Properties of the Be stars in the field of the Small Magellanic Cloud cluster NGC 330.

The blue globular cluster NGC 330 in the Small Magellanic Cloud is one of the few SMC clusters to be rich in young luminous stars. The incidence of Be stars in the cluster is known to be high (Feast 1972MNRAS.159..113F; Grebel et al. 1992A&A...254L...5G). Medium resolution, high signal-to-noise (S/N) optical spectra of many of the brightest blue stars in the cluster have been obtained, and for some of the stars high resolution, high S/N spectra have also been acquired. New Johnson U and B photometry has also been obtained. Spectroscopy shows that even stars that were not classified as Be photometrically do have emission at least in Hα, so that the vast majority of the early B-type, non-supergiant stars in the cluster are Be (13 stars out of 14 in our sample). The physical parameters (effective temperature, surface gravity) of the stars have been determined, and their emission properties (full-width-half-maximum, emission equivalent width of the Balmer lines) have been investigated. The Hα emission flux appears to be proportional to the value of the FWHM, and, by inference, to that of vsini. All Be stars have similar, single-peaked Hα emission profiles, regardless of emission strength and stellar vsini. This is in some sense an unexpected result, and may be taken to indicate that the extension of the discs surrounding the stars, whence the Hα emission is supposed to arise, depends on the rotational velocity of the stars (which would explain the absence of broad double peaks). The possible absence of double-peaked profiles of any separation, if confirmed, may also indicate that the Be stars in NGC 330 are observed under roughly the same inclination angle, or that they are all surrounded by extended and optically thick discs.