A study of bright southern slowly pulsating B stars - III. Mode identification for singly-periodic targets in spectroscopy

We present the results of the mode identification for a sample of 7 bright southern slowly pulsating B stars showing one pulsation frequency in the.. 413 nm Si II profiles. We combined the results from ( 1) the method of photometric amplitudes; ( 2) the moment method; and ( 3) the amplitude and phase variation across the profile to search for the l and m values of the modes best fitting the data. It is the first time that the applicability of these techniques is tested to a sample of main-sequence g-mode pulsators. Combining the moment method with the amplitude and phase variations across the observed line profile gives an improvement in spectroscopic identification of low degree l g-mode pulsations. Using the variations of the higher order even moments [v(4)] and [v(6)] of the moment method solutions can also help. For HD181558, HD24587, HD140873 and HD177863, the photometric and spectroscopic results are compatible and point towards ( l, m) = ( 1, + 1) sectoral modes. For HD215573, HD53921 and HD92287, the results are inconclusive. Our proposed methodology for mode identification is also applicable to gamma Doradus stars.