The circumstellar environment of the Herbig Ae/Be stars. The case of AB Aurigae.

Abstract

The possibility that the near-infrared excess observed for AB Aur is due to free-free emission coming from a circumstellar H I region is investigated. The analysis of absorption lines (mainly of Fe II) present in IUE spectra shows that both the derived column densities and the excitation temperature (about 2000 K) indicate the presence of a conspicuous circumstellar H I region which could be responsible for the free-free emission although the contribution of dust is not excluded. The localization of the absorbing region is discussed in the framework of a stellar wind model and a tentative estimate of the mass loss rate is derived.