BRITE-Constellation high-precision time-dependent photometry of the early-O-type supergiant Zeta Puppis unveils the photospheric drivers of its small- and large-scale wind structures


Tahina Ramiaramanantsoa (1,2), Anthony F. J. Moffat (1,2), Robert Harmon (3), Richard Ignace (4), Nicole St-Louis (1,2), Dany Vanbeveren (5), Tomer Shenar (6), Herbert Pablo (1,2), Noel D. Richardson (7), Ian D. Howarth (8), Ian R. Stevens (9), Caroline Piaulet (1), Lucas St-Jean (1), Thomas Eversberg (10), Andrzej Pigulski (11), Adam Popowicz (12), Rainer Kuschnig (13), Elzbieta Zoclonska (14), Bram Buysschaert (15,16), Gerald Handler (14), Werner W. Weiss (13), Gregg A. Wade (17), Slavek M. Rucinski (18), Konstanze Zwintz (19), Paul Luckas (20), Bernard Heathcote (21), Paulo Cacella (22), Jonathan Powles (23), Malcolm Locke (24), Terry Bohlsen (25), André-Nicolas Chené (26), Brent Miszalski (27,28), Wayne L. Waldron (29), Marissa M. Kotze (27,28), Enrico J. Kotze (27) and Torsten Böhm (30,31)

(1) Université de Montréal, Canada
(2) Centre de Recherche en Astrophysique du Québec, Canada
(3) Ohio Wesleyan University, USA
(4) East Tennessee State University, USA
(5) Vrije Universiteit Brussel, Belgium
(6) Universität Potsdam, Germany
(7) University of Toledo, USA
(8) University College London, UK
(9) University of Birmingham, UK
(10) Schnörringen Telescope Science Institute, Germany
(11) Uniwersytet Wroclawski, Poland
(12) Instytut Automatyki, Politechnika Slaska, Poland
(13) Universität Wien, Austria
(14) Nicolaus Copernicus Astronomical Center, Poland
(15) LESIA, Observatoire de Paris, France
(16) KU Leuven, Belgium
(17) Royal Military College of Canada, Canada
(18) University of Toronto, Canada
(19) Universität Innsbruck, Austria
(20) International Centre for Radio Astronomy Research, The University of Western Australia, Australia
(21) SASER Team, Domain Observatory, Australia
(22) SASER Team, Dogsheaven Observatory, Brazil
(23) SASER Team, Latham Observatory, Australia
(24) SASER Team, R. F. Joyce Observatory, New Zealand
(25) SASER Team, Mirranook Observatory, Australia
(26) Gemini Observatory, Northern Operations Center, USA
(27) South African Astronomical Observatory, South Africa
(28) South African Large Telescope, South Africa
(29) Eureka Scientific Inc., USA
(30) Université de Toulouse, France
(31) Centre National de la Recherche Scientifique, Institut de Recherche en Astrophysique et Planétologie, France

From 5.5 months of dual-band optical photometric monitoring at the 1 mmag level, BRITE-Constellation has revealed two simultaneous types of variability in the O4I(n)fp star Zeta Puppis: one single periodic non-sinusoidal component superimposed on a stochastic component. The monoperiodic component is the 1.78 d signal previously detected by Coriolis/SMEI, but this time along with a prominent first harmonic. The shape of this signal changes over time, a behaviour that is incompatible with stellar oscillations but consistent with rotational modulation arising from evolving bright surface inhomogeneities. By means of a constrained non-linear light curve inversion algorithm we mapped the locations of the bright surface spots and traced their evolution. Our simultaneous ground-based multi-site spectroscopic monitoring of the star unveiled cyclical modulation of its He II 4686 wind emission line with the 1.78-day rotation period, showing signatures of Corotating Interaction Regions (CIRs) that turn out to be driven by the bright photospheric spots observed by BRITE. Traces of wind clumps are also observed in the He II 4686 line and are correlated with the amplitudes of the stochastic component of the light variations probed by BRITE at the photosphere, suggesting that the BRITE observations additionally unveiled the photospheric drivers of wind clumps in Zeta Pup and that the clumping phenomenon starts at the very base of the wind. The origins of both the bright surface inhomogeneities and the stochastic light variations remain unknown, but a subsurface convective zone might play an important role in the generation of these two types of photospheric variability.

Reference: To appear in MNRAS
Status: Manuscript has been accepted

Weblink: https://arxiv.org/abs/1710.08414

Comments: 44 pages, 28 figures, 6 Tables

Email: tahina@astro.umontreal.ca