Long-term monitoring of Ori C: the spectroscopic orbit and an improved rotational period*
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
Accepted: 12 June 2008
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.
Key words: stars: individual: ϑ¹ Ori C / stars: emission-line, Be / stars: variables: general / stars: circumstellar matter / stars: early-type
© ESO, 2008