SPECTRAL-LINE PROFILE VARIATIONS IN THE GAMMA-DORADUS VARIABLE HD-164615 - NONRADIAL PULSATIONS VERSUS STAR-SPOTS

High-resolution spectral data of the Fe coproduct 5318 Angstrom line i n the gamma Doradus star HD 164615 are presented. These show systemati c changes in the spectral lineshapes with the photometric period of 0. 8133 d which are modelled using either non-radial pulsations or cool s tar-spots. The non-radial modes that can fit the lineshape changes hav e m degree of 2-4. However, only the m = 2 mode seems to be consistent with the amplitude of the radial velocity variations measured for thi s star. The star-spot model, although it can qualitatively fit the lin eshape changes, is excluded as a possible hypothesis on the basis of ( 1) poorer fits to the observed spectral line profiles, (2) an inabilit y to account for the large changes in the spectral linewidth as a func tion of phase, (3) a predicted radial velocity curve that looks qualit atively different from the observed one, and (4) a predicted photometr ic curve that is a factor of 5 larger than the observed light curve (a nd with the wrong qualitative shape). Finally, a 'Doppler image' (assu ming cool spots) derived from a sequence of synthetic line profiles ha ving non-radial pulsations results in an image that is almost identica l to the Doppler image derived for HD 164615. These results provide st rong evidence that non-radial pulsations are indeed the explanation fo r the variability of HD 164615 as well as the other gamma Dor variable s.