The two hybrid B-type pulsators: Nu Eridani and 12 Lacertae

TL;DR

This study models the hybrid pulsators Nu Eridani and 12 Lacertae, analyzing their oscillation spectra, internal rotation, and mode excitation, highlighting uncertainties in opacity data and their impact on stellar modeling.

Contribution

The paper presents seismic models of Nu Eridani and 12 Lacertae considering opacity uncertainties, and investigates mode excitation and internal rotation profiles.

Findings

Significant difference in results using OP and OPAL opacity data.

Evidence of increased rotation rate from envelope to core.

Models show instability of low-frequency g-modes in Nu Eri with OP data.

Abstract

The rich oscillation spectra determined for the two stars, Nu Eridani and 12 Lacertae, present an interesting challenge to stellar modelling. The stars are hybrid objects showing a number of modes at frequencies typical for Beta Cep stars but also one mode at frequency typical for SPB stars. We construct seismic models of these stars considering uncertainties in opacity and element distribution. We also present estimate of the interior rotation rate and address the matter of mode excitation. We use both the OP and OPAL opacity data and find significant difference in the results. Uncertainty in these data remains a major obstacle in precise modelling of the objects and, in particular, in estimating the overshooting distance. We find evidence for significant rotation rate increase between envelope and core in the two stars. Instability of low-frequency g-modes was found in seismic models of Nu Eri built with the OP data, but at frequencies higher than those measured in the star. No such instability was found in models of 12 Lac. We do not have yet a satisfactory explanation for low frequency modes. Some enhancement of opacity in the driving zone is required but we argue that it cannot be achieved by the iron accumulation, as it has been proposed.