Time-series photometry of the O4 I(n)fp star zeta Puppis

TL;DR

This study analyzes optical photometry of zeta Puppis, revealing a dominant 1.78-day periodic signal likely due to stellar pulsation, and finds no evidence supporting previously suggested rotation periods or magnetic modulation.

Contribution

First detailed time-series photometry of zeta Puppis revealing a specific pulsation period and challenging previous rotation-based interpretations.

Findings

Detected a 1.78-day periodic signal with ~7 mmag amplitude.

No evidence of the proposed 5.1-day rotation period.

Signal amplitude varies over timescales of 10-100 days.

Abstract

We report a time-series analysis of the O4 I(n)fp star zeta Pup, based on optical photometry obtained with the SMEI instrument on the Coriolis satellite, 2003--2006. A single astrophysical signal is found, with P = (1.780938 \pm 0.000093) d and a mean semi-amplitude of (6.9 \pm 0.3) mmag. There is no evidence for persistent coherent signals with semi-amplitudes in excess of ca. 2~mmag on any of the timescales previously reported in the literature. In particular, there is no evidence for a signature of the proposed rotation period, ca. 5.1~days; zeta Pup is therefore probably not an oblique magnetic rotator. The 1.8-day signal varies in amplitude by a factor ca. 2 on timescales of 10--100d (and probably by more on longer timescales), and exhibits modest excursions in phase, but there is no evidence for systematic changes in period over the 1000-d span of our observations. Rotational modulation and stellar-wind variability appear to be unlikely candidates for the underlying mechanism; we suggest that the physical origin of the signal may be pulsation associated with low-l oscillatory convection modes.