Theory of stellar convection: removing the mixing-length parameter

Pasetto, Stefano; Chiosi, C.; Cropper, Mark; Grebel, Eva K.

doi:10.1093/mnras/stu1933

Cited by 26 publications

(110 citation statements)

References 22 publications

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“…By fixing the mixing length of the FST model to be the distance to the top of the convection zone, Canuto & Mazzitelli (1991) found they were able to produce a viable solar model without recourse to free parameters. More recently, Pasetto et al (2014) have also produced a parameter-free theory of convection, but it has yet to be tested in full stellar evolution models. Most recently, Arnett et al (2015) have produced a 1D convective theory based on 3D hydrodynamical simulations of convection.…”

Section: Discussionmentioning

confidence: 99%

Confronting uncertainties in stellar physics

Stancliffe

Fossati

Passy

et al. 2016

A&A

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We assess the systematic uncertainties in stellar evolutionary calculations for low-to intermediate-mass, main-sequence stars. We compare published stellar tracks from several different evolution codes with our own tracks computed using the stellar codes stars and mesa. In particular, we focus on tracks of 1 and 3 M at solar metallicity. We find that the spread in the available 1 M tracks (computed before the recent solar composition revision) can be covered by tracks between 0.97−1.01 M computed with the stars code. We assess some possible causes of the origin of this uncertainty, including how the choice of input physics and the solar constraints used to perform the solar calibration affect the tracks. We find that for a 1 M track, uncertainties of around 10% in the initial hydrogen abundance and initial metallicity produce around a 2% error in mass. For the 3 M tracks, there is very little difference between the tracks from the various different stellar codes. The main difference comes in the extent of the main sequence, which we believe results from the different choices of the implementation of convective overshooting in the core. Uncertainties in the initial abundances lead to a 1−2% error in the mass determination. These uncertainties cover only part of the total error budget, which should also include uncertainties in the input physics (e.g., reaction rates, opacities, convective models) and any missing physics (e.g., radiative levitation, rotation, magnetic fields). Uncertainties in stellar surface properties such as luminosity and effective temperature will further reduce the accuracy of any potential mass determinations.

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Section: Discussionmentioning

confidence: 99%

Confronting uncertainties in stellar physics

Stancliffe

Fossati

Passy

et al. 2016

A&A

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“…The non-local, time-dependent convective models (see, e.g., Xiong 1979Xiong , 1989Canuto 2011aCanuto , 2011bZhang & Li 2012b;Zhang 2013Zhang , 2016Pasetto et al 2014Pasetto et al , 2015Arnett et al 2015) may be able to provide better insight into the physical structure of the overshoot region, and allow us to improve the fit to the observed period spacing of g-mode pulsators. Therefore, the long series of dipole period spacing in KIC 7760680 and Star I provides two ideal tests for theories of convective and nonconvective heat, as well as chemical and angular momentum transport.…”

Section: Mode Trapping In the Deep Stellar Interiormentioning

confidence: 99%

Sub-Inertial Gravity Modes in the B8v Star Kic 7760680 Reveal Moderate Core Overshooting and Low Vertical Diffusive Mixing

Moravveji

Townsend

Aerts

et al. 2016

ApJ

163

273

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Thus far, KIC 7760680 is the richest slowly pulsating B star, exhibiting 36 consecutive dipole (ℓ = 1) gravity (g-) modes. The monotonically decreasing period spacing of the series, in addition to the local dips in the pattern, confirm that KIC 7760680 is a moderate rotator with clear mode trapping in chemically inhomogeneous layers. We employ the traditional approximation of rotation to incorporate rotational effects on g-mode frequencies. Our detailed forward asteroseismic modeling of this g-mode series reveals that KIC 7760680 is a moderately rotating B star with mass ∼3.25 M e . By simultaneously matching the slope of the period spacing and the number of modes in the observed frequency range, we deduce that the equatorial rotation frequency of KIC 7760680 is 0.4805 day −1 , which is 26% of its Roche break up frequency. The relative deviation of the model frequencies and those observed is less than 1%. We succeed in tightly constraining the exponentially decaying convective core overshooting parameter to f ov ≈ 0.024 ± 0.001. This means that convective core overshooting can coexist with moderate rotation. Moreover, models with exponentially decaying overshoot from the core outperform those with the classical step-function overshoot. The best value for extra diffusive mixing in the radiatively stable envelope is confined to »  D log 0.75 0.25 ext (with D ext in cm 2 s −1 ), which is notably smaller than theoretical predictions.

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“…A relation between pre-and post-shock pressure to account for this isentropic compression was already worked out in Appendix A.3 of Paper I. . This was already suggested in Paper I and extensively considered in a different context in Pasetto et al (2014). For v = 0 ∧ η 0, this reduces to the Eq.…”

Section: Resultsmentioning

confidence: 69%

Environmental effects on star formation in dwarf galaxies and star clusters

Pasetto

Cropper

Fujita

et al. 2014

A&A

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Context. The role of the environment in the formation of a stellar population is a difficult problem in astrophysics. The reason is that similar properties of a stellar population are found in star systems embedded in different environments or, vice versa, similar environments contain stellar systems with stellar populations having different properties. Aims. In this paper, we develop a simple analytical criterion to investigate the role of the environment on the onset of star formation. We will consider the main external agents that influence star formation (i.e. ram pressure, tidal interaction, Rayleigh-Taylor and Kelvin-Helmholtz instabilities) in a spherical galaxy moving through an external environment. The theoretical framework developed here has direct applications to the cases of dwarf galaxies in galaxy clusters and dwarf galaxies orbiting our Milky Way system, as well as any primordial gas-rich cluster of stars orbiting within its host galaxy. Methods. We develop an analytic formalism to solve the fluid dynamics equations in a non-inertial reference frame mapped with spherical coordinates. The two-fluids instability at the interface between a stellar system and its surrounding hotter and less dense environment is related to the star formation processes through a set of differential equations. The solution presented here is quite general, allowing us to investigate most kinds of orbits allowed in a gravitationally bound system of stars in interaction with a major massive companion. Results. We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system (as a dwarf galaxy or a globular cluster) on its surrounding environment useful in theoretical interpretations of numerical results as well as observational applications. We show how spherical coordinates naturally enlighten the interpretation of two-fluids instability in a geometry that directly applies to an astrophysical case. This criterion predicts the threshold value for the onset of star formation in a mass vs. size space for any orbit of interest. Moreover, we show for the first time the theoretical dependencies of the different instability phenomena acting on a system in a fully analytical way.

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Theory of stellar convection: removing the mixing-length parameter

Cited by 26 publications

References 22 publications

Confronting uncertainties in stellar physics

Confronting uncertainties in stellar physics

Sub-Inertial Gravity Modes in the B8v Star Kic 7760680 Reveal Moderate Core Overshooting and Low Vertical Diffusive Mixing

Environmental effects on star formation in dwarf galaxies and star clusters

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