Is \lambda\ Cep a pulsating star?

TL;DR

This study investigates the variability of mbda Cephei, analyzing spectral data to determine if its fluctuations are due to non-radial pulsations or transient phenomena, finding evidence inconsistent with stable pulsations.

Contribution

The paper provides new spectral observations and analysis that challenge the non-radial pulsation hypothesis for mbda Cephei, suggesting transient magnetic activity as a possible cause.

Findings

Spectral variations sometimes show redward movement in absorption lines.

Periods of variability are inconsistent across datasets.

Variability appears short-lived, lasting a few days.

Abstract

It has been proposed that the variability seen in absorption lines of the O6Ief star \lambda\ Cep is periodical and due to non-radial pulsations (NRP). We have obtained new spectra during six campaigns lasting between five and nine nights. In some datasets we find recurrent spectral variations which move redward in the absorption line profile, consistent with perturbations on the stellar surface of a rotating star. However the periods found are not stable between datasets, at odds with the NRP hypothesis. Moreover, even when no redward trend is found in a full dataset of an observing campaign, it can be present in a subset, suggesting that the phenomenon is short-lived, of the order of a few days, and possibly linked to transient magnetic loops.