Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991apj...380..200s&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 380, Oct. 10, 1991, p. 200-207.
Astronomy and Astrophysics
Astrophysics
60
A Stars, Chromosphere, F Stars, Stellar Activity, Stellar Winds, Ultraviolet Spectra, Dwarf Stars, Early Stars, Iue
Scientific paper
Results are reported from a search for an upper boundary for the onset of main-sequence star activity based on a quest for high-temperature UV line emission in a large collection of IUE spectra. It is shown that strong chromospheric emission is common among early F dwarf and subgiant stars. At its brightest, the emission is equal to that of the most active solar-type stars and is exceeded only by that of the spotted RS CVn and BY Dra variables. It is suggested that the emission from the main-sequence stars reaches a peak near B-V = 0.28, in the vicinity of spectral type F0 V, before it declines to lower flux levels among the late A stars. Emission is seen in some dwarf stars as early as B-V = 0.25. It is demonstrated that the C II emission of stars earlier than the spectral type F5 is uncorrelated with rotation. Previous findings that the coronal X-ray:chromospheric UV flux ratio is lower for stars earlier than spectral type F5 than for those later than F5 are confirmed.
Landsman Wayne
Simon Theodore
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