Search Publications
A Wide Field Planetary Camera 2 Study of the Resolved Stellar Population of the Pegasus Dwarf Irregular Galaxy (DDO 216)
Saha, A.; Mateo, M.; Gallagher, J. S. +5 more
The stellar population of the Pegasus dwarf irregular galaxy is investigated in images taken in the F439W (B), F555W (V), and F814W (I) bands with the Wide Field Planetary Camera 2 (WFPC2) on the Hubble Space Telescope. With WFPC2 the Pegasus dwarf is highly resolved into individual stars to limiting magnitudes of about 25.5 in B and V and 25 in I…
Deep Hubble Space Telescope Observations of Star Clusters in NGC 1275
Ballester, Gilda E.; Crisp, David; Grillmair, Carl J. +15 more
We present an analysis of compact star clusters in deep Hubble Space Telescope Wide Field Planetary Camera 2 images of NGC 1275. B- and R-band photometry of roughly 3000 clusters shows a bimodality in the B - R colors, suggesting that distinct old and young cluster populations are present. The small spread in the colors of the blue clusters is con…
Spatially Resolved Hubble Space Telescope Spectra of the Chromosphere of alpha Orionis
Dupree, A. K.; Gilliland, R. L.; Uitenbroek, H.
Spatially resolved UV spectra of the supergiant alpha Orionis (Betelgeuse) obtained in 1995 March with the Goddard High Resolution Spectrograph (GHRS) on board the Hubble Space Telescope (HST) show that the chromospheric emission in the Mg II h and k (around 280 nm) lines reaches a diameter of at least ~270 milliarcseconds, about twice the size of…
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…