ON THE NATURE OF THE RADIAL-VELOCITY VARIABILITY OF ALDEBARAN - A SEARCH FOR SPECTRAL-LINE BISECTOR VARIATIONS

The shape of the Ti I 6303.8-Angstrom spectral line of Aldebaran as me asured by the line bisector was investigated using high signal-to-nois e ratio, high-resolution data. The goal of this study was to understan d the nature of the 643-d period in the radial velocity for this star reported by Hatzes & Cochran. Variations in the line bisector with the radial velocity period would provide strong evidence in support of ro tational modulation or stellar pulsations as the cause of the 643-d pe riod. A lack of any bisector variability at this period would support the planet hypothesis. Variations in the line asymmetries are found wi th a period of 49.93 d. These variations are uncorrelated with the 643 -d period found previously in the radial velocity measurements. It is demonstrated that this 50-d period is consistent with an m = 4 non-rad ial sectoral g-mode oscillation. The lack of spectral variability with the radial velocity period of 643 d may provide strong evidence in su pport of the hypothesis that this variability stems from the reflex mo tion of the central star due to a planetary companion having a mass of 11 Jupiter masses. However, this long-period variability may still be the result of a low-order (m = 2) pulsation mode as these would cause bisector variations of less than the error measurement.