Search Publications
K-Band Calibration of the Red Clump Luminosity
Alves, David R.
The average near-infrared (K-band) luminosity of 238 Hipparcos red clump giants is derived and then used to measure the distance to the Galactic center. These Hipparcos red clump giants have been previously employed as I-band standard candles. The advantage of the K-band is a decreased sensitivity to reddening and perhaps a reduced systematic depe…
The MACHO Project: Microlensing Optical Depth toward the Galactic Bulge from Difference Image Analysis
Alcock, C.; Allsman, R. A.; Alves, D. R. +22 more
We present the microlensing optical depth toward the Galactic bulge based on the detection of 99 events found in our Difference Image Analysis (DIA) survey. This analysis encompasses 3 yr of data, covering ~17 million stars in ~4 deg2, to a source-star baseline magnitude limit of V=23. The DIA technique improves the quality of photometr…
X-Ray and Optical Variability in NGC 4051 and the Nature of Narrow-Line Seyfert 1 Galaxies
Vestergaard, M.; Papadakis, I.; Peterson, B. M. +14 more
We report on the results of a three-year program of coordinated X-ray and optical monitoring of the narrow-line Seyfert 1 galaxy NGC 4051. The rapid continuum variations observed in the X-ray spectra are not detected in the optical, although the time-averaged X-ray and optical continuum fluxes are well correlated. Variations in the flux of the bro…
Space Telescope Imaging Spectrograph Coronagraphic Observations of β Pictoris
Hubeny, Ivan; Woodgate, Bruce; Heap, Sara R. +4 more
We present new coronagraphic images of β Pictoris obtained with the Space Telescope Imaging Spectrograph (STIS) in 1997 September. The high-resolution images (0.1") clearly detect the circumstellar disk as close to the star as 0.75", corresponding to a projected radius of 15 AU. The images define the warp in the disk with greater precision and at …
Hubble Space Telescope Weak-Lensing Study of the z=0.83 Cluster MS 1054-03
Hoekstra, H.; Franx, M.; Kuijken, K.
We have measured the weak gravitational lensing of faint, distant background galaxies by MS 1054-03, a rich and X-ray luminous cluster of galaxies at a redshift of z=0.83, using a two-color mosaic of deep WFPC2 images. The small corrections for the size of the point-spread function and the high number density of background galaxies obtained in the…
The Structure and Emission of the Accretion Shock in T Tauri Stars. II. The Ultraviolet-Continuum Emission
Hartmann, Lee; Calvet, Nuria; Muzerolle, James +1 more
We compare accretion-shock models with optical and ultraviolet spectra of pre-main-sequence stars to (1) make the first determinations of accretion rates in intermediate-mass T Tauri stars from continuum emission and (2) derive improved estimates of accretion rates and extinctions for continuum T Tauri stars. Our method extends the shock models de…
Hubble Space Telescope STIS Spectroscopy of the Optical Outflow from DG Tauri: Structure and Kinematics on Subarcsecond Scales
Bacciotti, Francesca; Eislöffel, Jochen; Mundt, Reinhard +3 more
We have carried out a spatio-kinematic study of the outflow from the classical T Tauri star DG Tau using the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope. A series of seven spatially offset long-slit spectra spaced by 0.07" were obtained along the axis of the outflow to build up a three-dimensional intensity-velo…
The Fundamental Plane of Gravitational Lens Galaxies and The Evolution of Early-Type Galaxies in Low-Density Environments
Peng, C. Y.; Keeton, C. R.; Kochanek, C. S. +6 more
Most gravitational lenses are early-type galaxies in relatively low density environments-a ``field'' rather than a ``cluster'' population. Their average properties are the mass-averaged properties of all early-type galaxies. We show that field early-type galaxies with 0<z<1, as represented by the lens galaxies, lie on the same fundamental pl…
Jet-induced Emission-Line Nebulosity and Star Formation in the High-Redshift Radio Galaxy 4C 41.17
Dey, Arjun; Dopita, Michael A.; Sutherland, Ralph S. +3 more
The high-redshift radio galaxy 4C 41.17 has been shown in earlier work to consist of a powerful radio source in which there is strong evidence for jet-induced star formation along the radio axis. We argue that nuclear photoionization is not responsible for the excitation of the emission line clouds, and we construct a jet-cloud interaction model t…
Identification of a Nearby Stellar Association in theHipparcos Catalog: Implications for Recent, Local Star Formation
Zuckerman, B.; Webb, R. A.
The TW Hydrae Association (~55 pc from Earth) is the nearest known region of recent star formation. Based primarily on the Hipparcos catalog, we have identified a group of nine or 10 comoving star systems at a common distance (~45 pc) from Earth that appear to comprise another, somewhat older association (``the Tucanae Association''). Together wit…