INVESTIGATING THE ORIGIN OF HOT GAS LINES IN HERBIG AE/BE STARS

Abstract

ABSTRACT We analyze high-resolution UV spectra of a small sample of Herbig Ae/Be stars (HAEBESs) in order to explore the origin of the T ∼ 105 K gas in these stars. The C iv λ λ1548, 1550 line luminosities are compared to nonsimultaneous accretion rate estimates for the objects showing C iv emission. We show that the correlation between L C iv and previously established for classical T Tauri stars (CTTSs) seems to extend into the HAEBE mass regime, although the large spread in literature and A V values makes the actual relationship highly uncertain. With the exception of DX Cha, we find no evidence for hot, optically thick winds in our HAEBE sample. All other objects showing clear doublet emission in C iv can be well described by a two-component (i.e., a single component for each doublet member) or four-component (i.e., two components for each doublet member) Gaussian emission line fit. The morphologies and peak-flux velocities of these lines suggest that they are formed in weak, optically thin stellar winds and not in an accretion flow, as is the case for the hot lines observed in CTTSs. The lack of strong outflow signatures and lack of evidence for line formation in accretion flows are consistent with the conclusion presented in our recent optical and He i λ10830 studies that the immediate circumstellar environments of HAEBESs, in general, are not scaled-up analogs of the immediate environments around CTTSs. The conclusions presented here for hot gas lines around HAEBESs should be verified with a larger sample of objects.