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Quantitative spectroscopy of Wolf-Rayet stars in HD97950 and R136a - the cores of giant HII regions
Crowther, P. A.; Dessart, Luc
We present quantitative analyses of Wolf-Rayet stars in the cores of two giant Hii regions - HD97950 in NGC3603 and R136a in 30 Doradus - based on archive Hubble Space Telescope (HST) spectroscopy. We confirm previous WN6h+abs classifications for components A1, B and C in HD97950, while classifications for R136a1-3 are revised from O3If^*/WN6 to W…
Large-scale coronal heating by the small-scale magnetic field of the Sun
Schrijver, C. J.; Tarbell, T. D.; Shine, R. A. +6 more
Magnetic fields play a crucial role in heating the outer atmospheres of the Sun and Sun-like stars, but the mechanisms by which magnetic energy in the photosphere is converted to thermal energy in the corona remain unclear. Observations show that magnetic fields emerge onto the solar surface as bipolar regions with a broad range of length scales. …
Detection of Abundant CO2 Ice in the Quiescent Dark Cloud Medium toward Elias 16
de Graauw, Th.; Prusti, T.; van Dishoeck, E. F. +9 more
We report the first detection of solid carbon dioxide (CO2) in quiescent regions of a dark cloud in the solar neighborhood, a result that has important implications for models of ice formation and evolution in the interstellar medium. The K-type field star Elias 16 was previously known to display solid-state absorption features of H
Measurement of the electron temperature gradient in a solar coronal hole
Wilhelm, K.; Fludra, A.; Lemaire, P. +3 more
It has long been established that the high speed solar wind streams observed at 1 A.U. originate from the coronal hole regions of the Sun. Theoretical modelling of the acceleration mechanism depends critically on the value of the maximum of temperature existing close to the Sun. Measurements of the temperature in coronal holes prior to SOHO are un…
Testing the White Dwarf Mass-Radius Relation with HIPPARCOS
Provencal, J. L.; Shipman, H. L.; Thejll, P. +1 more
We present the Hipparcos parallaxes and resulting radii for 10 white dwarfs in visual binaries or common proper-motion systems and 11 field white dwarfs. For bright stars, Hipparcos parallaxes have uncertainties approaching 1 mas and are thus considerably more accurate than earlier ground-based parallaxes. Overall, our results support the predicti…
The Slope of the Cluster Elliptical Red Sequence: A Probe of Cluster Evolution
Yee, H. K. C.; Kodama, Tadayuki; Gladders, Michael D. +1 more
The current formation models for cluster elliptical galaxies, which incorporate a mechanism for the metallicity enhancement of massive elliptical galaxies, predict a change in the observed slope of the red sequence of elliptical galaxies as a function of redshift. This change occurs primarily because the metal-rich galaxies become redder faster th…
Interstellar and Inner Source Pickup Ions Observed with SWICS on ULYSSES
Gloeckler, George; Geiss, Johannes
Many species of pickup ions, both of interstellar origin and from an inner, distributed source have been discovered using data from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses. Velocity distribution functions of these ions were measured for the first time over heliocentric distances between 1.35 and 5.4 AU, both at high and low …
High-redshift galaxies in the Hubble Deep Field - II. Colours and number counts
Ferguson, Henry C.; Madau, Piero; Zamorani, Gianni +2 more
We discuss the deep galaxy counts from the Hubble Deep Field (HDF) imaging survey. At faint magnitudes, the slope of the differential number-magnitude relation is flatter than 0.2 in all four HDF bandpasses. In the ultraviolet, a fluctuation analysis shows that the flattening observed below U_300~26 mag is not caused by incompleteness and is more …
Crystalline silicates in planetary nebulae with [WC] central stars
de Graauw, Th.; Waters, L. B. F. M.; Pottasch, S. R. +6 more
We present ISO-SWS spectroscopy of the cool dusty envelopes surrounding two Planetary Nebulae with [WC] central stars, BD+30 3639 and He 2-113. The lambda < 15 mu m region is dominated by a rising continuum with prominent emission from C-rich dust (PAHs), while the long wavelength part shows narrow solid state features from crystalline silicate…
The ACT Reference Catalog
Urban, S. E.; Wycoff, G. L.; Corbin, T. E.
The US Naval Observatory has completed the compilation of the ACT Reference Catalog, containing 988,758 stars covering the entire sky. The motivation behind the ACT was to provide accurate proper motions for the majority of the stars in the Tycho Catalogue. To do this, positions from new reductions of the Astrographic Catalogue (AC 2000) were comb…