The aim of this proposal is to use infrared recombination lines of Hydrogen and Helium, as well as forbidden lines, to study the velocity field in Be star discs. Infrared spectroscopy of these discs has several advantadges over optical data. The IR lines are much easier to model than the optical Balmer or Paschen lines. Furthermore the IR lines have only weak photospheric components and so the correction for the underlying photospheric absorption lines introduces much less uncertainty in the emission contribution from the disc. Nothing is known about this rotational velocity field.
Recent observations indicate that some discs rotate faster than the underlying star.
The line strengths are sensitive probes of the density structure, both in the radial and in the vertical direction. In order to have sufficient constraints on models, it is important to observe many lines over a wide wavelength range and optical depth range, i.e. SWS is the ideal instrument to obtain such spectra. We also propose to investigate the high-level IR Hydrogen recombination lines in 'normal' B stars. Model calculations suggest that these lines are very senstive to the presence of small amounts of circumstellar gas, or to deviations from classical LTE model atmospheres. The recent discovery of Bralpha emission in tau Sco illustrates that normal B stars can have infrared Hydrogen recombination lines without having Balmer emission lines.