Róbert Andrássy

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About Róbert Andrássy:

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SEEK ID: https://publications.h-its.org/people/128

Location: Germany

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Joined: 24th Feb 2021

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Physics of Stellar Objects

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Heidelberg Institute for Theoretical Studies

Country: Germany

City: Heidelberg

Web page: https://www.h-its.org

Showing 5 out of a possible 10 Publications Advanced Publications list for this Person with search and filtering

Towards a self-consistent model of the convective core boundary in upper main sequence stars

Physics of Stellar Objects

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There is strong observational evidence that the convective cores of intermediate-mass and massive main sequence stars are substantially larger than those predicted by standard stellar-evolution models. …

Authors: R. Andrassy, G. Leidi, J. Higl, P. V. F. Edelmann, F. R. N. Schneider, F. K. Röpke

Date Published: 1st Mar 2024

Publication Type: Journal

DOI: 10.1051/0004-6361/202347407

Citation: A&A 683:A97

Created: 14th Mar 2024 at 14:49, Last updated: 14th Mar 2024 at 14:53

Turbulent dynamo action and its effects on the mixing at the convective boundary of an idealized oxygen-burning shell

Physics of Stellar Objects

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Convection is one of the most important mixing processes in stellar interiors. Hydrodynamic mass entrainment can bring fresh fuel from neighboring stable layers into a convection zone, modifying the …convection zone, modifying the structure and evolution of the star. Because flows in stellar convection zones are highly turbulent, multidimensional hydrodynamic simulations are fundamental to accurately capture the physics of mixing processes. Under some conditions, strong magnetic fields can be sustained by the action of a turbulent dynamo, adding another layer of complexity and possibly altering the dynamics in the convection zone and at its boundaries. In this study, we used our fully compressible S EVEN -L EAGUE H YDRO code to run detailed and highly resolved three-dimensional magnetohydrodynamic simulations of turbulent convection, dynamo amplification, and convective boundary mixing in a simplified setup whose stratification is similar to that of an oxygen-burning shell in a star with an initial mass of 25 M ⊙ . We find that the random stretching of magnetic field lines by fluid motions in the inertial range of the turbulent spectrum (i.e., a small-scale dynamo) naturally amplifies the seed field by several orders of magnitude in a few convective turnover timescales. During the subsequent saturated regime, the magnetic-to-kinetic energy ratio inside the convective shell reaches values as high as 0.33, and the average magnetic field strength is ∼10 10 G. Such strong fields efficiently suppress shear instabilities, which feed the turbulent cascade of kinetic energy, on a wide range of spatial scales. The resulting convective flows are characterized by thread-like structures that extend over a large fraction of the convective shell. The reduced flow speeds and the presence of magnetic fields with strengths up to 60% of the equipartition value at the upper convective boundary diminish the rate of mass entrainment from the stable layer by ≈20% as compared to the purely hydrodynamic case.

Authors: G. Leidi, R. Andrassy, J. Higl, P. V. F. Edelmann, F. K. Röpke

Date Published: 1st Nov 2023

Publication Type: Journal

DOI: 10.1051/0004-6361/202347621

Citation: A&A 679:A132

Created: 19th Mar 2024 at 12:26, Last updated: 19th Mar 2024 at 12:26

A finite-volume scheme for modeling compressible magnetohydrodynamic flows at low Mach numbers in stellar interiors

Physics of Stellar Objects

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Authors: G. Leidi, C. Birke, R. Andrassy, J. Higl, P. V. F. Edelmann, G. Wiest, C. Klingenberg, F. K. Röpke

Date Published: 1st Dec 2022

Publication Type: Journal

DOI: 10.1051/0004-6361/202244665

Citation: A&A 668:A143

Created: 13th Feb 2023 at 14:25, Last updated: 5th Mar 2024 at 21:25

Dynamics in a stellar convective layer and at its boundary: Comparison of five 3D hydrodynamics codes

Physics of Stellar Objects

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Authors: R. Andrassy, J. Higl, H. Mao, M. Mocák, D. G. Vlaykov, W. D. Arnett, I. Baraffe, S. W. Campbell, T. Constantino, P. V. F. Edelmann, T. Goffrey, T. Guillet, F. Herwig, R. Hirschi, L. Horst, G. Leidi, C. Meakin, J. Pratt, F. Rizzuti, F. K. Röpke, P. Woodward