The accreting circumstellar gas envelope of HD 176386 a young star inthe R Coronae Austrinae star formation region.

Abstract

We report recent and archival IUE observations of the Herbig Be star HD 176386. We find accreting gas toward the star with velocities up to +300 km s^-1 in C IV and Si IV. Detection of these species in a B9.5 star is consistent with collisional ionization of the accreting gas to temperatures in excess of the stellar T_eff. The IUE data also provide evidence for the presence of discrete absorption features similar to those observed in optical and UV spectra of β Pic. The accreting gas column densities, and maximum accretion velocity are intermediate between those seen in younger Herbig Ae/Be stars such as HR 5999 and HD 45677 and field systems such as β Pic and 51 Oph. These data suggest a gradual transition from the optically thick (continuum), high mass accretion rates seen in the younger Herbig Ae/Be stars to optically thin accretion typical of systems such as β Pic, and that the time scale for such a transition for a B9.5 star appears to be 1.5 ≤ t ≤ 2.8 Myr.