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Doppler Shifts in the Quiet-Sun Transition Region and Corona Observed with SUMER on SOHO
Wilhelm, K.; Brekke, P.; Hassler, D. M.
New observations of systematic red shifts of transition region and coronal lines obtained with SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on SOHO (the Solar and Heliospheric Observatory) are presented. With the extensive wavelength coverage of SUMER it is possible to extend the measurements of the red shifts to much higher tempera…
A Comparison of Direct and Indirect Mass Estimates for Distant Clusters of Galaxies
Smail, Ian; Ellis, Richard S.; Dressler, Alan +4 more
We present weak lensing results for 12 distant clusters determined from images obtained with the refurbished Hubble Space Telescope. We detect the signature of gravitational lensing in 11 of the 12 clusters; the clusters span nearly 1 order of magnitude in lensing strength. The sample thus provides an excellent database for correlating direct mass…
Fundamental parameters of Wolf-Rayet stars. VI. Large Magellanic Cloud WNL stars.
Crowther, P. A.; Smith, L. J.
We present a detailed, quantitative study of late WN (WNL) stars in the LMC, based on new optical spectroscopy (AAT, MSO) and the Hillier (1990A&A...231..111H) atmospheric model. In a previous paper (Crowther et al. 1995A&A...293..172C), we showed that 4 out of the 10 known LMC Ofpe/WN9 stars should be re-classified WN9-10. We now present …
SBS 0335-052, A Probable Nearby Young Dwarf Galaxy: Evidence Pro and Con
Chaffee, Frederic H.; Izotov, Yuri I.; Foltz, Craig B. +3 more
The results of Multiple Mirror Telescope spectrophotometry of the extremely low metallicity blue compact galaxy (BCG) SBS 0335-052 (SBS--the Second Byurakan Survey) are presented. The oxygen abundance in the central, brightest part of the galaxy is found to be 12 + log (O/H) = 7.33 +/- 0.01, only slightly greater than the oxygen abundance in the m…
First results from HIPPARCOS trigonometrical parallaxes of Mira-type variables
van Leeuwen, F.; Whitelock, P. A.; Feast, M. W. +1 more
HIPPARCOS trigonometrical parallaxes are given for 16 pre-selected Mira variables. Linear diameters are derived for eight oxygen-rich Miras with known angular diameters. Comparison with pulsation theory shows that two of them (both with periods over 400d) are fundamental pulsators, while the others (all with periods of less than 400d) pulsate in a…
Vesta: Spin Pole, Size, and Shape from HST Images
Storrs, Alex D.; Thomas, Peter C.; Binzel, Richard P. +3 more
HST images obtained over an interval of 71 hr at a scale of 52 km/pixel have been used to determine the spin pole, size, and shape of Vesta. Several bright and dark surface features allow control point stereogrammetric measurement of spin pole orientation. An independent solution of spin pole and shape can be made from the limb and terminator coor…
Self-consistent Thermal Accretion Disk Corona Models for Compact Objects. II. Application to Cygnus X-1
Begelman, Mitchell C.; Wilms, Joern; Dove, James B. +1 more
We apply our self-consistent accretion disk corona (ADC) model, with two different geometries, to the broadband X-ray spectrum of the black hole candidate Cygnus X-1. As shown in a companion paper, models in which the Comptonizing medium is a slab surrounding the cold accretion disk cannot have a temperature higher than about 140 keV for optical d…
White Dwarfs in Globular Clusters: Hubble Space Telescope Observations of M4
Bond, Howard E.; Ibata, Rodrigo A.; Stetson, Peter B. +11 more
Using WFPC2 on the Hubble Space Telescope, we have isolated a sample of 258 white dwarfs (WDs) in the Galactic globular cluster M4. Fields at three radial distances from the cluster center were observed, and sizable WD populations were found in all three. The location of these WDs in the color-magnitude diagram, their mean mass of 0.51(+/-0.03) M<…
Dust and Recent Star Formation in the Core of NGC 5253
Meurer, Gerhardt R.; Calzetti, Daniela; Leitherer, Claus +4 more
Ultraviolet and optical narrow and broad band images of NGC 5253 obtained with the Hubble Space Telescope Wide Field and Planetary Camera 2 are used to derive the properties of the dust distribution and the recent star formation history of this metal-poor dwarf galaxy. Corrections for the effects of dust are important in the center of NGC 5253: du…
Dynamics of Broad Emission-Line Region in NGC 5548: Hydromagnetic Wind Model versus Observations
Korista, Kirk T.; Blandford, Roger D.; Bottorff, Mark +1 more
We analyze the results of long-term observations of the broad-line region (BLR) in the Seyfert 1 galaxy NGC 5548 and provide a critical comparison with the predictions of a hydromagnetically driven outflow model of Emmering, Blandford, & Shlosman. We use this model to generate a time series of C IV line profiles that have responded to a time-v…