IV. Mode identifications and pulsation modelling

This paper examines the mode identification and presents pulsation models for FG Vir, for which 24 frequen- cies have been detected. Histograms of the frequency spacings show peaks which are identified with adjacent radial orders and rotational splitting. Pulsational ' values are deduced for eight modes by com- paring the observed photometric phase lags between v and y variations with calculated values. The dominant pulsation mode at 12.72 c/d can be identified with ' =1 , while the 12.15 c/d mode is the radial fundamental. These results are in agreement with identifications published by Viskum et al. (1998). Based on the observational mode identifications and the Hip- parcos distance, new models were computed with the constraint that the mode at 12.15 c/d is the radial fundamental mode. It is shown that with standard opacities, models in the appropriate Te , log L and log g ranges cannot reproduce the identification in the literature of 23.40 c/d as the third radial overtone. How- ever, we show that observationally an ' = 1 (rather than radial) identification is equally probable. A large number of pulsation models were computed for FG Vir. A comparison between the observed frequencies and mode identifications and pulsation models leads to a mean den- sity of = =0 :156 0:002 depending on the opacity and chemical composition choice and on the possible overshooting from the convective core. The models also correctly predict the observed region of instability between 9 and 34 c/d. The effect of rotational coupling on the pulsation frequen- cies is estimated.