HD 135344B: a young star has reached its rotational limit^⋆

¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: amueller@mpia.de
³ Johns Hopkins University, Dept. of Physics and Astronomy, 3701 San Martin drive, Baltimore, MD 21210, USA

Received: 16 February 2011
Accepted: 23 March 2011

Abstract

Aims. We search for periodic variations in the radial velocity of the young Herbig star HD 135344B to determine a rotation period.

Methods. We analyze 44 high-resolution optical spectra taken over a time period of 151 days. The spectra were acquired with FEROS at the 2.2 m MPG/ESO telescope in La Silla. The stellar parameters of HD 135344B are determined by fitting synthetic spectra to the stellar spectrum. To obtain radial velocity measurements, the stellar spectra are cross-correlated with a theoretical template computed from determined stellar parameters.

Results. We report the first direct measurement of the rotation period of a Herbig star from radial velocity measurements. The rotation period is found to be 0.16 d (3.9 h), which makes HD 135344B a rapid rotator at or close to its break-up velocity. The rapid rotation could explain some of the properties of the circumstellar environment of HD 135344B such as an inner disk with properties (composition, inclination) that differ significantly from the outer disk.