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A HST spectroscopic study of QSOs with intermediate redshift damped Lyalpha systems
Deharveng, Jean-Michel; Bergeron, Jacqueline; Le Brun, Vincent +1 more
We present HST spectra for a sample of six QSOs with intermediate redshift (z_ale 1.) damped Lyalpha systems. These observations aim at measuring the Hi column density and detect metal lines in order to investigate the metal enrichment of the gas, as well as the presence of neutral species, molecules and dust. All systems selected on the basis of …
Metal-rich globular clusters in the galactic disk: new age determinations and the relation to halo clusters
Salaris, M.; Weiss, A.
New age determinations of the galactic disk globular clusters 47 Tuc, M 71 and NGC 6352 have been performed with our up-to-date alpha -enhanced stellar models. We find that all three clusters are about 9.2 Gyr old and therefore coeval with the oldest disk white dwarfs. Several arguments are presented which indicate that the initial helium content …
The distribution of nearby stars in phase space mapped by Hipparcos. I. The potential well and local dynamical mass
Pichon, C.; Creze, M.; Chereul, E. +1 more
Hipparcos data provide the first, volume limited and absolute magnitude limited homogeneous tracer of stellar density and velocity distributions in the solar neighbourhood. The density of A-type stars more luminous than M_v=2. 5 can be accurately mapped within a sphere of 125 pc radius, while proper motions in galactic latitude provide the vertica…
The TYCHO Reference Catalogue
Makarov, V. V.; Lindegren, L.; Bastian, U. +5 more
The Tycho Reference Catalogue\ (TRC) contains high-quality positions and proper motions for 990 182\ stars of the Tycho Catalogue. The proper motions were derived from Tycho positions and Astrographic Catalogue\ positions reduced to the Hipparcos system. The median accuracy of the TRC position components is 40 mas at J1991.25. The median precision…
Broadening of SI VIII lines observed in the solar polar coronal holes
Doyle, J. G.; Wilhelm, K.; Teriaca, L. +1 more
We study the variation of the line width and electron density as a function of height above two coronal holes from forbidden spectral lines of Si viii. The spectra were obtained with the Solar Ultraviolet Measurements of Emitted Radiation spectrometer flown on the Solar and Heliospheric Observatory spacecraft. The observations concentrate on the d…
Mixing processes during the evolution of red giants with moderate metal deficiencies: the role of molecular-weight barriers
Wallerstein, George; Charbonnel, Corinne; Brown, Jeffery A.
We have assembled accurate abundance data for Li, C, and N as well as the (12}C/({13)) C ratio for five field giants with [Fe/H] =~ - 0.6 including Arcturus and two stars in the globular cluster 47 Tuc. Using their very precise Mbol values obtained from HIPPARCOS parallaxes, we can place them into an evolutionary sequence. The sequence …
An analytic solar magnetic field model
McKenzie, J. F.; Banaszkiewicz, M.; Axford, W. I.
We describe a simple analytic model for the magnetic field in the solar corona and interplanetary space which is appropriate to solar minimum conditions. The model combines an azimuthal current sheet in the equatorial plane with an axisymmetric multipole field representing the internal magnetic field of the Sun. The radial component of the field f…
The absolute magnitudes of RR Lyraes from HIPPARCOS parallaxes and proper motions
Garrido, R.; Evans, D. W.; Solano, E. +5 more
We have used HIPPARCOS proper motions and the method of Statistical Parallax to estimate the absolute magnitude of RR Lyrae stars. In addition we used the HIPPARCOS parallax of RR Lyrae itself to determine it's absolute magnitude. These two results are in excellent agreement with each other and give a zero-point for the RR Lyrae M_v,[Fe/H] relatio…
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…
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…