Numerical Simulations of a Rotating Red Giant Star. I. Three-Dimensional Models of Turbulent Convection and Associated Mean Flows

Brun, Allan Sacha; Palacios, Ana

doi:10.1088/0004-637x/702/2/1078

Cited by 91 publications

(109 citation statements)

References 68 publications

(107 reference statements)

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“…This situation should change once a saturation of the dynamo is reached. As also found in Brun & Palacios (2009) for a more evolved red giant, the enthalpy flux dominates the energy transport. When converted to luminosity it reaches 160% of the total stellar luminosity.…”

Section: Dynamo Onset Internal Transport and Magnetic Propertiessupporting

confidence: 73%

On dynamo action in the giant star Pollux: first results

Brun¹

2013

Proc. IAU

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Abstract. We present preliminary results of a 3D MHD simulation of the convective envelope of the giant star Pollux for which the rotation period and the magnetic field intensity have been measured from spectroscopic and spectropolarimetric observations. This giant is one of the first single giants with a detected magnetic field, and the one with the weakest field so far. Our aim is to understand the development and the action of the dynamo in its extended convective envelope. Context and numerical setupThe detection of magnetic fields in the atmosphere of red giant stars using spectropolarimetry (see Aurière and Konstantinova-Antova in this volume) brings the opportunity to get an insight on the secular evolution of magnetic fields in solar-type and intermediate-mass stars. Spectropolarimetry allows to estimate the magnetic fields intensity, the doppler imaging of magnetic red giants being a delicate matter in part due to the usually long rotation period that characterizes these objects. The star Pollux is one of the first giants with a detected magnetic field, and its intensity of about 1 G, is the weakest detected so far. Here, we present preliminary results of a fully 3-D dynamo computation carried out with the Anelastic Spherical Harmonic (ASH) version 2.0 code (Featherstone et al. 2013, Brun et al. 2004, for the entire convective envelope (75% of the total radius, strong stratification) of a 2.5 M with R = 9 R and L = 40 L , well representative of the star Pollux (see Aurière et al. 2009). The hydrodynamical progenitor was computed with Ω = 2.63 10 −7 rad.s −1 , corresponding to a υ sini ≈ 1.3 km.s −1 , in good agreement with published values. Using a magnetic Prandtl number of the simulation of P m = 3, we have next initialized the magnetic field with a multipole l = 3, m = 2 seed field, with an initial total magnetic energy ME less than 10 −3 of the total kinetic energy. Dynamo onset, internal transport and magnetic propertiesOur simulation is still running and as of today the dynamo is in the linear regime with an exponential growth of ME having to enter yet the saturated regime. At this point of the simulation, the total magnetic energy only corresponds to 0.1% of the total kinetic energy. The ME is dominated by non-axisymmetric contributions of the toroidal and poloidal fields. The purely axisymmetric components TME and PME are growing but very weak. The radial energy flux balance has reached an equilibrium. The radial energy transport by the Poynting flux is negligible (at a level of 10 −5 ) at this stage of the simulation. This situation should change once a saturation of the dynamo is reached. 363at https://www.cambridge.org/core/terms. https://doi

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Section: Dynamo Onset Internal Transport and Magnetic Propertiessupporting

confidence: 73%

On dynamo action in the giant star Pollux: first results

Brun¹

2013

Proc. IAU

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“…The fact of using a constant α for the mixing length parameter, based on a solar calibration, is obviously not appropriate anymore. Hydrodynamical simulations of the envelope of giant stars (Freytag et al 2002;Woodward et al 2003;Brun & Palacios 2009) have clearly established that many of the assumptions on which the MLT is based are violated, thus casting doubt on the reliability of this formalism in giant stars. Suspicions are also raised when trying to determine the location of the convective boundaries when active nuclear burning is operating at the base of the envelope.…”

Section: Discussion and Summarymentioning

confidence: 99%

Evolution of massive AGB stars

Siess

2010

A&A

186

323

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Aims. We present the first simulations of the full evolution of super-AGB stars through the entire thermally pulsing AGB phase. We analyse their structural and evolutionary properties and determine the first SAGB yields.Methods. Stellar models of various initial masses and metallicities were computed using standard physical assumptions which prevents the third dredge-up from occurring. A postprocessing nucleosynthesis code was used to compute the SAGB yields, to quantify the effect of the third dredge-up (3DUP), and to assess the uncertainties associated with the treatment of convection.Results. Owing to their massive oxygen-neon core, SAGB stars suffer weak thermal pulses, have very short interpulse periods and develop very high temperatures at the base of their convective envelope (up to 140 × 10 8 K), leading to very efficient hot bottom burning. SAGB stars are consequently heavy manufacturers of 4 He, 13 C, and 14 N. They are also able to inject significant amounts of 7 Li, 17 O, 25 Mg, and 26,27 Al in the interstellar medium. The 3DUP mainly affects the CNO yields, especially in the lower metallicity models. Our post-processing simulations also indicate that changes in the temperature at the base of the convective envelope, which would result from a change in the efficiency of convective energy transport, have a dramatic impact on the yields and represent another major source of uncertainty.

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“…This code has been extensively tested and used for computing several aspects of the solar interior (e.g., Browning et al 2006;Brun & Toomre 2002;Brun et al 2004;DeRosa et al 2002;Miesch et al 2006), rapidly rotating young stars (Ballot et al 2007;Brown 2009;Brown et al 2008Brown et al , 2011, the convective cores of massive stars (Browning et al 2004a,b;Featherstone et al 2009), fully convective low mass stars (Browning 2008), red giant stars (Brun & Palacios 2009), and pre-main-sequence stars (Bessolaz & Brun, in this volume;Bessolaz & Brun 2011). We briefly describe the basic aspects of the code here, but the reader can find further details of the code in those previous works (see especially, Brun et al 2004;Clune et al 1999).…”

Section: Simulation Methodsmentioning

confidence: 99%

Convection and differential rotation properties of G and K stars computed with the ASH code

Matt

Cao

Brown³

et al. 2011

Astron Nachr

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The stellar luminosity and depth of the convective envelope vary rapidly with mass for G-and K-type main sequence stars. In order to understand how these properties influence the convective turbulence, differential rotation, and meridional circulation, we have carried out 3D dynamical simulations of the interiors of rotating main sequence stars, using the anelastic spherical harmonic (ASH) code. The stars in our simulations have masses of 0.5, 0.7, 0.9, and 1.1 M , corresponding to spectral types K7 through G0, and rotate at the same angular speed as the Sun. We identify several trends of convection zone properties with stellar mass, exhibited by the simulations. The convective velocities, temperature contrast between up-and downflows, and meridional circulation velocities all increase with stellar luminosity. As a consequence of the trend in convective velocity, the Rossby number (at a fixed rotation rate) increases and the convective turnover timescales decrease significantly with increasing stellar mass. The three lowest mass cases exhibit solar-like differential rotation, in a sense that they show a maximum rotation at the equator and minimum at higher latitudes, but the 1.1 M case exhibits anti-solar rotation. At low mass, the meridional circulation is multi-cellular and aligned with the rotation axis; as the mass increases, the circulation pattern tends toward a unicellular structure covering each hemisphere in the convection zone.

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Numerical Simulations of a Rotating Red Giant Star. I. Three-Dimensional Models of Turbulent Convection and Associated Mean Flows

Cited by 91 publications

References 68 publications

On dynamo action in the giant star Pollux: first results

On dynamo action in the giant star Pollux: first results

Evolution of massive AGB stars

Convection and differential rotation properties of G and K stars computed with the ASH code

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