Astronomy & Astrophysics

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A&A 398, 647-661 (2003)
DOI: 10.1051/0004-6361:20021642

Rotation and differential rotation in field F- and G-type stars

A. Reiners and J. H. M. M. Schmitt

Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
(Received 2 October 2002 / Accepted 3 November 2002)

Abstract
We present a detailed study of rotation and differential rotation analyzing high resolution high S/N spectra of 142 F-, G- and early K-type field stars. Using Least Squares Deconvolution we obtain broadening profiles for our sample stars and use the Fourier transform method to determine projected rotational velocities $v\,\sin{i}$ . Distributions of rotational velocities and periods are studied in the HR-diagram. For a subsample of 32 stars of spectral type F0-G0 we derive the amount of differential rotation in terms of $\alpha = (\Omega_{\rm Equator} - \Omega_{\rm Pole})/\Omega_{\rm Equator}$ . We find evidence for differential rotation in ten of the 32 stars. Differential rotation seems to be more common in slower rotators, but deviations from rigid rotation are also found in some fast rotators. We search for correlations between differential rotation and parameters relevant for stellar activity and show indications against strong differential rotation in very active stars. We derive values of $\Delta P$ and $\Delta \Omega$ , which support a period dependence of differential rotation. Derived lap times $2\pi/\Delta \Omega$ are of the order of 20 d and contradict the assumption that constant lap times of the order of the solar one ( $\sim$ 130 d) are the rule in stars that are thought to harbour magnetic dynamos.

Key words: stars: rotation -- stars: late-type -- stars: activity

Offprint request: A. Reiners, areiners@hs.uni-hamburg.de

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