Rotation and Stellar Activity of the Stars of the α Centauri Triple Star System

Details Rotation and Stellar Activity of the Stars of the α Centauri Triple Star System Rotation and Stellar Activity of the Stars of the α Centauri Triple Star System

Jan 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aas...18912004j&link_type=abstract

American Astronomical Society, 189th AAS Meeting, late abstracts, #120.04; Bulletin of the American Astronomical, Vol. 29, p. 73

Astronomy and Astrophysics

Astronomy

5

Scientific paper

At a distance of 4.3 LY, the alpha Cen triple star system is the nearest neighbor to the Sun. The system consists of the bright G2V and K2V binary pair having an orbital period of 81.2 yrs. These stars are designated as alpha Cen A and B, respectively. The third star, Proxima Cen (alpha Cen C; V645 Cen; Gl 551), is about 1400 AU from the alpha Cen AB; it has a spectral type of dM5e and has frequent flares. The stars have well determined physical properties because they are nearby and well studied. The isochronal evolutionary age of the stars is 5-6Gyrs. The alpha Cen star system is a great importance to magnetic dynamo theory because it contains three coeval stars with different convective zone depths, ranging from shallow for alpha Cen A to fully convective for Proxima. One quantity, not well determined yet vital to understanding the magnetic behavior of these stars, is the rotation period. During May-August 1995, alpha Cen A,B, and C were observed about twice a week with the IUE \ Satellite. The chief aim of this study is obtain the rotation periods of the stars by using the chromospheric and transition-region emission line features, arising from active regions on the stars, as markers for measuring rotation. A rotation period of Prot = 30.1+/-1.5 days was found for Proxima Cen (see BAAS,28,942). For alpha Cen B, the rotation period is Prot = 36.9+/-0.5 days. The rotation period for alpha Cen A is more difficult to determine because the UV \ emission features are relatively weak and the observed variations are small, but there seems to be evidence of a period of Prot = 23({) +5}_{-2} days. The period determination of alpha Cen A is still tentative, while the periods for alpha Cen B and C appear well determined. In this paper we discuss the implications of these periods in terms of magnetic braking and stellar dynamo theory. This study is supported by NASA grant NAG 5-2160 and NSF grant AST-9315365, which we gratefully acknowledge.

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