Time-series photometry of the O4 I(n)fp star zeta Puppis
Ian D. Howarth (1)
Ian R. Stevens (2)
(1) Department of Physics and Astronomy, University College London, Gower St., London WC1E 6BT, UK
(2) School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
We report a time-series analysis of the O4I(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.
Reference: Accepted in MNRAS
Status: Manuscript has been accepted