An asteroseismic study of the beta Cephei star theta Ophiuchi: constraints on global stellar parameters and core overshooting

TL;DR

This seismic study of theta Ophiuchi uses observed pulsation modes and spectroscopy to constrain stellar parameters, revealing core overshooting and rotation effects in a beta Cephei star.

Contribution

The paper provides the first detailed seismic analysis of theta Ophiuchi, constraining its mass, core overshooting, and rotation using multiple pulsation modes and spectroscopic data.

Findings

Constrained stellar mass to 8.2 +/- 0.3 solar masses.

Detected core overshooting with alpha_ov = 0.44 +/- 0.07.

Reproduced non-equidistance of the triplet with second order rotational effects.

Abstract

We present a seismic study of the beta Cephei star theta Ophiuchi. Our analysis is based on the observation of one radial mode, one rotationally split l = 1 triplet and three components of a rotationally split l = 2 quintuplet for which the m-values were well identified by spectroscopy. We identify the radial mode as fundamental, the triplet as p_1 and the quintuplet as g_1. Our NLTE abundance analysis results in a metallicity and CNO abundances in full agreement with the most recent updated solar values. With X \in [0.71,0.7211] and Z \in [0.009,0.015], and using the Asplund et al. (2005) mixture but with a Ne abundance about 0.3 dex larger (Cunha et al. 2006), the matching of the three independent modes, enables us to deduce constrained ranges for the mass (M = 8.2 +/- 0.3 Msun) and central hydrogen abundance (X_c = 0.38 +/- 0.02) of theta Oph and to prove the occurrence of core overshooting (alpha_ov = 0.44 +/- 0.07). We also derive an equatorial rotation velocity of 29 +/- 7 km/s. Moreover, we show that the observed non-equidistance of the l=1 triplet can be reproduced by second order effects of rotation. Finally, we show that the observed rotational splitting of two modes cannot rule out a rigid rotation model.