93 research outputs found
Multiwavelength optical observations of chromospherically active binary systems. III. High resolution echelle spectra from Ca II H&K to Ca II IRT
This is the third paper of a series aimed at studying the chromosphere of
active binary systems using the information provided for several optical
spectroscopic features. High resolution echelle spectra including all the
optical chromospheric activity indicators from the Ca II H & K to Ca II IRT
lines are analysed here for 16 systems. The chromospheric contribution in these
lines has been determined using the spectral subtraction technique. Very broad
wings have been found in the subtracted H_alpha profile of the very active star
HU Vir. These profiles are well matched using a two-component Gaussian fit
(narrow and broad) and the broad component can be interpreted as arising from
microflaring. Red-shifted absorption features in the H_alpha line have been
detected in several systems and excess emission in the blue wing of FG UMa was
also detected. These features indicate that several dynamical processes, or a
combination of them, may be involved. Using the E(H_alpha)/E(H_beta) ratio as a
diagnostic we have detected prominence-like extended material viewed off the
limb in many stars of the sample, and prominences viewed against the disk at
some orbital phases in the dwarfs OU Gem and BF Lyn. The He I D_3 line has been
detected as an absorption feature in mainly all the giants of the sample. Total
filling-in of the He I D_3, probably due to microflaring activity, is observed
in HU Vir. Self-absorption with red asymmetry is detected in the Ca II H & K
lines of the giants 12 Cam, FG UMa and BM CVn. All the stars analysed show
clear filled-in Ca II IRT lines or even notable emission reversal. The small
values of the E(8542)/E(8498) ratio we have found indicate Ca II IRT emission
arises from plage-like regions.Comment: Latex file with 38 pages, 25 figures. Full postscript (text and
figures) available at http://www.ucm.es/info/Astrof/pub_dmg.html To be
published in Astronomy & Astrophysics Supp.
Stellar activity in barium stars .1. Analysis of H-lines and K-lines CA-II-lines in 10 barium stars
High dispersion spectra have been obtained in order to study the activity level of ten barium stars by means of the Ca II H and K emission flux, looking for a relation between barium intensity index and activity. Absolute magnitudes obtained from the Wilson-Bappu relationship disagree, in some cases, with the magnitudes computed from parallaxes, but this fact is not due to barium nature. Total emission fluxes, F(H + K) or R_HK index, plotted versus effective temperature show a distribution similar to that of cool giant stars. The asymmetry of K emission line, [F(K_2ν)/F(K_2r)], has been analyzed in relation with effective temperature, in this sense barium stars behave as expected of late-type giants with the only exception of two stars
Barium and iron abundances in red giants
An intermediate-dispersion abundance analysis has been carried out on a sample of 21 barium and 14 comparison stars. The excess of barium over iron has been used as the most representative indicator of peculiarity. These excesses are higher in the peculiar stars than in the nonpeculiar stars. Particularly interesting is the case of HD 67447, included in the comparison stars, with an excess Ba/Fe abundance = 1.61, probably a new barium star. A trend indicating a possible anticorrelation between barium overabundance and metallicity favors the suggestion that the "barium strong" group is older than the "barium weak" one
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