Detailed spectroscopic analysis of the Trapezium cluster stars inside the Orion nebula

Rotational velocities, stellar parameters, and oxygen abundances

¹ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain e-mail: ssimon@iac.es
² Isaac Newton Group of Telescopes, Apartado de Correos 321, 38700 Santa Cruz de la Palma, Tenerife, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, Avda. Astrofísico Francisco Sánchez, s/n, 38071 La Laguna, Spain
⁴ Instituto de Estructura de la Materia, CSIC, C/ Serrano 121, 28006 Madrid, Spain

Received: 15 March 2005
Accepted: 1 October 2005

Abstract

We present the results of a spectroscopic analysis of the Trapezium cluster stars inside the Orion nebula. The rotational velocities were obtained using the Fourier analysis method, and we found agreement with values derived by the usual method based on linewidth measurements. The rotational velocity derived for  Ori C by this method is consistent with the variability of some of its spectral features that have a period of 15.42 days. By means of the fit of , , and  observed profiles with Fastwind synthetic profiles, stellar parameters and wind characteristics were derived. This methodology let us estimate the errors associated with these parameters, and we found that macroturbulence effects have to be included for a good fit to the  lines in the spectrum of  Ori C.
By means of a very accurate study, oxygen abundances were derived for the three B0.5V stars  Ori A, D, and  Ori B. Final abundances are consistent with the nebular gas-phase results presented in Esteban et al. (2004) and are lower than those given by Cunha & Lambert (1994). Our results suggest a lower dust depletion factor of oxygen than previous estimations for the Orion nebula.