Long-term monitoring of theta1OriC: the spectroscopic orbit and an improved rotational period

O. Stahl (1), G. Wade (2), V. Petit (3), B. Stober (4), L. Schanne (5)

1 - ZAH, Landessternwarte Koenigstuhl, 69117 Heidelberg, Germany
2 - Dept. of Physics, Royal Military College of Canada, PO Box 17000, Station Forces, Kingston, ON, Canada K7K 7B4
3 - Departement de physique, genie physique et optique, Centre de recherche en astrophysique du Quebec, Universite Laval, Quebec (QC) G1K 7P4
4 - Nelkenweg 14, 66791 Glan-Muenchweiler, Germany
5 - Hohlstrasse 19, 66333 Voelklingen-Ludweiler, Germany

The young O-type star theta1OriC, 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. We want to study long-term trends of the radial velocity of theta1OriC, to search for unusual changes, to improve the established rotational period and to check for possible period changes. 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 Halpha and HeII4686 lines. We find evidence for a secular change of the radial velocity of theta1OriC that is consistent with the published interferometric orbit. We refine the rotational period of theta1OriC and discuss the possibility of detecting period changes in the near future.

Reference: Astron. Astrophys. (accepted)
Status: Manuscript has been accepted

Weblink: http://de.arxiv.org/abs/0805.0701


Email: O.Stahl@lsw.uni-heidelberg.de