Search Publications
Accretion shocks in T Tauri stars: diagnosis via semiforbidden ultraviolet line ratios
Lamzin, S. A.; Gomez de Castro, Ana I.
Numerical calculations of the structure of accretion shocks in T Tauri stars (TTSs) indicate that the C III]1909, O III]1661+1666 and Si III]1892 ultraviolet lines should have comparable intensities. We show how the density and the velocity of the accreted gas can be derived from these line ratios. We also indicate how these parameters can be used…
Consequences of HIPPARCOS parallaxes for stellar evolutionary models. Three Hyades binaries: V 818 Tauri, 51 Tauri, and theta (2) Tauri
Valls-Gabaud, D.; Lastennet, E.; Oblak, E. +1 more
Three binary systems in the Hyades open cluster (51 Tau, V818 Tau, and theta (2) Tau), with known {metallicity} and good Johnson photometric data are used to test the validity of three independent sets of stellar evolutionary tracks. A statistical method is described and applied to the colour-magnitude diagram of the six selected components, givin…
The Effective Temperature of Arcturus
Lynas-Gray, A. E.; Griffin, R. E. M.
We construct an empirical energy distribution for Arcturus from published scans, integrate it to obtain the total flux, and combine the latter with precise interferometric measurements of the limb-darkened angular diameter to derive the effective temperature. We conclude that the best value that can be derived within the framework of the associate…
Dust in R71: first detection of crystalline silicates in the LMC
Waters, L. B. F. M.; Morris, P. W.; de Koter, A. +3 more
We present infrared spectroscopy taken with the Infrared Space Observatory (ISO) of the Luminous Blue Variable (LBV) R71 in the Large Magellanic Cloud (LMC). The spectrum shows clear evidence for the presence of crystalline olivine at 23.5 mu m. This is the first detection of circumstellar crystalline silicates outside our galaxy. In addition, we …
Far-Ultraviolet Space Telescope Imaging Spectrometer Spectra of the White Dwarf REJ 1032+532. I. Interstellar Line of Sight
Barstow, M. A.; Bruhweiler, F. C.; Holberg, J. B. +1 more
An 1150-1725 Å echelle spectrum of the hot DA white dwarf REJ 1032+532, recently obtained with the Space Telescope Imaging Spectrometer E140M grating, reveals numerous stellar and interstellar lines. The interstellar column densities and abundances of C, N, O, Si, and S relative to the directly measured H column are determined for this particular …
Composition Variations in the Solar Corona and Solar Wind
Raymond, J. C.
Order of magnitude variations in relative elemental abundances are observed in the solar corona and solar wind. The instruments aboard SOHO make it possible to explore these variations in detail to determine whether they arise near the solar surface or higher in the corona. A substantial enhancement of low First Ionization Potential (FIP) elements…
Evidence of a solar origin for pressure balance structures in the high-latitude solar wind
Reisenfeld, D. B.; McComas, D. J.; Steinberg, J. T.
Ulysses observations of the high-latitude solar wind have shown that on time scales of < 1 day, the polar wind is dominated by pressure balance structures (PBSs). Fluctuations of the plasma beta within PBSs appear to be strongly correlated with fluctuations in the helium abundance. The correlation occurs in both the northern and southern hemisp…
The Kinematics and Origin of smr Stars
Grenon, M.
Ages and kinematics are revised for SMR stars ([M/H] >+0.30) common to NLTT and HIPPARCOS catalogues. The origin of MR to SMR stars appears heterogeneous: part of them, of intermediate age, were formed few kpc inside the solar orbit, from slowly enriched gas, whereas the oldest SMRs were born early, closer to the galactic center where the metal…
Dust in the Ionized Medium of the Galaxy: GHRS Measurements of AL III and S III
Savage, Blair D.; Howk, J. Christopher
We present interstellar absorption-line measurements of the ions S III and Al III toward the stars β1 Sco, µ Col, ξ Per, ζ Oph, ρ Leo, and HD 18100 using archival data from the Goddard High-Resolution Spectrograph on board the Hubble Space Telescope. The ions Al III and S III trace heavily depleted and nondepleted elements, respec…
Evolution of X-ray activity and rotation on G-K giants
Gondoin, P.
The recent availability of stellar parallaxes provided by the Hipparcos star catalogue (ESA 1997) enables an accurate determination of the positions of single field giants in a theoretical H-R diagram and a reliable estimate of their masses. The present study combines these new astrometric data with previously published X-ray fluxes and rotational…