Excitation Mechanism of O i Lines in Herbig Ae/Be Stars

Abstract

We have investigated the role of a few prominent excitation mechanisms viz. collisional excitation, recombination, continuum fluorescence, and Lyman beta fluorescence on the O i  line spectra in Herbig Ae/Be stars. The aim is to understand which of them is the central mechanism that explains the observed O i  line strengths. The study is based on an analysis of the observed optical spectra of 62 Herbig Ae/Be stars and near-infrared spectra of 17 Herbig Ae/Be stars. The strong correlation observed between the line fluxes of O i   λ 8446 and O i   λ 11287, as well as a high positive correlation between the line strengths of O i   λ 8446 and H α suggest that Lyman beta fluorescence is the dominant excitation mechanism for the formation of O i  emission lines in Herbig Ae/Be stars. Furthermore, from an analysis of the emission line fluxes of O i   λλ 7774, 8446, and comparing the line ratios with those predicted by theoretical models, we assessed the contribution of collisional excitation in the formation of O i  emission lines.