Search Publications
Detailed Structural Decomposition of Galaxy Images
Ho, Luis C.; Rix, Hans-Walter; Peng, Chien Y. +1 more
We present a two-dimensional fitting algorithm (GALFIT) designed to extract structural components from galaxy images, with emphasis on closely modeling light profiles of spatially well-resolved, nearby galaxies observed with the Hubble Space Telescope. Our algorithm improves on previous techniques in two areas: by being able to simultaneously fit …
The Observed Offset Distribution of Gamma-Ray Bursts from Their Host Galaxies: A Robust Clue to the Nature of the Progenitors
Bloom, J. S.; Djorgovski, S. G.; Kulkarni, S. R.
We present a comprehensive study to measure the locations of gamma-ray bursts (GRBs) relative to their host galaxies. In total, we find the offsets of 20 long-duration GRBs from their apparent host galaxy centers by utilizing ground-based images from Palomar and Keck and space-based images from the Hubble Space Telescope (HST). We discuss in detai…
Astrometry and Photometry for Cool Dwarfs and Brown Dwarfs
Kirkpatrick, J. Davy; Burgasser, Adam J.; Gizis, John E. +15 more
Trigonometric parallax determinations are presented for 28 late-type dwarfs and brown dwarfs, including eight M dwarfs with spectral types between M7 and M9.5, 17 L dwarfs with spectral types between L0 and L8, and three T dwarfs. Broadband photometry at CCD wavelengths (VRIz*) and/or near-IR wavelengths (JHK) is presented for these objects and fo…
A Hubble Space Telescope Census of Nuclear Star Clusters in Late-Type Spiral Galaxies. I. Observations and Image Analysis
Böker, Torsten; Ho, Luis C.; Shields, Joseph C. +4 more
We present new Hubble Space Telescope I-band images of a sample of 77 nearby late-type spiral galaxies with low inclination. The main purpose of this catalog is to study the frequency and properties of nuclear star clusters. In 59 galaxies of our sample, we have identified a distinct, compact (but resolved), and dominant source at or very close to…
Exploring the Full Stellar Population of the Upper Scorpius OB Association
Brown, Anthony G. A.; Zinnecker, Hans; Guenther, Eike +2 more
We investigate the stellar population and star formation history of the Upper Scorpius OB association, the most nearby region of recent massive star formation, over the full stellar mass range from 0.1 to 20 Msolar. The first part of this paper describes an extension of our large spectroscopic survey (Preibisch et al., published in 2001…
Post-T Tauri Stars in the Nearest OB Association
Meyer, Michael R.; Mamajek, Eric E.; Liebert, James
We present results of a spectroscopic survey of X-ray- and proper-motion-selected samples of late-type stars in the Lower Centaurus-Crux (LCC) and Upper Centaurus-Lupus (UCL) subgroups of the nearest OB association: Scorpius-Centaurus. The primary goals of the survey are to determine the star formation history of the OB subgroups and to assess the…
A New Spectral Classification System for the Earliest O Stars: Definition of Type O2
Walborn, Nolan R.; Parker, Joel Wm.; Drissen, Laurent +7 more
High-quality, blue-violet spectroscopic data are collected for 24 stars that have been classified as type O3 and that display the hallmark N IV and N V lines. A new member of the class is presented; it is the second known in the Cyg OB2 association, and only the second in the northern hemisphere. New digital data are also presented for several of …
Hubble Space Telescope Evidence for an Intermediate-Mass Black Hole in the Globular Cluster M15. II. Kinematic Analysis and Dynamical Modeling
Gerssen, Joris; van der Marel, Roeland P.; Gebhardt, Karl +3 more
We have used the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) to obtain high spatial resolution spectroscopy of the central region of the dense globular cluster M15. The observational strategy and data reduction were described in Paper I of this series. Here we analyze the extracted spectra with a cross-correlati…
The Palomar/MSU Nearby Star Spectroscopic Survey. IV. The Luminosity Function in the Solar Neighborhood and M Dwarf Kinematics
Hawley, Suzanne L.; Gizis, John E.; Reid, I. Neill
We have used new astrometric and spectroscopic observations to refine the volume-complete sample of M dwarfs defined in previous papers in this series. With the addition of Hipparcos astrometry, our revised VC2 sample includes 558 main-sequence stars in 448 systems. Analysis of that data set shows no evidence of any systematic kinematic…
Large-Amplitude X-Ray Outbursts from Galactic Nuclei: A Systematic Survey using ROSAT Archival Data
Brandt, W. N.; Eracleous, Michael; Boller, Th. +1 more
In recent years, luminous X-ray outbursts with variability amplitudes as high as ~400 have been serendipitously detected from a small number of active and inactive galaxies. These outbursts may result from the tidal disruptions of stars by supermassive black holes, as well as accretion disk instabilities. In order to place the first reliable const…