Angular momentum transport by magnetic fields in main sequence stars with Gamma Doradus pulsators

Context. Asteroseismic studies showed that cores of post main-sequence stars rotate slower than theoretically predicted by stellar models with purely hydrodynamical transport processes. Recent studies on main sequence stars, particularly Gamma Doradus ($\gamma$ Dor) stars, revealed their internal rotation rate for hundreds of stars, offering a counterpart on the main sequence for studies of angular momentum transport. Aims. We investigate whether such a disagreement between observed and predicted internal rotation rates is present in main sequence stars by studying angular momentum transport in $\gamma$ Dor stars. Furthermore, we test whether models of rotating stars with internal magnetic fields can reproduce their rotational properties. Methods. We compute rotating models with the Geneva stellar evolution code taking into account meridional circulation and the shear instability. We also compute models with internal magnetic fields using a general formalism for transport by the Tayler-Spruit dynamo. We then compare these models to observational constraints for $\gamma$ Dor stars that we compiled from the literature, combining so the core rotation rates, projected rotational velocities from spectroscopy, and constraints on their fundamental parameters. Results. We show that combining the different observational constraints available for $\gamma$ Dor stars enable to clearly distinguish the different scenarios for internal angular momentum transport. Stellar models with purely hydrodynamical processes are in disagreement with the data whereas models with internal magnetic fields can reproduce both core and surface constraints simultaneously. Conclusions. Similarly to results obtained for subgiant and red giant stars, angular momentum transport in radiative regions of $\gamma$ Dor stars is highly efficient, in good agreement with predictions of models with internal magnetic fields.Comment: Accepted for publication in Astronomy & Astrophysics. 16 pages, 17 figures, 1 appendi

Weighing stars from birth to death: mass determination methods across the HRD

The mass of a star is the most fundamental parameter for its structure, evolution, and final fate. It is particularly important for any kind of stellar archaeology and characterization of exoplanets. There exist a variety of methods in astronomy to estimate or determine it. In this review we present a significant number of such methods, beginning with the most direct and model-independent approach using detached eclipsing binaries. We then move to more indirect and model-dependent methods, such as the quite commonly used isochrone or stellar track fitting. The arrival of quantitative asteroseismology has opened a completely new approach to determine stellar masses and to complement and improve the accuracy of other methods. We include methods for different evolutionary stages, from the pre-main sequence to evolved (super)giants and final remnants. For all methods uncertainties and restrictions will be discussed. We provide lists of altogether more than 200 benchmark stars with relative mass accuracies between [0.3,2]% for the covered mass range of M∈[0.1,16]M⊙, 75% of which are stars burning hydrogen in their core and the other 25% covering all other evolved stages. We close with a recommendation how to combine various methods to arrive at a “mass-ladder” for stars.Instituto de Astrofísica de La Plat

Probability distributions of initial rotation velocities and core-boundary mixing efficiencies of γ Doradus stars

International audienceContext. The theory of rotational and chemical evolution is incomplete, thereby limiting the accuracy of model-dependent stellar mass and age determinations. The γ Doradus (γ Dor) pulsators are excellent points of calibration for the current state-of-the-art stellar evolution models, as their gravity modes probe the physical conditions in the deep stellar interior. Yet, individual asteroseismic modelling of these stars is not always possible because of insufficient observed oscillation modes.Aims. This paper presents a novel method to derive distributions of the stellar mass, age, core-boundary mixing efficiency, and initial rotation rates for γ Dor stars.Methods. We computed a grid of rotating stellar evolution models covering the entire γ Dor instability strip. We then used the observed distributions of the luminosity, effective temperature, buoyancy travel time, and near-core rotation frequency of a sample of 539 stars to assign a statistical weight to each of our models. This weight is a measure of how likely the combination of a specific model is. We then computed weighted histograms to derive the most likely distributions of the fundamental stellar properties.Results. We find that the rotation frequency at zero-age main sequence follows a normal distribution, peaking at around 25% of the critical Keplerian rotation frequency. The probability-density function for extent of the core-boundary mixing zone, given by a factor of fCBM times the local pressure scale height (assuming an exponentially decaying parameterisation), decreases linearly with increasing fCBM.Conclusions. Converting the distribution of fractions of critical rotation at the zero-age main sequence to units of d−1, we find most F-type stars start the main sequence with a rotation frequency between 0.5 d−1 and 2 d−1. Regarding the core-boundary mixing efficiency, we find that it is generally weak in this mass regime

Sensitivity of gravito-inertial modes to differential rotation in intermediate-mass main-sequence stars

Context. While rotation has a major impact on stellar structure and evolution, its effects are not well understood. Thanks to high-quality and long-time base photometric observations obtained with recent space missions, we are now able to study stellar rotation more precisely. Aims. We aim to constrain radial differential rotation profiles in γ Doradus (γ Dor) stars, and to develop new theoretical seismic diagnosis for such stars with rapid and potentially non-uniform rotation. Methods. We have derived a new asymptotic description which accounts for the impact of weak differential near-core rotation on gravity-mode period spacings. The theoretical predictions are illustrated from pulsation computations with the code GYRE and compared with observations of γ Dor stars. When possible, we also derived the surface rotation rates in these stars by detecting and analysing signatures of rotational modulation, and computed the core-to-surface rotation ratios. Results. Stellar rotation must be strongly differential before its effects on period spacing patterns can be detected, unless multiple period spacing patterns can be compared. Six stars in our sample exhibit a single unexplained period spacing pattern of retrograde modes. We hypothesise that these are Yanai modes. Finally, we find signatures of rotational spot modulation in the photometric data of eight targets. Conclusions. If only one period spacing pattern is detected and analysed for a star, it is difficult to detect differential rotation. A rigidly rotating model will often provide the best solution. Differential rotation can only be detected when multiple period spacing patterns have been found for a single star or its surface rotation rate is known as well. This is the case for eight of the stars in our sample, revealing surface-to-core rotation ratios between 0.95 and 1.05

Applying an ecosystem approach to explore modifiable factors related to the risk for low motor competence in young children

Objectives: Early childhood is a crucial phase for motor development in which differences between children can manifest. These differences might be related to factors in ecosystems in which children are raised, of which little is currently known. The current study's purpose was to explore which modifiable factors in children's ecosystems are associated with the odds for low versus higher motor competence (MC) in 4- to 6-year-old children. Design: A cross-sectional study design was conducted to investigate which modifiable social and physical factors in the home environment and direct living environment were associated with differences in MC. Methods: Children's MC was measured through the Athletic Skills Track in 612 4- to 6-year-olds, from 10 primary schools in Eindhoven, the Netherlands. Parenting practices, characteristics of the home environment, and perceptions of the direct living environment were assessed through parental questionnaires. Hierarchical logistic regression analyses were conducted to evaluate factors associated with low MC in children. Results: The presence of a garden at home and higher perceived sports facilities in the direct living environment decreased the likelihood of children being classified as low MC. Moreover, stronger parental active transportation routines and more discouraging physical activity parenting practices resulted in lower odds of low MC. In addition, girls were more at risk for low MC. Conclusions: Characteristics of the social and physical home environment and direct living environment were associated with MC disparities during early childhood. Both parenting practices and parental physical activity-involved behaviours are relevant modifiable factors related to differences in children's MC

Applying an ecosystem approach to explore modifiable factors related to the risk for low motor competence in young children

OBJECTIVES: Early childhood is a crucial phase for motor development in which differences between children can manifest. These differences might be related to factors in ecosystems in which children are raised, of which little is currently known. The current study's purpose was to explore which modifiable factors in children's ecosystems are associated with the odds for low versus higher motor competence (MC) in 4- to 6-year-old children. DESIGN: A cross-sectional study design was conducted to investigate which modifiable social and physical factors in the home environment and direct living environment were associated with differences in MC. METHODS: Children's MC was measured through the Athletic Skills Track in 612 4- to 6-year-olds, from 10 primary schools in Eindhoven, the Netherlands. Parenting practices, characteristics of the home environment, and perceptions of the direct living environment were assessed through parental questionnaires. Hierarchical logistic regression analyses were conducted to evaluate factors associated with low MC in children. RESULTS: The presence of a garden at home and higher perceived sports facilities in the direct living environment decreased the likelihood of children being classified as low MC. Moreover, stronger parental active transportation routines and more discouraging physical activity parenting practices resulted in lower odds of low MC. In addition, girls were more at risk for low MC. CONCLUSIONS: Characteristics of the social and physical home environment and direct living environment were associated with MC disparities during early childhood. Both parenting practices and parental physical activity-involved behaviours are relevant modifiable factors related to differences in children's MC

Dynamical parallax, physical parameters, and evolutionary status of the components of the bright eclipsing binary alpha Draconis

Aims. Both components of the bright eclipsing binary a Dra have been resolved using long baseline interferometry and the secondary component has been shown to contribute approximately 15% of the total flux; however, a spectroscopic detection of the companion star has so far been unsuccessful. We aim for a firm spectroscopic detection of the secondary component of alpha Dra using state-of-the-art spectroscopic analysis methods for very high-quality spectroscopic observations. This will allow the determination of fundamental and atmospheric properties of the components in the system with high precision and accuracy

Forward Asteroseismic Modeling of Stars with a Convective Core from Gravity-mode Oscillations: Parameter Estimation and Stellar Model Selection

International audienc