Spectroscopic evidence of sporadic gas accretion onto the herbig Ae stars with non-periodic algol-type minima

Abstract
We present the results of simultaneous spectroscopic and photometric observations for six isolated Herbig Ae stars with non-periodic Algol-like minima: UX Ori, BF Ori, CQ Tau, SV Cep, VX Gas, and WW Vul. In all cases the Ha line has the profile typical for axially symmetric accretion. In the spectra of five stars (CQ Tau is the exception) the strong He I 5876 Å line has been observed in absorption which is not typical of normal A stars. In three cases: UX Ori, VX Cas, and WW Vul, variability of this line is found. We did not observe any correlation between the strength of this line and the brightness of the stars. These observational facts are considered as evidence for gas accretion, which is probably an important property of young stars with non-periodic Algol-type minima.

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