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Title: The Effects of Magnetic Fields on the Dynamics of Radiation Pressure–dominated Massive Star Envelopes

Journal Article · · The Astrophysical Journal (Online)
ORCiD logo [1]; ORCiD logo [2];  [3]; ORCiD logo [4];  [5]
  1. Univ. of California, Santa Barbara, CA (United States). Kavli Inst. for Theoretical Physics
  2. Univ. of California, Santa Barbara, CA (United States). Kavli Inst. for Theoretical Physics; Flatiron Inst., New York, NY (United States). Center for Computational Astrophysics
  3. Univ. of California, Santa Barbara, CA (United States). Kavli Inst. for Theoretical Physics; Univ. of California, Santa Barbara, CA (United States). Dept. of Physics
  4. Univ. of California, Berkeley, CA (United States). Astronomy Dept. and Theoretical Astrophysics Center
  5. Univ. of California, Santa Barbara, CA (United States). Dept. of Physics
+ Show Author Affiliations

We use three-dimensional radiation magnetohydrodynamic simulations to study the effects of magnetic fields on the energy transport and structure of radiation pressure–dominated main sequence massive star envelopes at the region of the iron opacity peak. We focus on the regime where the local thermal timescale is shorter than the dynamical timescale, corresponding to inefficient convective energy transport. We begin with initially weak magnetic fields relative to the thermal pressure, from 100 to 1000 G in differing geometries. The unstable density inversion amplifies the magnetic field, increasing the magnetic energy density to values close to equipartition with the turbulent kinetic energy density. By providing pressure support, the magnetic field's presence significantly increases the density fluctuations in the turbulent envelope, thereby enhancing the radiative energy transport by allowing photons to diffuse out through low-density regions. Magnetic buoyancy brings small-scale magnetic fields to the photosphere and increases the vertical energy transport, with the energy advection velocity proportional to the Alfvén velocity, although in all cases we study, photon diffusion still dominates the energy transport. The increased radiative and advective energy transport causes the stellar envelope to shrink by several scale heights. We also find larger turbulent velocity fluctuations compared with the purely hydrodynamic case, reaching $$\approx 100\,{{\rm{km}}{\rm{s}}}^{-1}$$ at the stellar photosphere. The photosphere also shows vertical oscillations with similar averaged velocities and periods of a few hours. The increased turbulent velocity and oscillations will have strong impacts on the line broadening and periodic signals in massive stars.

Research Organization:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
Sponsoring Organization:
USDOE Office of Science (SC)
Grant/Contract Number:
AC02-05CH11231
OSTI ID:
1524229
Journal Information:
The Astrophysical Journal (Online), Vol. 843, Issue 1; ISSN 1538-4357
Publisher:
Institute of Physics (IOP)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 12 works
Citation information provided by
Web of Science

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Cited By (4)

A Complete Census of Luminous Stellar Variability on Day to Decade Timescales journal September 2018
The Long-term Evolution and Appearance of Type Iax Postgenitor Stars journal February 2019
Super-Eddington Accretion Disks around Supermassive Black Holes journal July 2019
A Complete Census of Luminous Stellar Variability on Day to Decade Timescales text January 2018

Figures / Tables (14)

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79 ASTRONOMY AND ASTROPHYSICS
magnetohydrodynamics (MHD)
methods: numerical
radiative transfer
stars: massive