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Mass Segregation in Young Large Magellanic Cloud Clusters. I. NGC 2157
Mateo, Mario; Pryor, Carlton; Fischer, Philippe +2 more
We have carried out Wide Field Planetary Camera 2 V- and I-band imaging of the young LMC cluster NGC 2157. Construction of a color-magnitude diagram and isochrone fitting yield an age of tau = 10^8 yr, a reddening E(B - V) = 0.1, and a distance modulus of 18.4 mag. Our data cover the mass range 0.75 M_⊙ <= m <= 5.1 M_⊙. We find that the clus…
Star Formation in and Evolution of the Blue Compact Dwarf Galaxy UGC 6456 Determined from Hubble Space Telescope Images
Tolstoy, Eline; Lynds, Roger; O'Neil, Earl J., Jr. +1 more
Photometry on the UVI system has been performed on the resolved stellar content of the blue compact dwarf galaxy UGC 6456 using Wide Field Planetary Camera 2 (WFPC2) images obtained with the Hubble Space Telescope. The resulting color-magnitude diagram (CMD) goes to about V = 27.5 and reveals not only a young population of blue main-sequence stars…
A Study of Nine High-Redshift Clusters of Galaxies. III. Hubble Space Telescope Morphology of Clusters 0023+0423 and 1604+4304
Schneider, Donald P.; Postman, Marc; Hoessel, John G. +4 more
We present a detailed morphological analysis of the galaxy populations in the first two clusters to be completed in an extensive observational study of nine high-redshift clusters of galaxies. These two clusters, Cl 0023+0423 and Cl 1604+4304, are at redshifts of z = 0.84 and z = 0.90, respectively. The morphological studies are based on high angu…
A Search for Star Clusters from the HIPPARCOS Data
van Leeuwen, Floor; Kozhurina-Platais, Vera; Platais, Imants
We present results of a search for nearby star clusters and associations using Hipparcos Catalogue data, restricting the sample to stars with parallaxes above 2 mas (d <~ 500 pc). Two new OB associations have been identified in the Carina-Vela and Cepheus-Cygnus-Lyra-Vulpecula regions. A very probable new open cluster has been discovered in Car…
Proper Motions in the Ejecta of η Carinae with a 50 Year Baseline
Smith, Nathan; Gehrz, Robert D.
Observations of η Carinae from three separate epochs spanning a total of 50 years are used to measure the proper motions of several easily identifiable features in the Homunculus Nebula. Our principal conclusion is that the equatorial features were ejected significantly after the ``Great Eruption,'' very likely in the outburst that occurred around…
Galactic Interior Motions Derived from HIPPARCOS Proper Motions. I. Young Disk Population
Zhu, Zi; Miyamoto, Masanori
Analyzing Hipparcos proper motions of 1352 O-B5 stars other than the Gould belt stars, which are representative of the young disk population, we have found a clear stellar warping motion that is a systematic rotation +3.8 +/- 1.1 km s^-1 kpc^-1 of stars about the axis pointing to the Galactic center in the sense of increasing the inclination of th…
Hubble Space Telescope Detection of Optical Companions of WR 86, WR 146, and WR 147: Wind Collision Model Confirmed
Zurek, David R.; Moffat, Anthony F. J.; Wallace, Debra J. +2 more
Hubble Space Telescope (HST) Wide Field Planetary Camera 2 images of the rado-binary Wolf-Rayet stars WR 146 and WR 147, as well as the 0.2" visual binary WR 86, resolve each of them into two very close optical components. The colors of these optical pairs are similar, indicating that they are likely to be physically bound WR + OB systems at the s…
The Hot Stars of Old Open Clusters: M67, NGC 188, and NGC 6791
O'Connell, Robert W.; Bohlin, Ralph C.; Landsman, Wayne +4 more
We analyze ultraviolet (~1500 Å) images of the old open clusters M67, NGC 188, and NGC 6791 obtained with the Ultraviolet Imaging Telescope (UIT) during the second flight of the Astro observatory in 1995 March. Twenty stars are detected on the UIT image of M67, including 11 blue stragglers, seven white dwarf candidates, and the yellow giant-white …
The Infrared Morphology of eta Carinae
Smith, Nathan; Gehrz, Robert D.; Krautter, Joachim
We present results of a recent 2-12 µm ground-based infrared (IR) imaging study of Eta Carinae. We discuss the comparative spatial morphology of the bipolar lobes, the ``skirt'' defined by the equatorial ejecta, and the bright features in the core. We derive separate color temperature values of 200, 240, and 420 K for the bipolar lobes, skir…
On the Use of [Na/Fe] and [alpha/Fe] Ratios and Hipparcos-based (U, V, W) Velocities as Age Indicators among Low-Metallicity Halo Field Giants
Sneden, Christopher; Hanson, Robert B.; Kraft, Robert P. +1 more
We have examined the [Na/Fe] and [Mg/Fe] ratios in a sample of 68 field halo giants with -3 <~ [Fe/H] <~ -1. We recalculated the Galactic (U, V, W) velocity components for these stars, using Hipparcos proper motions and a new Hipparcos-based distance scale. We used these data to see how the abundance ratios may relate to kinematical substruc…