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A HIPPARCOS Census of the Nearby OB Associations
Brown, A. G. A.; de Bruijne, J. H. J.; de Zeeuw, P. T. +2 more
A comprehensive census of the stellar content of the OB associations within 1 kpc from the Sun is presented, based on Hipparcos positions, proper motions, and parallaxes. It is a key part of a long-term project to study the formation, structure, and evolution of nearby young stellar groups and related star-forming regions. OB associations are unbo…
Radii and Effective Temperatures for G, K, and M Giants and Supergiants
Kulkarni, S. R.; Palmer, D.; van Belle, G. T. +13 more
Interferometrically determined angular diameters obtained at the Palomar Testbed Interferometer (PTI) for 69 giant and supergiant stars are presented. Spectral types of the 59 giant stars generally lie between G6 and M6, although a B7 giant is included; the nine bright giants and supergiants have spectral types between F5 and M5. Comparison of the…
The Age, Extinction, and Distance of the Old, Metal-rich Open Cluster NGC 6791
Chaboyer, Brian; Liebert, James; Green, Elizabeth M.
An extensive grid of metal-rich isochrones utilizing the latest available input physics has been calculated for comparison with the old, metal-rich open cluster NGC 6791. The isochrones have been simultaneously fitted to BV and VI color-magnitude diagrams, with the same composition, reddening, and distance modulus required for both colors. Our bes…
Space Velocities of Southern Globular Clusters. II. New Results for 10 Clusters
Girard, Terrence M.; van Altena, William F.; López, Carlos E. +1 more
Absolute proper motions have been measured for 10 clusters, in addition to the sample of five clusters presented in an earlier paper. These newly measured clusters are NGC 1904 (M79), NGC 2298, NGC 4590 (M68), NGC 5139 (omega Cen), NGC 5897, NGC 6093 (M80), NGC 6121 (M4), NGC 6144, NGC 6809 (M55), and NGC 7099 (M30). The correction to absolute pro…
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,'' …
Stellar Encounters with the Oort Cloud Based on HIPPARCOS Data
Latham, David W.; García-Sánchez, Joan; Preston, Robert A. +4 more
We have combined Hipparcos proper-motion and parallax data for nearby stars with ground-based radial velocity measurements to find stars that may have passed (or will pass) close enough to the Sun to perturb the Oort cloud. Close stellar encounters could deflect large numbers of comets into the inner solar system, which would increase the impact h…
Zeroing the Stellar Isochrone Scale: The Red Giant Clump Luminosity at Intermediate Metallicity
Twarog, Bruce A.; Anthony-Twarog, Barbara J.; Bricker, Andrew R.
The color-magnitude diagrams of the open clusters NGC 2420 and NGC 2506 have been investigated as intermediate links between the solar neighborhood and the Magellanic Clouds. Two sets of theoretical isochrones that include convective overshoot are zeroed to the Sun at solar abundance and to the unevolved main-sequence dwarfs of the Hipparcos Catal…
Speckle Observations of Binary Stars with the WIYN Telescope. I. Measures During 1997
Girard, Terrence M.; van Altena, William F.; Horch, Elliott +3 more
Two hundred seventy-seven position angle and separation measures of 154 double stars are presented. Three of the systems were previously unknown to be double, and 16 other systems were discovered earlier this decade by the Hipparcos satellite. Measures are derived from speckle observations taken with the Wisconsin-Indiana-Yale-NOAO (WIYN) 3.5 m te…
Determining the Galactic Mass Distribution Using Tidal Streams from Globular Clusters
Murali, Chigurupati; Dubinski, John
We discuss how to use tidal streams from globular clusters to measure the mass distribution of the Milky Way. Recent proper-motion determinations for globular clusters from plate measurements and Hipparcos astrometry provide several good candidates for Galactic mass determinations in the intermediate halo far above the Galactic disk, including Pal…
A Large H I Shell surrounding the Wolf-Rayet Star HD 191765
St-Louis, Nicole; Gervais, Simon
We have surveyed a 2.6dx2.6d field centered on the Wolf-Rayet (W-R) star HD 191765 (=WR 134) in the H I 21 cm line and in the 1420 and 408 MHz radio continuum, using the Synthesis Telescope of the Dominion Radio Astrophysical Observatory, to search for direct evidence of the interaction between the W-R star wind and the interstellar medium. An arc…