scholarly journals ANGULAR MOMENTUM TRANSPORT WITHIN EVOLVED LOW-MASS STARS

2014 ◽  
Vol 788 (1) ◽  
pp. 93 ◽  
Author(s):  
Matteo Cantiello ◽  
Christopher Mankovich ◽  
Lars Bildsten ◽  
Jørgen Christensen-Dalsgaard ◽  
Bill Paxton
Keyword(s):  
Angular Momentum ◽  
Momentum Transport ◽  
Low Mass Stars ◽  
Angular Momentum Transport ◽  
Low Mass

scholarly journals Transport of angular momentum in solar-like oscillating stars

2013 ◽  
Vol 9 (S301) ◽  
pp. 161-168
Author(s):  
Mariejo Goupil ◽  
Sébastien Deheuvels ◽  
Joao Marques ◽  
Yveline Lebreton ◽  
Benoit Mosser ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Space Missions ◽  
Momentum Transport ◽  
Current Understanding ◽  
Red Giants ◽  
The Sun ◽  
Low Mass Stars ◽  
Angular Momentum Transport ◽  
Low Mass

AbstractOur current understanding and modeling of angular momentum transport in low-mass stars are briefly reviewed. Emphasis is set on single stars slightly younger that the Sun and on subgiants and red giants observed by the space missionsCoRoTandKepler.

scholarly journals First grids of low-mass stellar models and isochrones with self-consistent treatment of rotation

2019 ◽  
Vol 631 ◽  
pp. A77 ◽  
Author(s):  
L. Amard ◽  
A. Palacios ◽  
C. Charbonnel ◽  
F. Gallet ◽  
C. Georgy ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Open Clusters ◽  
Momentum Transport ◽  
Surface Boundary ◽  
Angular Momentum Transport ◽  
Solar Composition ◽  
Self Consistent ◽  
Low Mass ◽  
Stellar Models ◽  
The Impact

Aims.We present an extended grid of state-of-the art stellar models for low-mass stars including updated physics (nuclear reaction rates, surface boundary condition, mass-loss rate, angular momentum transport, rotation-induced mixing, and torque prescriptions). We evaluate the impact of wind braking, realistic atmospheric treatment, rotation, and rotation-induced mixing on the structural and rotational evolution from the pre-main sequence (PMS) to the turn-off.Methods.Using the STAREVOL code, we provide an updated PMS grid. We computed stellar models for seven different metallicities, from [Fe/H] = −1 dex to [Fe/H] = +0.3 dex with a solar composition corresponding toZ = 0.0134. The initial stellar mass ranges from 0.2 to 1.5M⊙with extra grid refinement around one solar mass. We also provide rotating models for three different initial rotation rates (slow, median, and fast) with prescriptions for the wind braking and disc-coupling timescale calibrated on observed properties of young open clusters. The rotational mixing includes the most recent description of the turbulence anisotropy in stably stratified regions.Results.The overall behaviour of our models at solar metallicity, and their constitutive physics, are validated through a detailed comparison with a variety of distributed evolutionary tracks. The main differences arise from the choice of surface boundary conditions and initial solar composition. The models including rotation with our prescription for angular momentum extraction and self-consistent formalism for angular momentum transport are able to reproduce the rotation period distribution observed in young open clusters over a wide range of mass values. These models are publicly available and can be used to analyse data coming from present and forthcoming asteroseismic and spectroscopic surveys such asGaia, TESS, and PLATO.

scholarly journals The s process in AGB stars as constrained by a large sample of barium stars

2018 ◽  
Vol 620 ◽  
pp. A146 ◽  
Author(s):  
B. Cseh ◽  
M. Lugaro ◽  
V. D’Orazi ◽  
D. B. de Castro ◽  
C. B. Pereira ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Transport Mechanism ◽  
Momentum Transport ◽  
Element Abundance ◽  
Agb Stars ◽  
Primary Star ◽  
Angular Momentum Transport ◽  
Giant Stars ◽  
Low Mass ◽  
Process Elements

Context. Barium (Ba) stars are dwarf and giant stars enriched in elements heavier than iron produced by the slow neutron-capture process (s process). These stars belong to binary systems in which the primary star evolved through the asymptotic giant branch (AGB) phase. During this phase the primary star produced s-process elements and transferred them onto the secondary, which is now observed as a Ba star. Aims. We compare the largest homogeneous set of Ba giant star observations of the s-process elements Y, Zr, La, Ce, and Nd with AGB nucleosynthesis models to reach a better understanding of the s process in AGB stars. Methods. By considering the light-s (ls: Y and Zr) heavy-s (hs: La, Ce, and Nd) and elements individually, we computed for the first time quantitative error bars for the different hs-element to ls-element abundance ratios, and for each of the sample stars. We compared these ratios to low-mass AGB nucleosynthesis models. We excluded La from our analysis because the strong La lines in some of the sample stars cause an overestimation and unreliable abundance determination, as compared to the other observed hs-type elements. Results. All the computed hs-type to ls-type element ratios show a clear trend of increasing with decreasing metallicity with a small spread (less than a factor of 3). This trend is predicted by low-mass AGB models in which 13C is the main neutron source. The comparison with rotating AGB models indicates the need for the presence of an angular momentum transport mechanism that should not transport chemical species, but significantly reduces the rotational speed of the core in the advanced stellar evolutionary stages. This is an independent confirmation of asteroseismology observations of the slow down of core rotation in giant stars, and of rotational velocities of white dwarfs lower than predicted by models without an extra angular momentum transport mechanism.

scholarly journals Angular Momentum Transport and Dynamo Effect in Kepler Disks

2001 ◽  
Vol 200 ◽  
pp. 410-414
Author(s):  
Günther Rüdiger ◽  
Udo Ziegler
Keyword(s):  
Angular Momentum ◽  
Accretion Disks ◽  
Large Scale ◽  
Spherical Model ◽  
Momentum Transport ◽  
Rotational Instability ◽  
Jet Formation ◽  
Angular Momentum Transport ◽  
Dynamo Effect ◽  
Background Shear

Properties have been demonstrated of the magneto-rotational instability for two different applications, i.e. for a global spherical model and a box simulation with Keplerian background shear flow. In both nonlinear cases a dynamo operates with a negative (positive) α-effect in the northern (southern) disk hemisphere and in both cases the angular momentum transport is outwards. Keplerian accretion disks should therefore exhibit large-scale magnetic fields with a dipolar geometry of the poloidal components favoring jet formation.

scholarly journals Magnetic field transport in compact binaries

2020 ◽  
Vol 641 ◽  
pp. A133
Author(s):  
N. Scepi ◽  
G. Lesur ◽  
G. Dubus ◽  
J. Jacquemin-Ide
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Magnetic Flux ◽  
Large Scale ◽  
Compact Object ◽  
Light Curves ◽  
Momentum Transport ◽  
Local Magnetization ◽  
Angular Momentum Transport ◽  
The Impact

Context. Dwarf novæ (DNe) and low mass X-ray binaries (LMXBs) show eruptions that are thought to be due to a thermal-viscous instability in their accretion disk. These eruptions provide constraints on angular momentum transport mechanisms. Aims. We explore the idea that angular momentum transport could be controlled by the dynamical evolution of the large-scale magnetic field. We study the impact of different prescriptions for the magnetic field evolution on the dynamics of the disk. This is a first step in confronting the theory of magnetic field transport with observations. Methods. We developed a version of the disk instability model that evolves the density, the temperature, and the large-scale vertical magnetic flux simultaneously. We took into account the accretion driven by turbulence or by a magnetized outflow with prescriptions taken, respectively, from shearing box simulations or self-similar solutions of magnetized outflows. To evolve the magnetic flux, we used a toy model with physically motivated prescriptions that depend mainly on the local magnetization β, where β is the ratio of thermal pressure to magnetic pressure. Results. We find that allowing magnetic flux to be advected inwards provides the best agreement with DNe light curves. This leads to a hybrid configuration with an inner magnetized disk, driven by angular momentum losses to an MHD outflow, sharply transiting to an outer weakly-magnetized turbulent disk where the eruptions are triggered. The dynamical impact is equivalent to truncating a viscous disk so that it does not extend down to the compact object, with the truncation radius dependent on the magnetic flux and evolving as Ṁ−2/3. Conclusions. Models of DNe and LMXB light curves typically require the outer, viscous disk to be truncated in order to match the observations. There is no generic explanation for this truncation. We propose that it is a natural outcome of the presence of large-scale magnetic fields in both DNe and LMXBs, with the magnetic flux accumulating towards the center to produce a magnetized disk with a fast accretion timescale.

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