Sub-surface convection zones in hot massive stars and their observable consequences

By Matteo Cantiello, N. Langer, I. Brott, A. D. Koter, S. Shore, J. Vink, A. Voegler, D. Lennon, S.-C. Yoon. 2009

258 citations recorded by the source corpus.

Context. We study the convection zones in the outer envelope of hot massive stars which are caused by opacity peaks associated with iron and helium ionization. Aims. We determine the occurrence and properties of these convection zones as function of the stellar parameters. We then confront our results with observations of OB stars. Methods. A stellar evolution code is used to compute a grid of massive star models at different metallicities. In these models, the mixing length theory is used to characterize the envelope convection zones. Results. We find the iron convection zone (FeCZ) to be more prominent fo r lower surface gravity, higher luminosity and higher initi al metallicity. It is absent for luminosities below about 10 3.2 L⊙, 10 3.9 L⊙, and 10 4.2 L⊙ for the Galaxy, LMC and SMC, respectively. We map the strength of the FeCZ on the Hertzsprung-Russell diagram for three metallicities, and compare this with the occurrence of observational phenomena in O stars: microturbulence, non-radial pulsations, wind clumping, and line profile variabil ity. Conclusions. The confirmation of all three trends for the FeCZ as function o f stellar parameters by empirical microturbulent velociti es argues for a physical connection between sub-photospheric convective motions and small scale stochastic velocities i n the photosphere of O- and B-type stars. We further suggest that clumping in the inner parts of the winds of OB stars could be caused by the same mechanism, and that magnetic fields produced in the FeCZ coul d appear at the surface of OB stars as diagnosed by discrete absorption components in ultraviolet absorption lines.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/9388030736e9ba98e88cd06942b0e9bba93b25ce

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Citations in the corpus

Rotating massive main-sequence stars: II. Simulating a population of LMC early B-type stars as a test of rotational mixing (2011, background): “…et al. 2007; Puls et al. 2008), intermittent discrete absorption components in UV absorption lines (Prinja & Howarth 1988; Kaper et al. 1997), micro- and macro-turbulence (Cantiello et al. 2009; Aerts et al. 2009), and non-thermal X-ray emission (Babel & Montmerle 1997; ud-Doula & Owocki 2002).”
Mass Loss: Its Effect on the Evolution and Fate of High-Mass Stars (2014, background): “…for this study and if they may overestimate the reductions in Ṁ that are applied, this nevertheless forced an important discussion in massive star research by highlighting the potential influence of clumping. because of sub-surface convection driven by the Fe opacity bump (Cantiello et al. 2009).”
The IACOB project - I. Rotational velocities in northern Galactic O- and early B-type stars revisited. The impact of other sources of line-broadening (2013, background): “…from an observational point of view, can we increase our knowledge about the microturbulence in Otype stars?, and (c) from a theoretical/modeling point of view, explore further the scenario proposed by Cantiello et al. (2009) and compare the corresponding predictions with observation l constraints.”
Present-day cosmic abundances - A comprehensive study of nearby early B-type stars and implications for stellar and Galactic evolution and interstellar dust models (2012, unknown): “Only recently, a physical explanation for the phenomenon ofmicroturbulence in hot stars was suggested, likely being a consequence of subsurface convection (Cantiello et al. 2009), similar to the case of solar-type stars.”
MODULES FOR EXPERIMENTS IN STELLAR ASTROPHYSICS (MESA): PLANETS, OSCILLATIONS, ROTATION, AND MASSIVE STARS (2013, background): “Note that dynamo action in a subsurface convective layer is in principle possible also in early-type stars (Cantiello et al. 2009; Cantiello & Braithwaite 2011).”
Wind modelling of very massive stars up to 300 solar masses (2011, background): “The potential e ﬀ ects may involve strange-mode pulsations (e.g. Glatzel & Kiriakidis 1993), subsurface convection (Cantiello et al. 2009), or an inﬂation of the outer stellar envelope (e.g. Ishii et al. 1999).”
Merging binary black holes formed through chemically homogeneous evolution in short-period stellar binaries (2015, background): “The envelope is stable against convection, apart from very small regions near the surface (Maeder 1980; Cantiello et al. 2009).”