Asteroseismology of the β Cephei star 12 (DD) Lacertae: photometric observations, pulsational frequency analysis and mode identification

Abstract

We report a multisite photometric campaign for the β Cephei star 12 Lacertae. 750 h of high‐quality differential photoelectric Strömgren, Johnson and Geneva time‐series photometry were obtained with nine telescopes during 190 nights. Our frequency analysis results in the detection of 23 sinusoidal signals in the light curves. Ten of those correspond to independent pulsation modes, and the remainder are combination frequencies. We find some slow aperiodic variability such as that seemingly present in several β Cephei stars. We perform mode identification from our colour photometry, derive the spherical degree ℓ for the five strongest modes unambiguously and provide constraints on ℓ for the weaker modes. We find a mixture of modes of 0 ≤ℓ≤ 4. In particular, we prove that the previously suspected rotationally split triplet within the modes of 12 Lac consists of modes of different ℓ; their equal frequency splitting must thus be accidental. One of the periodic signals we detected in the light curves is argued to be a linearly stable mode excited to visible amplitude by non‐linear mode coupling via a 2:1 resonance. We also find a low‐frequency signal in the light variations whose physical nature is unclear; it could be a parent or daughter mode resonantly coupled. The remaining combination frequencies are consistent with simple light‐curve distortions. The range of excited pulsation frequencies of 12 Lac may be sufficiently large that it cannot be reproduced by standard models. We suspect that the star has a larger metal abundance in the pulsational driving zone, a hypothesis also capable of explaining the presence of β Cephei stars in the Large Magellanic Cloud.

An asteroseismic study of the O9V star HD 46202 from CoRoT space-based photometry

“…For this latter target, Dziembowski & Jerzykiewicz (1999) assumed that three of the strongest modes, almost equidistant, belong to the same multiplet in their seismic modelling. Later, a photometric mode identification by Handler et al (2006) ruled out this assumption by proving that the three modes are actually associated with three different values of the degree . It is obvious that reliable empirical mode identification from multicolour photometry, and/or spectroscopy, is indispensable for definite conclusions.…”

CoRoT's view of newly discovered B-star pulsators: results for 358 candidate B pulsators from the initial run's exoplanet field data

“…This might come from nonlinear effects, e.g., nonlinear coupling between modes (Buchler et al 1997;Handler et al 2006;Degroote et al 2009, e.g.). In model (6), the linear parameters still have to be fitted, but are sometimes expected to be in phase or in antiphase with each other.…”

Interpretation of the BRITE oscillation data of the hybrid pulsator ν Eridani: a call for the modification of stellar opacities

“…Despite various improvements in the calculation of stellar opacities, there are many indications that something is still missing in these data and/or has not been correctly included. One example is the B-type main sequence pulsators, which exhibit both pressure and high-order gravity modes, e.g., ν Eridani , 12 Lacertae (Handler et al 2006), γ Pegasi (Handler et al 2009). There are also bags of such pulsators identified from the space data from Kepler and CoRoT missions (e.g., Degroote et al 2009, Balona et al 2011, 2015a.…”