A study of the infrared spectrum of psi Persei .1. A parameter study of the disc model

We report a parameter study of emission lines arising from a disc surrounding a Be star, using parameters appropriate to the Be star psi Per. We concentrate on the Hn line and on some IR recombination lines (Br alpha, Br gamma, Pf gamma, and HI 17-6). The model we use is a simple cone-like disc model, first proposed by Waters (1986). This model has been successful in explaining the continuum energy distribution of Be stars, and we now wish to study the emission line spectrum emerging from such a disc. We find that line shapes and ratios of line strengths are strongly dependent on the temperature structure of the disc. Infrared recombination lines will therefore be very useful in determining the physical state of the circumstellar envelopes of Be stars

THE HI INFRARED LINE SPECTRUM FOR BE STARS WITH LOW-DENSITY DISCS

We present theoretical H alpha and HI infrared recombination line calculations for low-density discs around B stars. Such a disc shows no visible emission in H alpha, while the HI IR recombination lines are in emission. This phenomenon has been found in the spectrum of the B0.2V star, tau Sco and could be simulated with a simple disc model. As an extension of that particular case we calculate the entire IR HI line spectrum of a normal B star surrounded by a low-density disc with a theoretical curve of growth for HI IR line fluxes, which we introduce as a tool for studying low-density discs. We find that IR emission lines may be detectable for densities up to about 10(-14) gcm(-3) which is a factor 10(2) - 10(3) lower than typically found in Be stars. For different spectral types, B0, B2, B5 and B8 we determined the density range for which emission is prominent in the IR recombination lines but not in Ha alpha

INFRARED-EMISSION LINES IN TAU-SCORPII - A POLE-ON BE STAR

We report the discovery of Bralpha and Brgamma emission in the infrared spectrum of the B0.2 V star tau Scorpii. The widths and strengths of the lines suggest that they are formed in a region of much higher density than is inferred from the UV resonance lines. This situation is similar to that found in Oe and Be stars. We show that the IR emission lines in tau Scorpii can be produced in a circumstellax disc of moderate density, without producing noticeable emission in Halpha. It is possible that a class of 'hidden' Be stars exists whose emission is prominent in the IR recombination lines but not in Halpha