First signatures of strong differential rotation in A-type stars^*

¹ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany e-mail: areiners@hs.uni-hamburg.de
² Observatoire de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland e-mail: frederic.royer@obs.unige.ch
³ GEPI, CNRS UMR 8111, Observatoire de Paris, 5 place Janssen, 92195 Meudon cedex, France

Corresponding author: A. Reiners, areiners@hs.uni-hamburg.de

Received: 8 August 2003
Accepted: 6 November 2003

Abstract

We reanalyzed high quality spectra of 158 stars of spectral types A0–F1 and between 60 and 150 km s^-1. Using a Least Squares Deconvolution technique we extracted high  broadening profiles and determined the loci of the Fourier transform zeros q₁ and q₂ where the -ratio was high enough. The values of were redetermined and found to be consistent with the values derived by [CITE]. For 78 stars q₂ could be determined and the ratio was used as a shape parameter sensitive for solar-like differential rotation (Equator faster than Pole). 74 of the 78 stars have values of consistent with solid body rotation; in four of the 78 cases, values of are not consistent with rigid rotation. Although these stars may be binaries, none of the profiles shows signatures of a companion. The Fourier transforms do not indicate any distortions and the broadening profiles can be considered due to single objects. One of those candidates may be an extremely rapid rotator seen pole-on, but for the other three stars of spectral types as early as A6, differential rotation seems to be the most plausible explanation for the peculiar profiles.