Search Publications
A high deuterium abundance at redshift z = 0.7
Ferlet, R.; Vidal-Madjar, A.; Lemoine, M. +4 more
Of the light elements, the primordial abundance of deuterium relative to hydrogen, (D/H)p, provides the most sensitive diagnostic for the cosmological mass density parameter, ΩB. Recent high-redshift D/H measurements are highly discrepant, although this may reflect observational uncertainties,. The larger primordial D/H value…
The EXOSAT Data on GX 339-4: Further Evidence for an ``Intermediate'' State
Méndez, Mariano; van der Klis, Michiel
We have studied the fast timing and spectral behavior of the black hole candidate (BHC) GX 339-4 using all 1-20 keV EXOSAT ME data: the 1983 July, 1984 March, 1984 May, and 1985 April observations. In 1985 April, GX 339-4 was in a weak low state (0.03 × 10-9 ergs cm-2 s-1, 2-10 keV). The X-ray spectrum was a hard p…
Quasar Absorbing Galaxies at z <~ 1: Deep Imaging and Spectroscopy in the Field of 3C 336
Dickinson, Mark; Steidel, Charles C.; Sembach, Kenneth R. +2 more
We present very deep WFPC2 images and FOS spectroscopy from the Hubble Space Telescope (HST) together with numerous supporting ground-based observations of the field of the quasar 3C 336 (zem = 0.927). The observations are designed to investigate the nature of galaxies producing metal-line absorption systems in the spectrum of the QSO. …
Infrared Spectroscopy of Dust in the Diffuse Interstellar Medium toward Cygnus OB2 No. 12
de Graauw, Th.; Prusti, T.; van Dishoeck, E. F. +7 more
Observations made with the short-wavelength spectrometer of the Infrared Space Observatory are used to investigate the composition of interstellar dust in the line of sight to Cygnus OB2 No. 12, commonly taken as representative of the diffuse (low-density) interstellar medium. Results are compared with data for the Galactic center source Sgr A*. N…
The Dependence of the Circumnuclear Coma Structure on the Properties of the Nucleus
Rodionov, A. V.; Crifo, J. F.
A new step of development of the 3-D circumnuclear coma (“CNC”) model described in Crifoet al.(1995) is presented: now the gas and dust production are computed from an explicit dusty-ice sublimation model and a realistic dust mass spectrum is used. For the first time, (1) a clear distinction is made betweennucleus active area fraction gandactive s…
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…