break in the slope of the star count and velocity dispersion profiles in our models at the location where unbound stars dominate. We(More)
We investigate the possible progenitors of the planetary nebulae (PNs) which populate the top 0.5 mag of the [O III] λ5007 planetary nebula luminosity function (PNLF). We show that the absolute luminosity of the PNLF cutoff demands that the central stars of these most luminous planetaries be & 0.6M⊙, and that such high-mass PN cores must exist in every(More)
We have used the WFPC2 camera of the Hubble Space Telescope to obtain deep F814W images of a blank field in the Virgo Cluster located 41 northwest of M87. We perform star counts in that field, and in another Virgo field observed by Ferguson, Tanvir, & von Hippel (1998), and show that, when compared to the Hubble Deep Field North and South, the Virgo Cluster(More)
The pulsar B1620-26 has two companions, one of stellar mass and one of planetary mass. We detected the stellar companion with the use of Hubble Space Telescope observations. The color and magnitude of the stellar companion indicate that it is an undermassive white dwarf (0.34 +/- 0.04 solar mass) of age 480 x 10(6) +/- 140 x 10(6) years. This places a(More)
Close-in giant planets (e.g., "hot Jupiters") are thought to form far from their host stars and migrate inward, through the terrestrial planet zone, via torques with a massive gaseous disk. Here we simulate terrestrial planet growth during and after giant planet migration. Several-Earth-mass planets also form interior to the migrating jovian planet,(More)
We describe and characterize a 25 GHz laser frequency comb based on a cavity-filtered erbium fiber mode-locked laser. The comb provides a uniform array of optical frequencies spanning 1450 nm to 1700 nm, and is stabilized by use of a global positioning system referenced atomic clock. This comb was deployed at the 9.2 m Hobby-Eberly telescope at the McDonald(More)
Stars and compact objects that plunge toward a black hole are either 1) captured, emitting gravitational waves as the orbit decays, 2) tidally disrupted, leaving a disc of baryonic material, 3) scattered to a large radius, where they may thereafter avoid encounters with the black hole or 4) swallowed whole, contributing to black hole growth. These processes(More)
We use numerical simulations to study the evolution of triaxial elliptical galaxies with central black holes. In contrast to earlier studies which used galaxy models with central density “cores,” our galaxies have steep central cusps, as observed in real ellipticals. As a black hole grows in these cuspy triaxial galaxies, the inner regions become rounder(More)