Rotational mixing in low-mass stars: II. Self-consistent models of Pop II RGB stars

By A. Palacios, C. Charbonnel, Suzanne Talon, L. Siess. 2006

152 citations recorded by the source corpus.

Aims. In this paper we study the effects of rotation in low-mass, low-metallicity RGB stars. Methods. We present the first evolutionary models taking into account self-consistently the latest prescriptions for the transport of angular momentum by meridional circulation and shear turbulence in stellar interiors as well as the associated mixing processes for chemicals computed from the ZAMS to the upper RGB. We discuss the uncertainties associated with the physical description of the rotational mixing in detail and carefully study their effects on the rotation profile, diffusion coefficients, structural evolution, lifetimes, and chemical signatures at the stellar surface. We focus in particular on the various assumptions concerning the rotation law in the convective envelope, the initial rotation velocity distribution, the presence of μ -gradients, and the treatment of the horizontal and vertical turbulence. Results. This exploration leads to two main conclusions. (1) After completion of the first dredge-up, the degree of differential rotation (and hence mixing) is maximised in the case of a differentially rotating convective envelope (i.e., $j_{{\rm CE}}(r) = {\rm const.}$), as anticipated in previous studies. (2) Even with this assumption, and contrary to some previous claims, the present treatment for the evolution of the rotation profile and associated meridional circulation and shear turbulence does not lead to enough mixing of chemicals to explain the abundance anomalies in low-metallicity field and globular cluster RGB stars observed around the bump  luminosity. Conclusions. This study raises questions that need to be addressed in the near future. These include, for example, the interaction between rotation and convection and the trigger of additional hydrodynamical instabilities.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/3c64623db8ab538bf33cd01374a28082ce4e1abe

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In Astronomy and Astrophysics

1. A. Karakas
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4. M. Limongi
5. A. Miglio
6. J. Lattanzio
7. Matteo Cantiello
8. S. Cristallo

Citations in the corpus

• Thermohaline instability and rotation-induced mixing I. Low- and intermediate-mass solar metallicity stars up to the end of the AGB (2010, methodology): “After the completion of the first dredge-up, both standard and recent rotating models (Chanamé et al. 2005; Palacios et al. 2006) predict no further 1 By canonical we refer to the modelling of non-rotating, nonmagnetic stars, in which convection is the only mechanism that drives mixing in stellar…”
• Chemical evolution with rotating massive star yields - I. The solar neighbourhood and the s-process elements (2018, methodology): “15 the effect of the FDU for higher initial metallicities, and a solar initial 12C/13C: for [Fe/H]= −1.5 and a 0.85 M star calculated by Palacios et al. (2006) and for [Fe/H]= 0 a 2 M star calculated by us.”
• Improved angular momentum evolution model for solar-like stars II. Exploring the mass dependence (2015, unknown): “…and the redistribution of angular momentum in the stellar interior at all phases of evolution (MacGregor & Brenner 1991; Allain 1998; Talon & Charbonnel 2003, 2005; Palacios et al. 2003, 2006; Charbonnel & Talon 2005; Charbonnel & Lagarde 2010; Lagarde et al. 2011, 2012; Charbonnel et al. 2013).”
• Thermohaline mixing: a physical mechanism governing the photospheric composition of low-mass giants (2007, methodology): “It is two to three orders of magnitude higher than that characterizing the rotational mixing (Palacios et al. 2006).”
• ANGULAR MOMENTUM TRANSPORT WITHIN EVOLVED LOW-MASS STARS (2014, background): “The nature of this mixing is currently debated (See e.g. Palacios et al. 2006; Charbonnel & Zahn 2007; Nordhaus et al. 2008; Cantiello & Langer 2010; Traxler et al. 2011; Denissenkov & Merryfield 2011; Brown et al. 2013).”
• Thermohaline instability and rotation-induced mixing - III. Grid of stellar models and asymptotic asteroseismic quantities from the pre-main sequence up to the AGB for low- and intermediate-mass stars of various metallicities (2012, background): “This hypothesis leads to a minimum shear-mixing approach in the underlying radiative layers, as discussed in Palacios et al. (2006) and Brun & Palacios (2009).”
• Angular momentum transport in stellar interiors constrained by rotational splittings of mixed modes in red giants (2012, background): “As expected from previous computations of rotating models including shellular rotation, the rotation profile during the red giant phase is very steep as a result of the central contraction occurring at the end of the main sequence (Palacios et al. 2006; Eggenberger et al. 2010c).”
• Seismic diagnostics for transport of angular momentum in stars. I. Rotational splittings from the pre-main sequence to the red-giant branch. (2012, background): “D numerical simulations suggest instead a prescription of uniform specific angular momentum (e. g. Denissenkov & Tout 2000; Palacios et al. 2006).”
• Stellar Models and Yields of Asymptotic Giant Branch Stars (2007, background): “While the physical mechanism for the extramixing is unknown3 it is commonly thought to be rotation (e.g. Palacios et al. 2006), although we also refer to the mixing recently discovered by Eggleton et al. (2006) and investigated further by Eggleton et al. (2007) and Charbonnel & Zahn (2007).”