Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006pasp..118.1112g&link_type=abstract
The Publications of the Astronomical Society of the Pacific, Volume 118, Issue 846, pp. 1112-1118.
Astronomy and Astrophysics
Astronomy
9
Line: Profiles, Stars: Activity, Stars: Late-Type, Stars: Rotation, Stars: Spots
Scientific paper
From two decades of high-resolution spectroscopic measurements of Arcturus (HR 5340, K2 III), we identify a 2 yr modulation in the velocity span of the bisector of the Fe I λ6252.57 line. It seems likely that this is the rotation period, and we deduce the equatorial rotation rate to be 1.8 +/- 0.3 km s-1, based on a radius of 25.4 Rsolar. From detailed Fourier analysis of the broadening and shapes of the spectral lines, we derive vsini = 1.5 +/- 0.3 km s-1 and a radial-tangential macroturbulence dispersion of 5.2 +/- 0.2 km s-1. The inclination of the rotation axis to the line of sight is then 58° +/- 25°. Considering the periods found by H.-J. Choi et al. from variations in the Ca II H and K line emission, we suggest that giant stars have two or three active longitudes and, therefore, that periods found from the modulation of magnetic features will be one-half or one-third of the rotation period.
Brown Kevin I. T.
Gray David F.
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