METALLIC LINE-PROFILES OF THE A0-V-STAR VEGA

High-dispersion (2.4 angstrom mm-1) ultrahigh signal-to-noise ratio Reticon spectra of Vega have been obtained with the coude spectrograph of the 1.2 m telescope of the Dominion Astrophysical Observatory. A mean signal-to-noise ratio of 2500 over the spectral region lambda-lambda-3825-5435 has been achieved. Examination of the line profiles has confirmed the presence of two distinct types of profiles which had been previously seen in IIIa-J and lower signal-to-noise ratio Reticon spectra. The profiles of the strong lines are essentially classical rotational profiles with enhanced wings. The weak lines are clearly flat-bottomed resulting in a trapezoidal appearance. Vega is not unique in this respect as 10 Tri, nu Cap, beta PsA, and possibly several other stars with spectral types near A0, have similar line profiles. A few possible theoretical explanations are presented. For example, these profiles might be the result of a rapidly rotating star seen nearly pole-on.