Letter to the Editor

Strong latitudinal shear in the shallow convection zone of a rapidly rotating A-star^*

¹ Astronomy Department, University of California, Berkeley, CA 94720, USA e-mail: areiners@astron.berkeley.edu
² Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany e-mail: jschmitt@hs.uni-hamburg.de
³ Institut für Theoretische Physik und Astrophysik, Leibnizstrasse 15, 24098 Kiel, Germany e-mail: mhuensch@astrophysik.uni-kiel.de
⁴ Astrophysikalisches Institut Jena, Schillergäßchen 2-3, 07745 Jena, Germany e-mail: marc@astro.uni-jena.de

Received: 2 November 2004
Accepted: 9 December 2004

Abstract

We have derived the mean broadening profile of the star V 102 in the region of the open cluster IC 4665 from high resolution spectroscopy. At a projected equatorial rotation velocity of  km s^-1 we find strong deviation from classical rotation. We discuss several scenarios, the most plausible being strong differential rotation in latitudinal direction. For this scenario we find a difference in angular velocity of  rad d^-1 (. From the Hα line we derive a spectral type of A9 and support photometric measurements classifying IC 4665 V 102 as a non-member of IC 4665. At such early spectral type this is the strongest case of differential rotation observed so far. Together with three similar stars, IC 4665 V 102 seems to form a new class of objects that exhibit extreme latitudinal shear in a very shallow convective envelope.