EDP Sciences
Free access
Volume 487, Number 1, August III 2008
Page(s) 323 - 327
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:200809935
Published online 16 June 2008

A&A 487, 323-327 (2008)
DOI: 10.1051/0004-6361:200809935

Research Note

Long-term monitoring of $\mathsf{\theta^1}$ Ori C: the spectroscopic orbit and an improved rotational period

O. Stahl1, G. Wade2, V. Petit3, B. Stober4, and L. Schanne5

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

Context. The young O-type star $\theta^1$ 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 $\theta^1$ 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 H$\alpha$ and HeII $\lambda4686$ lines.
Results. We find evidence for a secular change of the radial velocity of $\theta^1$ Ori C that is consistent with the published interferometric orbit. We refine the rotational period of $\theta^1$ Ori C and discuss the possibility of detecting period changes in the near future.

Key words: stars: individual: $\theta^1$ Ori C -- stars: emission-line, Be -- stars: variables: general -- stars: circumstellar matter -- stars: early-type

© ESO 2008