Search Publications
B2045+265: A New Four-Image Gravitational Lens from CLASS
Pearson, T. J.; Bremer, M.; Blandford, R. D. +14 more
We have discovered a new gravitational lens in the Cosmic Lens All-Sky Survey (CLASS). The lens B2045+265 is a four-image system with a maximum separation of 1.9". A fifth radio component is detected, but its radio spectrum and its positional coincidence with infrared emission from the lensing galaxy strongly suggest that it is the radio core of t…
CO Band Head Spectroscopy of IC 342: Mass and Age of the Nuclear Star Cluster
Böker, Torsten; van der Marel, Roeland P.; Vacca, William D.
We have used the NASA Infrared Telescope Facility (IRTF) to observe the nuclear stellar cluster in the nearby, face-on, giant Scd spiral IC 342. From high-resolution (lambda/Deltalambda=21,500) spectra of the ^12CO (2-0) band head at 2.3 mum, we derive a line-of-sight stellar velocity dispersion sigma=(33+/-3) km s^-1. To interpret this observatio…
Stellar Populations at the Center of IC 1613
Cole, Andrew A.; Ballester, Gilda E.; Krist, John E. +18 more
We have observed the center of the Local Group dwarf irregular galaxy IC 1613 with the WFPC2 aboard the Hubble Space Telescope in the F439W, F555W, and F814W filters. We analyze the resulting color-magnitude diagrams (CMDs) using the main-sequence and giant-branch luminosity functions and comparisons with theoretical stellar models to derive a pre…
Speckle Interferometry of New and Problem HIPPARCOS Binaries
Mason, Brian D.; ten Brummelaar, Theo; Barry, Donald J. +7 more
The ESA Hipparcos satellite made measurements of over 12,000 double stars and discovered 3406 new systems. In addition to these, 4706 entries in the Hipparcos Catalogue correspond to double star solutions that did not provide the classical parameters of separation and position angle (rho,theta) but were the so-called problem stars, flagged ``G,'' …
HUBBLE SPACE TELESCOPE Observations of Galactic Globular Cluster Cores. II. NGC 6273 and the Problem of Horizontal-Branch Gaps
Djorgovski, S. G.; Zoccali, M.; Rich, R. M. +4 more
We present observations of the center of the Galactic globular cluster NGC 6273, obtained with the Hubble Space Telescope Wide Field Planetary Camera 2 as part of the snapshot program GO-7470. A BV color-magnitude diagram (CMD) for ~28,000 stars is presented and discussed. The most prominent feature of the CMD, identified for the first time in thi…
Very High Resolution Ultraviolet Spectroscopy of a Chemically Peculiar Star: Results of the chi LUPI Pathfinder Project
Wahlgren, Glenn M.; Proffitt, Charles R.; Brage, Tomas +2 more
We summarize here the results of a major eight-year investigation of the extraordinarily detailed UV spectrum of the sharp-lined, nonmagnetic, main-sequence, chemically peculiar star chi Lupi (B9.5p HgMn + A2 Vm). The UV observations are composed of 345 Å of the spectrum acquired with the Goddard High Resolution Spectrograph (GHRS) on board the Hu…
WFPC2 Observations of Compact Star Cluster Nuclei in Low-Luminosity Spiral Galaxies
Ballester, Gilda E.; Krist, John E.; Crisp, David +15 more
We have used the Wide Field Planetary Camera 2 (WFPC2) aboard the Hubble Space Telescope to obtain F450W and F814W (B- and I-band) observations of the compact star cluster nuclei of the nearby, late-type, low-luminosity spiral galaxies NGC 4395, NGC 4242, and ESO 359-029. In addition, we analyze archival WFPC2 observations of the compact star clus…
Hubble Space Telescope Measurements of the Expansion of NGC 6543: Parallax Distance and Nebular Evolution
Casertano, Stefano; Panagia, Nino; Balick, Bruce +5 more
The optical expansion parallax of NGC 6543 has been detected and measured using two epochs of Hubble Space Telescope images separated by a time baseline of only 3 years. We have utilized three separate methods of deriving the angular expansion of bright fiducials, with excellent agreement in the results. We combine our angular expansion estimates …
An Unusual Brightening Of Eta Carinae
Gull, Theodore R.; Humphreys, Roberta M.; Davidson, Kris +7 more
HST/Space Telescope Imaging Spectrograph data show that the apparent near-UV, visual-wavelength, and near-IR brightness of η Car increased by a factor of two during 1998. Meanwhile its Homunculus ejecta nebula brightened by about 30%, the largest fluctuation of this type in the past 40 years. These developments were quite unexpected and are not ea…
The Deuterium Abundance at z=0.701Z = 0.701 toward QSO 1718+4807
Savage, Blair D.; Lu, Limin; Burles, Scott +3 more
We present constraints on the deuterium-to-hydrogen ratio (D/H) in the metal-poor gas cloud at redshift z=0.701 toward QSO 1718+4807. We use new Keck spectra in addition to Hubble Space Telescope (HST) and International Ultraviolet Explorer spectra. We use an improved redshift and a lower H I column density to model the absorption. The HST spectru…