Chemical Transport and Spontaneous Layer Formation in Fingering Convection in Astrophysics

Brown, Justin M.; Garaud, Pascale; Stellmach, Stephan

doi:10.1088/0004-637x/768/1/34

Cited by 121 publications

(399 citation statements)

References 35 publications

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“…An empirically derived value of Ct = 1000 can reproduce abundance patterns in both globular cluster stars (Angelou et al 2011(Angelou et al , 2012 and field stars (Charbonnel & Lagarde 2010) as well as the dichotomy between carbon-normal and carbon-enhanced metalpoor stars ). Denissenkov (2010) and Cantiello & Langer (2010) prefer a lower value of Ct = 12 on theoretical grounds, which is also supported by 3D hydrodynamical models that suggest the mixing is inefficient on the RGB (Denissenkov & Merryfield 2011;Traxler, Garaud & Stellmach 2011;Brown, Garaud & Stellmach 2013). Parametrising extra mixing in this form and comparing to observations can still tell us much about the transport of material in the stars.…”

Section: Overview Of the Stellar Modelsmentioning

confidence: 63%

Diagnostics of stellar modelling from spectroscopy and photometry of globular clusters

Angelou

D’Orazi

Constantino

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We conduct a series of comparisons between spectroscopic and photometric observations of globular clusters and stellar models to examine their predictive power. Data from medium-to-high resolution spectroscopic surveys of lithium allow us to investigate first dredge-up and extra mixing in two clusters well separated in metallicity. Abundances at first dredge-up are satisfactorily reproduced but there is preliminary evidence to suggest that the models overestimate the luminosity at which the surface composition first changes in the lowest-metallicity system. Our models also begin extra mixing at luminosities that are too high, demonstrating a significant discrepancy with observations at low metallicity. We model the abundance changes during extra mixing as a thermohaline process and determine that the usual diffusive form of this mechanism cannot simultaneously reproduce both the carbon and lithium observations. Hubble Space Telescope photometry provides turnoff and bump magnitudes in a large number of globular clusters and offers the opportunity to better test stellar modelling as function of metallicity. We directly compare the predicted main-sequence turn-off and bump magnitudes as well as the distance-independent parameter ∆M V MSTO bump . We require 15 Gyr isochrones to match the main-sequence turn-off magnitude in some clusters and cannot match the bump in low-metallicity systems. Changes to the distance modulus, metallicity scale and bolometric corrections may impact on the direct comparisons but ∆M V MSTO bump , which is also underestimated from the models, can only be improved through changes to the input physics. Overshooting at the base of the convective envelope with an efficiency that is metallicity dependent is required to reproduce the empirically determined value of ∆M V MSTO bump .

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Section: Overview Of the Stellar Modelsmentioning

confidence: 63%

Diagnostics of stellar modelling from spectroscopy and photometry of globular clusters

Angelou

D’Orazi

Constantino

et al. 2015

Monthly Notices of the Royal Astronomical Society

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“…Here we used the recent prescription given by Brown et al (2013), which has been confirmed by the 3D simulations of Zemskova et al 2014.…”

Section: Computations Of Fingering Convectionmentioning

confidence: 99%

Accretion of planetary matter and the lithium problem in the 16 Cygni stellar system

Deal

Richard

Vauclair

2015

A&A

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Context. The 16 Cygni system is composed of two solar analogues with similar masses and ages. A red dwarf is in orbit around 16 Cygni A, and 16 Cygni B hosts a giant planet. The abundances of heavy elements are similar in the two stars, but lithium is much more depleted in 16 Cygni B than in 16 Cygni A, by a factor of at least 4.7. Aims. The interest of studying the 16 Cygni system is that the two star have the same age and the same initial composition. The differences currently observed must be due to their different evolution, related to the fact that one of them hosts a planet while the other does not. Methods. We computed models of the two stars that precisely fit the observed seismic frequencies. We used the Toulouse Geneva Evolution Code (TGEC), which includes complete atomic diffusion (including radiative accelerations). We compared the predicted surface abundances with the spectroscopic observations and confirm that another mixing process is needed. We then included the effect of accretion-induced fingering convection. Results. The accretion of planetary matter does not change the metal abundances but leads to lithium destruction, which depends upon the accreted mass. A fraction of the Earth's mass is enough to explain the lithium surface abundances of 16 Cygni B. We also checked the beryllium abundances. Conclusions. In the case of accretion of heavy matter onto stellar surfaces, the accreted heavy elements do not remain in the outer convective zones, but are mixed downwards by fingering convection induced by the unstable μ-gradient. Depending on the accreted mass, this mixing process may transport lithium down to its nuclear destruction layers and lead to an extra lithium depletion at the surface. A fraction of the Earth's mass is enough to explain a lithium ratio of 4.7 in the 16 Cygni system. In this case beryllium is not destroyed. Such a process may be frequent in planet-hosting stars and should be studied in other cases in the future.

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“…Hydrodynamic simulations in 2D and 3D have been used to improve the constraints on the efficiency of thermohaline instability in stellar interiors (Denissenkov et al 2009;Denissenkov 2010;Denissenkov & Merryfield 2011;Rosenblum et al 2011;Traxler et al 2011;Brown et al 2013). These simulations currently show that double diffusive instability is not efficient enough to significantly change surface abundances (Wachlin et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints

Lagarde

Miglio

Eggenberger

et al. 2015

A&A

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Context. The availability of asteroseismic constraints for a large sample of red giant stars from the CoRoT and Kepler missions paves the way for various statistical studies of the seismic properties of stellar populations. Aims. We use a detailed spectroscopic study of 19 CoRoT red giant stars to compare theoretical stellar evolution models to observations of the open cluster NGC 6633 and field stars. Methods. In order to explore the effects of rotation-induced mixing and thermohaline instability, we compare surface abundances of carbon isotopic ratio and lithium with stellar evolution predictions. These chemicals are sensitive to extra-mixing on the red giant branch. Results. We estimate mass, radius, and distance for each star using the seismic constraints. We note that the Hipparcos and seismic distances are different. However, the uncertainties are such that this may not be significant. Although the seismic distances for the cluster members are self consistent they are somewhat larger than the Hipparcos distance. This is an issue that should be considered elsewhere. Models including thermohaline instability and rotation-induced mixing, together with the seismically determined masses can explain the chemical properties of red giant targets. However, with this sample of stars we cannot perform stringent tests of the current stellar models. Tighter constraints on the physics of the models would require the measurement of the core and surface rotation rates, and of the period spacing of gravity-dominated mixed modes. A larger number of stars with longer times series, as provided by Kepler or expected with Plato, would help ensemble asteroseismology.

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Chemical Transport and Spontaneous Layer Formation in Fingering Convection in Astrophysics

Cited by 121 publications

References 35 publications

Diagnostics of stellar modelling from spectroscopy and photometry of globular clusters

Diagnostics of stellar modelling from spectroscopy and photometry of globular clusters

Accretion of planetary matter and the lithium problem in the 16 Cygni stellar system

Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints

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