Completion of the mixed unit interval graphs hierarchy

Talon, Alexandre; Kratochvíl, Jan

doi:10.1002/jgt.22159

Cited by 14 publications

(17 citation statements)

References 10 publications

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“…Rotation has been shown to impact not only the stellar structure by perturbing the hydrostatic equilibrium, but also the internal dynamics of stars by means of the transport of both angular momentum and A&A proofs: manuscript no. article_GEHAN chemical species (Zahn 1992;Talon & Zahn 1997;Lagarde et al 2012). It is thus crucial to measure this parameter for a large number of stars to monitor its effect on stellar evolution (Lagarde et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Core rotation braking on the red giant branch for various mass ranges

Gehan

Mosser

Michel

et al. 2018

A&A

172

267

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Context. Asteroseismology allows us to probe stellar interiors. In the case of red giant stars, conditions in the stellar interior are such to allow for the existence of mixed modes, consisting in a coupling between gravity waves in the radiative interior and pressure waves in the convective envelope. Mixed modes can thus be used to probe the physical conditions in red giant cores. However, we still need to identify the physical mechanisms that transport angular momentum inside red giants, leading to the slow-down observed for the red giant core rotation. Thus large-scale measurements of the red giant core rotation are of prime importance to obtain tighter constraints on the efficiency of the internal angular momentum transport, and to study how this efficiency changes with stellar parameters. Aims. This work aims at identifying the components of the rotational multiplets for dipole mixed modes in a large number of red giant oscillation spectra observed by Kepler. Such identification provides us with a direct measurement of the red giant mean core rotation. Methods. We compute stretched spectra that mimic the regular pattern of pure dipole gravity modes. Mixed modes with same azimuthal order are expected to be almost equally spaced in stretched period, with a spacing equals to the pure dipole gravity mode period spacing. The departure from this regular pattern allows us to disentangle the various rotational components and therefore to determine the mean core rotation rates of red giants. Results. We automatically identify the rotational multiplet components of 1183 stars on the red giant branch with a success rate of 69% with respect to our initial sample. As no information on the internal rotation can be deduced for stars seen pole-on, we obtain mean core rotation measurements for 875 red giant branch stars. This large sample includes stars with a mass as large as 2.5 M , allowing us to test the dependence of the core slow-down rate on the stellar mass. Conclusions. Disentangling rotational splittings from mixed modes is now possible in an automated way for stars on the red giant branch, even for the most complicated cases, where the rotational splittings exceed half the mixed-mode period spacing. This work on a large sample allows us to refine previous measurements of the evolution of the mean core rotation on the red giant branch. Rather than a slight slow down, our results suggest rotation to be constant along the red giant branch, with values independent on the mass.

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Section: Introductionmentioning

confidence: 99%

Core rotation braking on the red giant branch for various mass ranges

Gehan

Mosser

Michel

et al. 2018

A&A

172

267

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show abstract

“…It will be interesting to determine, through further DNSs, which aspects of the model remain valid and which ones do not when the Péclet number is large (see Prat & Lignières 2013, 2014Garaud & Kulenthirarajah 2016, for preliminary analyses of this question). Finally, many other additional effects could radically alter the predictions for mixing by diffusive shear flows, such as lateral shear (Talon & Zahn 1997), compositional gradients (Maeder 1997;Prat & Lignières 2014), and of course, magnetic fields (e.g. Acheson & Gibbons 1978).…”

Section: Discussionmentioning

confidence: 99%

Turbulent Transport by Diffusive Stratified Shear Flows: From Local to Global Models. II. Limitations of Local Models

Gagnier

Garaud

2018

ApJ

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This paper continues the systematic investigation of diffusive shear instabilities initiated in Part I of this series. In this work, we primarily focus on quantifying the impact of non-local mixing, which is not taken into account in Zahn's mixing model (Zahn 1992). We present the results of direct numerical simulations in a new model setup designed to contain coexisting laminar and turbulent shear layers. As in Part I, we use the Low Péclet Number approximation of Lignières (1999) to model the evolution of the perturbations. Our main findings are twofold. First, turbulence is not necessarily generated whenever Zahn's nonlinear criterion (Zahn 1974) JPr < (JPr) c is satisfied, where J = N 2 /S 2 is the local gradient Richardson number, Pr = ν/κ T is the Prandtl number, and (JPr) c 0.007. We have demonstrated that the presence or absence of turbulent mixing in this limit hysteretically depends on the history of the shear layer. Second, Zahn's nonlinear instability criterion only approximately locates the edge of the turbulent layer, and mixing beyond the region where JPr < (JPr) c can also take place in a manner analogous to convective overshoot. We found that the turbulent kinetic energy decays roughly exponentially beyond the edge of the shear-unstable region, on a lengthscale δ that is directly proportional to the scale of the turbulent eddies, which are themselves of the order of the Zahn scale (see Part I). Our results suggest that mixing by diffusive shear instabilities should be modeled with more care than is currently standard in stellar evolution codes.

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“…is the diffusion coefficient due to the shear instability. We use the formulation by Talon & Zahn (1997)…”

Section: Transport Of Angular Momentummentioning

confidence: 99%

Mixing by overshooting and rotation in intermediate-mass stars

Costa

Girardi

Bressan

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Double-line eclipsing binaries (DLEBs) have been recently used to constrain the amount of central mixing as a function of stellar mass, with contrasting results. In this work, we reanalyze the DLEB sample by Claret & Torres, using a Bayesian method and new PARSEC tracks that account for both convective core overshooting and rotational mixing. Using overshooting alone we obtain that, for masses larger than about 1.9 M , the distribution of the overshooting parameter, λ ov , has a wide dispersion between 0.3 and 0.8, with essentially no values below λ ov = 0.3 -0.4. While the lower limit supports a mild convective overshooting efficiency, the large dispersion derived is difficult to explain in the framework of current models of that process, which leave little room for large randomness. We suggest that a simple interpretation of our results can be rotational mixing: different initial rotational velocities, in addition to a fixed amount of overshooting, could reproduce the high dispersion derived for intermediatemass stars. After a reanalysis of the data, we find good agreement with models computed with fixed overshooting parameter, λ ov = 0.4, and initial rotational rates, ω, uniformly distributed in a wide range between 0 and 0.8 times the break-up value, at varying initial mass. We also find that our best-fitting models for the components of α Aurigae and TZ Fornacis, agree with their observed rotational velocities, thus providing independent support to our hypothesis. We conclude that a constant efficiency of overshooting in concurrence with a star-to-star variation in the rotational mixing, might be crucial in the interpretation of such data.

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Completion of the mixed unit interval graphs hierarchy

Abstract: We describe the missing class of the hierarchy of mixed unit interval graphs. This class is generated

Cited by 14 publications

References 10 publications

Core rotation braking on the red giant branch for various mass ranges

Core rotation braking on the red giant branch for various mass ranges

Turbulent Transport by Diffusive Stratified Shear Flows: From Local to Global Models. II. Limitations of Local Models

Mixing by overshooting and rotation in intermediate-mass stars

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