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

Abstract

We present the results of a spectroscopic analysis of the Trapeziumcluster stars inside the Orion nebula. The rotational velocities wereobtained using the Fourier analysis method, and we found agreement withvalues derived by the usual method based on linewidth measurements. Therotational velocity derived for {\thetas}^{1} Ori C by thismethod is consistent with the variability of some of its spectralfeatures that have a period of 15.42 days. By means of the fit of H, HeI, and He II observed profiles with Fastwind synthetic profiles, stellarparameters and wind characteristics were derived. This methodology letus estimate the errors associated with these parameters, and we foundthat macroturbulence effects have to be included for a good fit to theHe I-II lines in the spectrum of {\thetas}^{1} Ori C. By means ofa very accurate study, oxygen abundances were derived for the threeB0.5V stars {\thetas}^{1} Ori A, D, and {\thetas}^{2} OriB. Final abundances are consistent with the nebular gas-phase resultspresented in Esteban et al. (2004) and are lower than those given byCunha {\amp} Lambert (1994). Our results suggest a lower dust depletionfactor of oxygen than previous estimations for the Orion nebula.