TOWARDS A SEISMIC MODEL OF THE DELTA-SCUTI STAR XX-PYXIDIS

Frequencies of 13 oscillation modes in the star XX Pyxidis (CD-247599) are accurately measured but for none of the modes the spherical harmo nic degree (I) is known. We present results of an attempt to construct the model whose lowe mode frequencies reproduce possibly close the ob servations. Models are constrained by the mean photometric and spectro scopic data for the star. However, the strongest constraint on the eff ective temperture is from the requirement that the modes excited in th e star fall into the range of the modes driven by the opacity mechanis m. Our models are built with the standard stellar evolution code allow ing no overshooting from the convective core. Effects of rotation are taken into account both in stellar evolution and in linear nonadiabati c oscillation calculations. Uniform rotation rate and conservation of the global angular momentum during evolution are assumed. We find seve ral distinct mode identifications and associated stellar models leadin g to frequency fits of similar quality. Determination of the l values for some of the modes could remove the ambiguity. None of the fits is satifactory: the mean departures exceed the mean observational frequen cy error by at least one order of magnitude. The fits could be improve d by means of adjusting model parameters that were kept fixed. However , such effort will be meaningful only after improving accuracy in calc ulation of the effects of rotation in oscillation frequencies.