The Spectra of Be- and Ae-TYPE Stars Associated with Nebulosity

Abstract

An argument based on the relative rates of contractive and nuclear (hydrogen-burning) evolution for stars of masses 3 to 20 m0 enables an estimate to be made of the number of still-contracting stars of these masses within an observable distance of the sun. For example, within 1 kpc of the sun and 100 pc of the galactic plane one would expect there to be, somewhere in their contractive phase, about 18 stars that will in time reach the main sequence at types B2 and B3. A purely empirical attempt was made to identify some of these objects by examining in detail a list of 26 Be- and Ae-type stars that both lie in obscured regions and illuminate nearby nebulosity. The list contains such well-known variables as T Ori, AB Aur, RR Tau, Z CMa, and R Mon, as well as some newly found emission-line stars. In the course of the investigation two new variable nebulae were found. Two main types of stars were encountered: one with emission lines mainly of hydrogen plus absorption features due to a weak overlying shell; and another group with higher velocities of ejection, stronger emission lines, and line structure of the P Cygni type. Although it is entirely possible that this list of peculiar objects does contain examples of still-contracting stars of large mass, no convincing proof of this supposition could be found. The essential reason was that, although there are some striking spectroscopic peculiarities among the stars examined, at the dispersions employed in this investigation the peculiarities did not appear to be unique to this group: they may be found as well in stars that are not associated with nebulosity.