MOST detects corotating bright spots on the mid-O type giant ξ Persei

Abstract

We have used the MOST (Microvariability and Oscillations of STars) microsatellite to obtain four weeks of contiguous high-precision broadband visual photometry of the O7.5III(n)((f)) star ξ Persei in November 2011. This star is well known from previous work to show prominent DACs (Discrete Absorption Components) on time-scales of about 2 d from UV spectroscopy and NRP (Non Radial Pulsation) with one (l = 3) p-mode oscillation with a period of 3.5 h from optical spectroscopy. Our MOST-orbit (101.4 min) binned photometry fails to reveal any periodic light variations above the 0.1 mmag 3-sigma noise level for periods of hours, while several prominent Fourier peaks emerge at the 1 mmag level in the two-day period range. These longer-period variations are unlikely due to pulsations, including gravity modes. From our simulations based upon a simple spot model, we deduce that we are seeing the photometric modulation of several co-rotating bright spots on the stellar surface. In our model, the starting times (random) and lifetimes (up to several rotations) vary from one spot to another yet all spots rotate at the same period of 4.18 d, the best-estimated rotation period of the star. This is the first convincing reported case of co-rotating bright spots on an O star, with important implications for drivers of the DACs (resulting from CIRs - Corotating Interaction Regions) with possible bright-spot generation via a breakout at the surface of a global magnetic field generated by a subsurface convection zone.

arXiv comment9 pages, 4 figures, 2 tables, MNRAS in press

References in corpus (25)

• The CoRoT satellite in flight : description and performance
• Sub-surface convection zones in hot massive stars and their observable consequences
• Hydrodynamical Simulations of Corotating Interaction Regions and Discrete Absorption Components in Rotating O-Star Winds
• Bright OB stars in the Galaxy - III. Constraints on the radial stratification of the clumping factor in hot star winds from a combined Halpha, IR and radio analysis
• Dynamical Simulations of Magnetically Channeled Line-Driven Stellar Winds: II. The Effects of Field-Aligned Rotation
• Stellar Diameters and Temperatures III. Main Sequence A, F, G, & K Stars: Additional high-precision measurements and empirical relations
• Catalog of Galactic Beta Cephei Stars
• Making Sense of Sunspot Decay I: Parabolic Decay Law and Gnevyshev-Waldmeier Relation
• Magnetic spots on hot massive stars
• Self-consistent 2D models of fast rotating early-type star
• Variability in the CoRoT photometry of three hot O-type stars. HD 46223, HD 46150 and HD 46966
• An asteroseismic study of the O9V star HD 46202 from CoRoT space-based photometry
• Detection of frequency spacings in the young O-type binary HD 46149 from CoRoT photometry
• Beta Cephei stars in the ASAS-3 data. II. 103 new Beta Cephei stars and a discussion of low-frequency modes
• Increasing Lifetime of Recurrent Sunspot Groups within the Greenwich Photoheliographic Results
• Plaskett's Star: Analysis of the CoRoT photometric data
• Reduction of time-resolved space-based CCD photometry developed for MOST Fabry Imaging data
• Spectroscopic and photometric variability of the O9.5Vp star HD93521
• WR 110: A Single Wolf-Rayet Star With Corotating Interaction Regions In Its Wind?
• Detectability of small-scale magnetic fields in early-type stars
• Low-amplitude rotational modulation rather than pulsations in the CoRoT B-type supergiant HD 46769
• Spectral Energy Distributions of Be and Other Massive Stars
• Amplitude variability in satellite photometry of the non-radially pulsating O9.5V star zeta Oph
• "Stellar Prominences" on OB stars to explain wind-line variability
• Epoch-dependent absorption line profile variability in lambda Cep

Cited by in corpus (37)

• Short-term variability and mass loss in Be stars I. BRITE satellite photometry of $\eta$ and $\mu$ Centauri
• Envelope Convection, Surface Magnetism and Spots in A- and late B-type Stars
• 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
• Rotational modulation in TESS B stars
• On the Origin of Stochastic, Low-Frequency Photometric Variability in Massive Stars
• Kepler's first view of O-star variability: K2 data of five O stars in Campaign 0 as a proof-of-concept for O-star asteroseismology
• B fields in OB stars (BOB): on the detection of weak magnetic fields in the two early B-type stars beta CMa and epsilon CMa
• TESS observations of Be stars: a new interpretation
• The X-ray catalog of spectroscopically identified Galactic O stars: Investigating the dependence of X-ray luminosity on stellar and wind parameters
• The X-ray emission of Be+stripped star binaries
• Investigating the origin of cyclical wind variability in hot, massive stars - II. Hydrodynamical simulations of co-rotating interaction regions using realistic spot parameters for the O giant $\xi$ Persei
• A Coordinated X-ray and Optical Campaign of the Nearest Massive Eclipsing Binary, delta Orionis Aa: III. Analysis of Optical Photometric MOST and Spectroscopic (Ground Based) Variations
• Searching for a magnetic field in Wolf-Rayet stars using FORS2 spectropolarimetry
• The IACOB project VIII. Searching for empirical signatures of binarity in fast-rotating O-type stars
• Studying the photometric and spectroscopic variability of the magnetic hot supergiant $\zeta$ Orionis Aa
• Limb-darkening coefficients from line-blanketed non-LTE hot-star model atmospheres
• On the Origin of Wind Line Variability in O Stars
• An extensive spectroscopic time-series of three Wolf-Rayet stars. I. The lifetime of large-scale structures in the wind of WR 134
• X-ray diagnostics of massive star winds
• The distance, rotation, and physical parameters of zeta Pup
• Multiple short-lived stellar prominences on O stars: The O6.5I(n)fp star lambda Cephei
• BRITE-Constellation reveals evidence for pulsations in the enigmatic binary $\eta$ Carinae
• The search for magnetic fields in two Wolf-Rayet stars and the discovery of a variable magnetic field in WR55
• Variations on a theme -- the puzzling behaviour of Schulte 12
• Coordinated UV and X-ray spectroscopic observations of the O-type giant xi Per: the connection between X-rays and large-scale wind structure
• Magnetic Archaeology of Early-Type Stellar Dynamos
• Ultraviolet Spectropolarimetric Diagnostics of Hot Star Magnetospheres
• Magnetic fields in O-, B- and A-type stars on the main sequence
• A detailed X-ray investigation of zeta Puppis IV. Further characterization of the variability
• Ultraviolet Spectropolarimetry with Polstar: Clumping and Mass-loss Rate Corrections
• Onboard Dynamic Image Exposure Control for the Star-Planet Activity Research CubeSat (SPARCS)
• The magnetic, spectroscopic, and photometric variability of the Wolf-Rayet star WR55
• Sub-photospheric fluctuations in magnetized radiative envelopes: contribution from unstable magnetosonic waves
• Is λ Cep a pulsating star?
• X-ray diagnostics of massive star winds
• A magnetic field detection in the massive O-type bright giant 63 Oph
• Beam me up, Spotty: Toward a new understanding of the physics of massive star photospheres