Plaskett's Star: Analysis of the CoRoT photometric data

TL;DR

This study analyzes high-quality CoRoT photometric data of Plaskett's Star to detect variability, pulsations, and orbital effects, providing new insights into its binary system and potential seismic activity.

Contribution

It presents the first detailed frequency analysis of Plaskett's Star using space-based photometry, identifying orbital and pulsation-related variations and revealing a hot spot on the primary star.

Findings

Detected about 43 significant frequency peaks, including orbital and pulsation harmonics.

Identified a hot spot on the primary star facing the secondary.

Provided initial data for future seismic modeling of the system.

Abstract

The SRa02 of the CoRoT space mission for Asteroseismology was partly devoted to stars belonging to the Mon OB2 association. An intense monitoring was performed on Plaskett's Star (HD47129) and the unprecedented quality of the light curve allows us to shed new light on this very massive, non-eclipsing binary system. We particularly aimed at detecting periodic variability which might be associated with pulsations or interactions between both components. We also searched for variations related to the orbital cycle which could help to constrain the inclination and the morphology of the binary system. A Fourier-based prewhitening and a multiperiodic fitting procedure were applied to analyse the time series and extract the frequencies of variations. We describe the noise properties to tentatively define an appropriate significance criterion, to only point out the peaks at a certain significance level. We also detect the variations related to the orbital motion and study them by using the NIGHTFALL program. The periodogram exhibits a majority of peaks at low frequencies. Among these peaks, we highlight a list of about 43 values, including notably two different sets of harmonic frequencies whose fundamental peaks are located at about 0.07 and 0.82d-1. The former represents the orbital frequency of the binary system whilst the latter could probably be associated with non-radial pulsations. The study of the 0.07d-1 variations reveals the presence of a hot spot most probably situated on the primary star and facing the secondary. The investigation of this unique dataset constitutes a further step in the understanding of Plaskett's Star. These results provide a first basis for future seismic modelling. The existence of a hot region between both components renders the determination of the inclination ambiguous.