Towards a seismic model of the δ Scuti star XX Pyxidis

Frequencies of 13 oscillation modes in the star XX Pyxidis (CD–24 7599) are accurately measured but for none of the modes the spherical harmonic degree (l) is known. We present results of an attempt to construct the model whose low–l mode frequencies reproduce possibly close the observations. Models are constrained by the mean photometric and spectroscopic data for the star. However, the strongest constraint on the effective temperture is from the requirement that the modes excited in the star fall into the range of the modes driven by the opacity mechanism. Our models are built with the standard stellar evolution code allowing no overshooting from the convective core. Effects of rotation are taken into account both in stellar evolution and in linear nonadiabatic oscillation calculations. Uniform rotation rate and conservation of the global angular momentum during evolution are assumed. We find several distinct mode identifications and associated stellar models leading 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 frequency error by at least one order of magnitude. The fits could be improved by means of adjusting model parameters that were kept fixed. However, such effort will be meaningful only after improving accuracy in calculation of the effects of rotation in oscillation frequencies.