Research Note

Long-term monitoring of Ori C: the spectroscopic orbit and an improved rotational period^*

¹ ZAH, Landessternwarte Königstuhl, 69117 Heidelberg, Germany e-mail: O.Stahl@lsw.uni-heidelberg.de
² Dept. of Physics, Royal Military College of Canada, PO Box 17000, Station Forces, Kingston, ON, K7K 7B4, Canada
³ Département de physique, génie physique et optique, Centre de recherche en astrophysique du Québec, Université Laval, Québec (QC) G1K 7P4, Canada
⁴ Nelkenweg 14, 66791 Glan-Münchweiler, Germany
⁵ Hohlstraße 19, 66333 Völklingen-Ludweiler, Germany

Received: 9 April 2008
Accepted: 12 June 2008

Abstract

Context. The young O-type star  Ori C, the brightest star of the Trapezium cluster in Orion, is one of only two known magnetic rotators among the O stars. However, not all spectroscopic variations of this star can be explained by the magnetic rotator model. We present results from a long-term monitoring to study these unexplained variations and to improve the stellar rotational period.

Aims. We want to study long-term trends of the radial velocity of  Ori C, to search for unusual changes, to improve the established rotational period and to check for possible period changes.

Methods. We combine a large set of published spectroscopic data with new observations and analyze the spectra in a homogeneous way. We study the radial velocity from selected photo-spheric lines and determine the equivalent width of the Hα and Heii  lines.

Results. We find evidence for a secular change of the radial velocity of  Ori C that is consistent with the published interferometric orbit. We refine the rotational period of  Ori C and discuss the possibility of detecting period changes in the near future.