Asteroseismology of the   Cephei star   Eridani - I. Photometric observations and pulsational frequency analysis

Abstract

We undertook a multisite photometric campaign for the β Cephei star ν Eridani. More than 600 h of differential photoelectric uvyV photometry were obtained with 11 telescopes during 148 clear nights.The frequency analysis of our measurements shows that the variability of ν Eri can be decomposed into 23 sinusoidal components, eight of which correspond to independent pulsation frequencies between 5 and 8 cd −1 . Some of these are arranged in multiplets, which suggests rotational m-mode splitting of non-radial pulsation modes as the cause. If so, the rotation period of the star must be between 30 and 60 d.One of the signals in the light curves of ν Eri has a very low frequency of 0.432 cd −1 . It can be a high-order combination frequency or, more likely, an independent pulsation mode. In the latter case, ν Eri would be both a β Cephei star and a slowly pulsating B (SPB) star.The photometric amplitudes of the individual pulsation modes of ν Eri appear to have increased by about 20 per cent over the last 40 years. So have the amplitudes of the dominant combination frequencies of the star. Among the latter, we could only identify sum frequencies with certainty, not difference frequencies, which suggests that neither light-curve distortion in its simplest form nor resonant mode coupling is their single cause.One of our comparison stars, µ Eridani, turned out to be variable with a dominant time-scale of 1.62 d. We believe either that it is an SPB star just leaving its instability strip or that its variations are of rotational origin.

Evidence for nonlinear resonant mode coupling in the $\mathsf{\beta}$ Cephei star HD 180642 (V1449 Aquilae) from CoRoT photometry

“…in ν Eri (Handler et al 2004) and in 12 Lac (Handler et al 2006). For these stars, only positive combinations were detected.…”

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

“…There is a small overlap between their instability regions, where hybrid pulsators of spectral type near B3, exhibiting both high-order g and loworder p modes, are predicted but not yet observed. On the other hand, these two types of modes have been observed in hotter β Cep stars (ν Eri: Handler et al 2004;12 Lac: Handler et al 2006; γ Peg: Chapellier et al 2006). The mechanism that drives the pulsations is the κ mechanism (Dziembowski & Pamiatnykh 1993) because of the Fe-group opacity bump at T ∼ 2 × 10 5 K, which means that the excitation of modes in those stars is sensitive to the behaviour of opacity in the stellar interior and to the abundance of Fe-group elements.…”

The CoRoT B-type binary HD 50230: a prototypical hybrid pulsator with g-mode period and p-mode frequency spacings

“…This concerns the stars ν Eri (Handler et al 2004;De Ridder et al 2004), 12 Lac (Handler et al 2006;Desmet et al 2009) and γ Peg (Handler et al 2009). In all these examples, however, the pressure modes are dominant over the gravity modes.…”