The following document lists the file abstract/RWATERS_OBDWARF.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
We propose to study the Infrared spectra of normal OB main sequence stars in order to investigate the structure of the outer layers of the photosphere and to determine the possible presence of a weak stellar wind. Ground-based observations of normal OB dwarfs demonstrate that IR Hydrogen lines (Br-alpha) can be strongly in emission while the H-alpha line is in absorption (Waters et al. 1993; Murdoch et al. 1994). Model calculations of the photospheric and wind emission of OB dwarfs indicate that, for very low mass loss rates, the Hydrogen recombination lines in the 4 to 40 micron wavelength range are still expected to show emission. This is due to the fact that the IR continuum of hot stars drops very rapidly with increasing wavelength, whereas the strength of the HI recombination lines decreases more slowly. This results in easily detectable emission lines in the 10-40 micron window. However in a recent paper by Murdoch el al. (1994) it is suggested that the IR emission may be due to a non-LTE effect in the outermost photospheric layers of hot stars. Both models predict different line strength ratios for the IR emission lines. Measurement of the strength of several Hydrogen lines in the SWS wavelength range will allow us to distinguish between both models. The study of the outer layers of the atmospheres of (hot) stars and of weak stellar winds can only be done with ISO.