Search Publications
The Close Magnetic/Nonmagnetic Double-degenerate Binary LB 11146
Liebert, James; Schmidt, Gary D.; Smith, Paul S.
Spacecraft imaging of the remarkable strongly magnetic/nonmagnetic white dwarf binary system LB 11146 establishes an upper limit to the component separation of 0.025", corresponding to a 90% likelihood that the orbital separation is a < 500 R_⊙. The large and nearly identical inferred masses for the two components make it very likely that some …
The Pleiades and alpha Persei Clusters
Eggen, Olin J.
The upper-main-sequence members of the Pleiades and alpha Persei clusters, considered as members of the Local Association, yield mean parallaxes that are only 4% larger than the mean values from Hipparcos observations. The (log T_eff, M_V) diagram reveals that in the temperature range from 6000 to 8000 K, the Hyades and alpha Persei main-sequence …
Galaxies with Spiral Structure up to Z ~ 0.87: Limits on M/L and the Stellar Velocity Dispersion
Quillen, A. C.; Sarajedini, V. L.
We consider seven distant galaxies with clearly evident spiral structure from Hubble Space Telescope images. We place upper limits on their mass-to-light ratios (M/L) by computing M/L_B for a maximal disk. We find that these galaxies have maximal-disk mass-to-light ratios M/L_B = 1.5-3.5 (M/L_B)_⊙ at the low end, but within the range seen in nearb…
Serendipitous Discovery of a Broad Absorption Line QSO at Z = 2.169
Roth, Katherine C.; Stockton, Alan; Canalizo, Gabriela
We report the serendipitous discovery of a broad absorption line (BAL) QSO at z = 2.169, located 41" southwest of 3C 48. We present Keck Low Resolution Imaging Spectrometer spectroscopy covering rest-frame wavelengths 1500-2300 Å. The C iv BAL has three components, and it extends to outflow velocities of at least 12,000 km s^-1. The BAL QSO has an…
Hubble Space Telescope Observations of Chromospheric Emission from the Population II Red Giant HD 216143
Smith, Graeme H.; Dupree, A. K.
Spectra of the Hα and Ca ii K line of Population II red giants exhibit evidence for chromospheric mass outflows only among stars brighter than M_V = -1.7. In order to determine whether this phenomenon is indicative of a true physical onset in mass outflow, spectra of the 2800 Å Mg ii lines of the metal-poor halo red giant HD 216143 have been obtai…
Wide Field Planetary Camera 2 Observations of Proxima Centauri: No Evidence of the Possible Substellar Companion
Golimowski, David A.; Schroeder, Daniel J.
Two-epoch observations of Proxima Centauri using the Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC2) are reported. Exposures of 10 and 40 s were recorded through the F1042M filter (lambda_c ~ 1 µm), permitting examination of the circumstellar region beyond 0.09" from Proxima Cen. No evidence of a substellar companion withi…
Optimal Proper-Motion Measurements with the Wide Field and Planetary Camera
Lewis, Geraint F.; Ibata, Rodrigo A.
An optimal maximum-likelihood technique for computing point-source image centroids from many, slightly offset, CCD frames is presented. The method is especially useful for measuring stellar proper motions from data taken with the Wide Field and Planetary Camera on board the Hubble Space Telescope, and also provides a means to identify very compact…
CCD Positions for the Outer Planets in 1996-1997 Determined in the Extragalactic Reference Frame
Stone, Ronald C.
This paper presents 316 new equatorial positions for the planets Uranus, Neptune, and Pluto obtained in 1996-1997 with the Flagstaff Astrometric Scanning Transit Telescope (FASTT). All the positions were determined in the extragalactic reference frame using CCD observations and are accurate to ~+/-0.2" in each coordinate. When these positions are …
Hubble Space Telescope Resolved Image and Spectra of the Z ~= 2 QSO 1345+584
Hutchings, J. B.
QSO 1345+584 has been spatially resolved by direct images and in spectral images, and has asymmetrically extended flux to the west, where its inner radio structure is seen. The brightest knots in the resolved flux correspond closely with knots in the curved radio jet, and the brightest knot has a velocity of approach of some 3000 km s^-1 with resp…
The Red Horizontal-Branch Star HD 17072
Lee, Jae-Woo; Carney, Bruce W.; Habgood, Michael J.
We summarize the results of a spectroscopic analysis of HD 17072, finding it to be a metal-poor ([Fe/H] = -1.17) red horizontal-branch star with T_eff = 5375 K and log g = 2.4. We also derive a radial velocity of 62.8 km s^-1. It has the best determined Hipparcos trigonometric parallax among the metal-poor field horizontal-branch stars and support…