Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...269..446s&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 269, no. 1-2, p. 446-456.
Astronomy and Astrophysics
Astrophysics
28
Dwarf Stars, Magnetoactivity, Stellar Convection, Stellar Envelopes, Stellar Activity, Stellar Rotation
Scientific paper
The magnetic activity in dwarf stars with shallow convective envelopes is addressed by studying the C II and soft X-ray surface flux densities in relation to the stellar rotation velocity. The C II emission from the acoustically heated basal atmospheric component increases with increasing T(eff) up to at least B-V about 0.25, reaching a level of about 8 x 10 exp 4 erg/sq cm/s for early F-type dwarf stars. A relationship between rotation rate and level of magnetic activity is found to extend down to at least B-V about 0.25, although the C II emission associated with the magnetic activity at B-V = 0.25 is suppressed by a factor of about 100 as compared to stars cooler than B-V about 0.60 with the same rotation rate. The suppression of activity is strongly color-dependent below B-V about 0.60, with the dynamo efficiency leveling off for cooler stars. The radiative losses associated with magnetic activity do not show a noticeable dependence on color in diagrams relating fluxes from chromosphere and corona for F-, G-, and K-type dwarf stars, suggesting comparable atmospheric structures for the magnetic component. The observed mean rotational velocities as a function of spectral type are shown to be consistent with the assumptions of (1) a reduced dynamo efficiency and (2) a comparable mechanism for angular momentum loss through a stellar wind for all magnetically active cool stars.
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