Article
Astronomy & Astrophysics
Vishnu Varma, Bernhard Mueller
Summary: In the first 3D MHD simulation of convective oxygen and neon shell burning in a non-rotating star, magnetic fields in supernova progenitors were studied. The magnetic field approaches saturation levels in the oxygen shell, but does not reach kinetic equipartition.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Tanayveer S. Bhatia, Robert H. Cameron, Sami K. Solanki, Hardi Peter, Damien Przybylski, Veronika Witzke, Alexander Shapiro
Summary: This study investigates changes in stratification and convection in the near-surface convection of different spectral types of cool main-sequence stars with the inclusion of small-scale dynamo (SSD) magnetic fields. The results show that the SSD efficiently produces magnetic fields and has a significant impact on thermodynamic stratification and convective velocities, especially for F-type stars.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
J. R. Canivete Cuissa, R. Teyssier
Summary: This study conducted three-dimensional numerical simulations of magneto-hydrodynamics in stellar interiors and demonstrated the feasibility of the simulation method. The results showed an exponential growth of magnetic energy and a decrease in power of acoustic and internal gravity waves. The study highlights the importance of including magnetic fields in the study of pressure waves.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Maurizio Salaris, Santi Cassisi, Adriano Pietrinferni, Sebastian Hidalgo
Summary: This paper presents new cooling models for carbon-oxygen white dwarfs (WDs) with both H- and He-atmospheres. The models cover the whole relevant mass range and extend the updated BASTI stellar evolution archive. The core chemical stratifications are obtained from new progenitor calculations, and the physics inputs have been updated compared to previous BASTI calculations. Two sets of calculations are provided, reflecting the current uncertainty in the evaluation of the electron thermal conductivity.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Samuel Pearson, Aleks Scholz, Paula S. Teixeira, Koraljka Muzic, Victor Almendros-Abad
Summary: Based on spectroscopic observations of 68 candidates in NGC 2264, researchers confirmed 13 brown dwarfs and 19 M-type stars, with ages predominantly younger than the known cluster population, indicating distinct formation processes. The estimated total of 200-600 brown dwarfs in NGC 2264 suggests a star-to-brown dwarf ratio between 2.5:1 and 7.5:1, with a consistent substellar mass function slope of alpha = 0.43(-0.56)(+0.41) across various young clusters, indicating a uniformity in substellar mass functions within star-forming environments.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Santi Cassisi, Alexander Y. Potekhin, Maurizio Salaris, Adriano Pietrinferni
Summary: Different prescriptions for calculating conductive opacities under different degeneracy regimes have significant impacts on various stellar properties such as He-core masses, red giant branch tip luminosities, and white dwarf cooling times. Current empirical constraints are not sufficient to definitively exclude any of these alternative options. Tests against observations of faint white dwarfs in old stellar populations are needed to provide more stringent constraints.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
V. Witzke, H. B. Duehnen, A. I. Shapiro, D. Przybylski, T. S. Bhatia, R. Cameron, S. K. Solanki
Summary: Three-dimensional simulations reveal that small-scale turbulent magnetic fields have a significant impact on the surface layers of stars, especially in the case of low metallicity.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Leandro G. Althaus, Maria E. Camisassa, Santiago Torres, Tiara Battich, Alejandro H. Corsico, Alberto Rebassa-Mansergas, Roberto Raddi
Summary: Investigation of the structural and evolutionary properties of ultra-massive white dwarfs considering the effects of general relativity.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Francisco C. De Geronimo, Marcelo M. Miller Bertolami, Francisco Plaza, Marcio Catelan
Summary: This study explores the extent to which differences in micro- and macro-physics can explain the different compositions of white dwarfs found by different authors. The study also investigates the impact of these differences on the cooling times, crystallization, and pulsational properties of white dwarfs.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Maria E. Camisassa, Leandro G. Althaus, Santiago Torres, Alejandro H. Corsico, Alberto Rebassa-Mansergas, Pier-Emmanuel Tremblay, Sihao Cheng, Roberto Raddi
Summary: White dwarf stars are common end points of stellar evolution, with ultramassive white dwarfs being of special interest due to their relation to various astronomical phenomena. Recent studies suggest that some ultramassive white dwarfs exhibit a strong delay in cooling, potentially due to Ne-22 sedimentation in CO-core white dwarfs. This finding challenges standard evolutionary models and provides evidence for the existence of prolonged youth ultramassive white dwarfs.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Shin'ichirou Yoshida
Summary: Rotation affects sustainable hydrogen burning in very low-mass stellar objects due to the introduction of centrifugal force and the occurrence of rotational break-up for rapidly rotating cases. We obtained critical curves of sustainable hydrogen burning in the parameter space of mass versus central degeneracy, and observed the breaking up of the curve into two branches due to the mass-shedding limit. Based on the results, we modeled the mechano-thermal evolutions of substellar objects and studied their cooling and mass/angular momentum reductions.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Mark Lykke Winther, Victor Aguirre Borsen-Koch, Jakob Lysgaard Rorsted, Amalie Stokholm, Kuldeep Verma
Summary: With the advancement of asteroseismology, it has become possible to study the survival of convective cores within stars during their main-sequence evolution. A recent study on the star Kepler-444 found that the convective core had survived for nearly 8 Gyr, contrary to the predictions of standard stellar evolution theories. This paper aims to investigate the convective core evolution of Kepler-444 and determine its proposed longevity by modifying the input physics of stellar models and fitting the observations to the models using the BASTA pipeline. The analysis reliably constraints the convective core lifetime of Kepler-444 to be short, with a median around 0.6 Gyr and an upper bound around 3.5 Gyr.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Samuel A. Beiler, Katelyn N. Allers, Michael Cushing, Jacqueline Faherty, Mark Marley, Andrew Skemer
Summary: We conducted a spectroscopic study on eight young L dwarfs in the L-band (2.98-3.96 μm) with spectral types ranging from L2 to L7. Our analysis focused on the evolution of the Q-branch of methane absorption feature and the impact of including the L-band data on atmoshperic models. We found that the Q-branch feature first appears between L3 and L6 and that the addition of the L band causes a drop in effective temperature and requires thick clouds and higher vertical mixing rates in the models.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
F. Anzuini, A. Melatos, C. Dehman, D. Vigano, J. A. Pons
Summary: The dissipation of intense crustal electric currents can counterbalance fast cooling in neutron stars, making it difficult to infer the presence of hyperons from observed thermal luminosity. Models with and without hyperon cores both match the thermal luminosity of young and mature magnetars. Hyperon cores have little effect on the crustal temperature in magnetars, and the thermal luminosity of light and heavy magnetars are almost indistinguishable. Data from neutron stars with strong internal fields are not suitable for extracting information about the equation of state as long as hyperons are superfluid.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
F. Anzuini, A. Melatos, C. Dehman, D. Vigano, J. A. Pons
Summary: This study discusses the need for internal heating sources in neutron star models to reconcile theoretical cooling rates with observational data, focusing on moderately magnetized, isolated thermally emitting stars. By considering different internal heating mechanisms, the study finds that neutron star models can match observations of such stars through proper internal heating.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Multidisciplinary Sciences
Rakesh K. Yadav, Jeremy Bloxham
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
(2020)
Article
Geochemistry & Geophysics
T. Schwaiger, T. Gastine, J. Aubert
Summary: This passage discusses the importance of measuring length scales with both energetic and dynamic relevance in fluid dynamics. It analyzes two length scales in magnetic and non-magnetic models that achieve this dual relevance, revealing different interpretations and misrepresentations of force balance. By focusing on these scales, the study uncovers insights into the underlying mechanisms of dynamo systems and their dominant length scales.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2021)
Article
Geochemistry & Geophysics
Theo Tassin, Thomas Gastine, Alexandre Fournier
Summary: This study examines the impact of double-diffusive convection on magnetic field generation in the liquid outer core of the Earth through 3-D global geodynamo models. The findings suggest that the addition of a second buoyancy source facilitates the onset of convection and the transition between dipole-dominated and multipolar dynamos depends on the nature of the buoyancy forcing. Classical parameters expected to govern this transition fail to capture the dipole breakdown, and instead, a scale-dependent analysis of force balance is necessary to understand the dynamics.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2021)
Article
Astronomy & Astrophysics
T. Gastine, J. Wicht
Summary: The ongoing NASA's Juno mission has placed new constraints on the internal dynamics of Jupiter, revealing a complex internal structure with a dipole-dominated surface magnetic field and a stratification of metallic and molecular hydrogen. The simulations show that in Jupiter's metallic core, magnetic energy is nearly an order of magnitude larger than kinetic energy, while kinetic energy is mainly pumped into zonal flows in the molecular envelope.
Article
Computer Science, Interdisciplinary Applications
Venkatesh Gopinath, Alexandre Fournier, Thomas Gastine
Summary: This article analyzes the behavior of time integrators applied to the semi discrete problem resulting from the spectral discretization of Boussinesq thermal convection equations. Different schemes of various orders are assessed for laminar and turbulent regimes, and it is found that some high-order IMEX-RK methods exhibit occasional order reduction. Comparing with the reference integrator CNAB2, six schemes consistently outperform CNAB2 in terms of accuracy and performance. In the most turbulent setup, 13 IMEX-RK integrators outperform CNAB2 in terms of both accuracy and efficiency.
JOURNAL OF COMPUTATIONAL PHYSICS
(2022)
Article
Multidisciplinary Sciences
S. J. Bolton, S. M. Levin, T. Guillot, C. Li, Y. Kaspi, G. Orton, M. H. Wong, F. Oyafuso, M. Allison, J. Arballo, S. Atreya, H. N. Becker, J. Bloxham, S. T. Brown, L. N. Fletcher, E. Galanti, S. Gulkis, M. Janssen, A. Ingersoll, J. L. Lunine, S. Misra, P. Steffes, D. Stevenson, J. H. Waite, R. K. Yadav, Z. Zhang
Summary: Observations using the Juno spacecraft's Microwave Radiometer revealed that vortex roots in Jupiter's atmosphere extend deeper than expected condensation levels, and density inversion layers were identified. These findings provide constraints on the three-dimensional structure of Jupiter's vortices and their extension below the clouds.
Article
Geochemistry & Geophysics
Laura Kulowski, Hao Cao, Rakesh K. Yadav, Jeremy Bloxham
Summary: Using high-precision Juno gravitational measurements, the study explores Jupiter's deep atmospheric zonal flow. The research finds that most of the antisymmetric gravitational signal measured by Juno can be explained by extending observed winds to depths of around 1000 km.
JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS
(2021)
Article
Geochemistry & Geophysics
O. Barrois, T. Gastine, C. C. Finlay
Summary: This study investigates rapidly rotating convection in a thick spherical shell geometry relevant to planetary cores. The results are compared between quasi-geostrophic (QG), 3-D, and hybrid QG-3D models. The study finds that the 3-D model and QG model show similar results under strong driving, while the hybrid model and 3-D model are closer under weak driving. This research provides insights into convection patterns in planetary cores and the importance of different modeling approaches.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2022)
Article
Geosciences, Multidisciplinary
Rakesh Kumar Yadav, Hao Cao, Jeremy Bloxham
Summary: Saturn's magnetic field is highly axisymmetric, with a very small tilt angle of the magnetic dipole component. Numerical simulations suggest that small dipole tilt values can be realized by introducing spatial heat-flux variation and stably stratified layers on top of an active dynamo layer. This study presents a simplified model that achieves extremely small dipole tilt values without these ad hoc ingredients.
GEOPHYSICAL RESEARCH LETTERS
(2022)
Article
Geochemistry & Geophysics
Jeremy Bloxham, Kimberly M. Moore, Laura Kulowski, Hao Cao, Rakesh K. Yadav, David J. Stevenson, John E. P. Connerney, Scott J. Bolton
Summary: A key objective of the Juno mission is to determine the secular variation of Jupiter's internal magnetic field. This study finds that the residuals to a static model of the magnetic field are consistent with the effects of secular variation arising from zonal drift. The researchers present a technique for simultaneously inverting for the main magnetic field and the secular variation due to zonal drift, and find good agreement with previous studies. It suggests that the drift rate of Jupiter's magnetic field is steady over time periods of several decades.
JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS
(2022)
Article
Astronomy & Astrophysics
B. Zaire, L. Jouve, T. Gastine, J-F Donati, J. Morin, N. Landin, C. P. Folsom
Summary: This paper investigates the diversity of surface magnetic field configurations of cool stars using numerical simulations. The results show that dipolar solutions can exist in strongly stratified simulations, contrary to previous beliefs. The simulations resemble the outlier stars observed at Rossby numbers larger than 0.1, suggesting that the relative importance of inertial and Lorentz forces controls the dipolar to multipolar transition. Additionally, the ratio of kinetic to magnetic energies can also capture the transition in field morphology.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Mechanics
Thomas Gastine, Jonathan M. Aurnou
Summary: Convection dynamics in polar regions differ from those in lower latitudes. In spherical shell simulations, polar convection is triggered when the buoyancy forcing exceeds the critical equatorial forcing by a factor of 20. The heat transfer in polar regions increases much faster than in equatorial regions with increasing Rayleigh number. At high Rayleigh numbers, the heat fluxes in polar and equatorial regions become comparable.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Geosciences, Multidisciplinary
Rafael Lago, Thomas Gastine, Tilman Dannert, Markus Rampp, Johannes Wicht
Summary: The article discusses two parallelization schemes for the MagIC code, an open-source, high-performance pseudo-spectral code for solving magnetohydrodynamics equations. The first scheme uses MPI and OpenMP, while the second scheme involves a new two-dimensional MPI decomposition implementation. The authors also highlight algorithmic optimizations and data distribution layouts, indicating that the two-dimensional distribution configuration may be more efficient than the one-dimensional distribution.
GEOSCIENTIFIC MODEL DEVELOPMENT
(2021)
Article
Multidisciplinary Sciences
Rakesh Kumar Yadav, Moritz Heimpel, Jeremy Bloxham
Article
Astronomy & Astrophysics
Julian D. Alvarado-Gomez, Jeremy J. Drake, Cecilia Garraffo, Ofer Cohen, Katja Poppenhaeger, Rakesh K. Yadav, Sofia P. Moschou
ASTROPHYSICAL JOURNAL LETTERS
(2020)
