ORCID Profile
0000-0002-7950-0061
Current Organisations
Institute of Genetics and Developmental Biology Chinese Academy of Sciences
,
University of Sydney
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Publisher: EDP Sciences
Date: 06-2021
DOI: 10.1051/0004-6361/202140466
Abstract: Context. Asteroseismic modelling of the internal structure of main-sequence stars born with a convective core has so far been based on homogeneous analyses of space photometric Kepler light curves of four years in duration, to which most often incomplete inhomogeneously-deduced spectroscopic information was added to break degeneracies. Aims. Our goal is twofold: (1) to compose an optimal s le of gravity-mode pulsators observed by the Kepler space telescope for joint asteroseismic and spectroscopic stellar modelling, and (2) to provide spectroscopic parameters for its members, deduced in a homogeneous way. Methods. We assembled HERMES high-resolution optical spectroscopy at the 1.2 m Mercator telescope for 111 dwarfs, whose Kepler light curves allowed for the determination of their near-core rotation rates. Our spectroscopic information offers additional observational input to also model the envelope layers of these non-radially pulsating dwarfs. Results. We determined stellar parameters and surface abundances from atmospheric analysis with spectrum normalisation based on a new machine-learning tool. Our results suggest a systematic overestimation of metallicity ([M/H]) in the literature for the studied F-type dwarfs, presumably due to normalisation limitations caused by the dense line spectrum of these rotating stars. CNO surface abundances were found to be uncorrelated with the rotation properties of the F-type stars. For the B-type stars, we find a hint of deep mixing from C and O abundance ratios N abundance uncertainties are too great to reveal a correlation of N with the rotation of the stars. Conclusions. Our spectroscopic stellar parameters and abundance determinations allow for the future joint spectroscopic, astrometric ( Gaia ), and asteroseismic modelling of this legacy s le of gravity-mode pulsators, with the aim of improving our understanding of transport processes in the core-hydrogen burning phase of stellar evolution.
Publisher: Cambridge University Press (CUP)
Date: 11-2017
DOI: 10.1017/S1743921318002314
Abstract: This talk discussed the basics of gravito-inertial asteroseismology as recently developed for stars born with a convective core. Photometric space missions originally built for exoplanet hunting, notably Kepler , have opened up the low-frequency regime of stellar oscillations and revealed a larger ersity in variability than anticipated prior to the era of high-precision space photometry. The talk explained the basics of forward seismic modelling based on gravito-inertial modes, which probe the deep stellar interior. It described how a hierarchical fitting approach allows us to derive the near-core rotation period, the amount and shape of convective core overshooting, and the level of chemical mixing in the radiative envelope for stars born with a convective core and burning hydrogen in their core. A summary of the current status, covering the mass range 1.4 ≲ M ≲ 5 M ⊙ , is provided here through references to numerous recent papers.
Publisher: Oxford University Press (OUP)
Date: 13-12-2016
Publisher: American Astronomical Society
Date: 28-02-2019
Publisher: EDP Sciences
Date: 11-2021
DOI: 10.1051/0004-6361/202141572
Abstract: Context. Slowly pulsating B (SPB) stars are main-sequence multi-periodic oscillators that display non-radial gravity modes. For a fraction of these pulsators, 4-year photometric light curves obtained with the Kepler space telescope reveal period spacing patterns from which their internal rotation and mixing can be inferred. In this inference, any direct resonant mode coupling is usually ignored. Aims. We re-analyse the light curves of a s le of 38 known Kepler SPB stars. For 26 of them, the internal structure, including rotation and mixing, was recently inferred from their dipole prograde oscillation modes. Our aim is to detect direct non-linear resonant mode coupling among the largest- litude gravity modes. Methods. We extract up to 200 periodic signals per star with five different iterative pre-whitening strategies based on linear and non-linear regression applied to the light curves. We then identify candidate coupled gravity modes by verifying whether they fulfil resonant phase relations. Results. For 32 of the 38 SPB stars we find at least one candidate resonance that is detected in both the linear and the best non-linear regression model fit to the light curve and involves at least one of the two largest- litude modes. Conclusions. The majority of the Kepler SPB stars reveal direct non-linear resonances based on the largest- litude modes. These stars are thus prime targets for the non-linear asteroseismic modelling of intermediate-mass dwarfs to assess the importance of mode couplings in probing their internal physics.
Publisher: Oxford University Press (OUP)
Date: 16-08-2019
Abstract: We present the discovery of three new β Cep pulsators, three new pulsators with frequency groupings, and frequency patterns in a B3Ib star, all of which show pulsations with frequencies as high as about 17 d−1, with K2 space mission photometry. Based on a Fourier analysis and iterative pre-whitening, we present a classification and evaluate the potential for asteroseismic modelling. We include the lists of pulsation frequencies for three new β Cep pulsators, CD-28 12286, CD-27 10876, LS 3978, and additional pulsation mode frequencies for the known β Cep pulsator HD 164741. In addition, we characterize the regular frequency spacing found in the new pulsator HD 169173, and discuss its origin. We place the newly discovered variables in a colour–magnitude diagram using parallaxes from GaiaDR2 (second data release), showcasing their approximate location in the massive star domain. The identified frequency lists of these multiperiodic pulsators are a good starting point for future forward seismic modelling, after identification of at least one pulsation frequency from high-resolution time-series spectroscopy and/or multicolour photometry.
Publisher: EDP Sciences
Date: 12-2021
DOI: 10.1051/0004-6361/202142151
Abstract: Context. Multi-dimensional (magneto-)hydrodynamical simulations of physical processes in stellar interiors depend on a multitude of uncalibrated free parameters, which set the spatial and time scales of their computations. Aims. We aim to provide an asteroseismic calibration of the wave and convective Rossby numbers, and of the stiffness at the interface between the convective core and radiative envelope of intermediate-mass stars. We deduce these quantities for rotating dwarfs from the observed properties of their identified gravity and gravito-inertial modes. Methods. We relied on near-core rotation rates and asteroseismic models of 26 B- and 37 F-type dwarf pulsators derived from 4-year Kepler space photometry, high-resolution spectroscopy, and Gaia astrometry in the literature to deduce their convective and wave Rossby numbers. We computed the stiffness at the interface of the convective core and the radiative envelope from the inferred maximum buoyancy frequency at the interface and the convective turnover frequency in the core. We use those asteroseismically inferred quantities to make predictions of convective penetration levels, local flux levels of gravito-inertial waves triggered by the convective core, and of the cores’ potential rotational and magnetic states. Results. Our s le of 63 gravito-inertial mode pulsators covers near-core rotation rates from almost zero up to the critical rate. The frequencies of their identified modes lead to models with stiffness values between 10 2.69 and 10 3.60 for the B-type pulsators, while those of F-type stars cover the range from 10 3.47 to 10 4.52 . The convective Rossby numbers derived from the maximum convective diffusion coefficient in the convective core, based on mixing length theory and a value of the mixing length coefficient relevant for these pulsators, vary between 10 −2.3 and 10 −0.8 for B-type stars and 10 −3 and 10 −1.5 for F-type stars. The 17 B-type dwarfs with an asteroseismic estimate of the penetration depth reveal it to be in good agreement with recent theory of convective penetration that takes rotation into account. Theoretical estimates based on the observationally inferred convective Rossby numbers and stiffness values lead to local stochastically-excited gravito-inertial wave fluxes which may exceed those predicted for non-rotating cores, in agreement with observations. Finally, the convective core of rapid rotators is expected to have cylindrical differential rotation causing a magnetic field of 20–400 kG for B-type stars and of 0.1–3 MG for F-type stars. Conclusions. Our results provide asteroseismic calibrations to guide realistic (magneto-)hydrodynamical simultations of rotating (magnetised) core convection in stellar interiors of dwarfs and future modelling of transport and mixing processes in their interiors.
Publisher: EDP Sciences
Date: 05-2020
DOI: 10.1051/0004-6361/202037452
Abstract: Context. Eclipsing, spectroscopic double-lined binary star systems are excellent laboratories for calibrating theories of stellar interior structure and evolution. Their precise and accurate masses and radii measured from binary dynamics offer model-independent constraints and challenge current theories of stellar evolution. Aims. We aim to investigate the mass discrepancy in binary stars. This is the significant difference between stellar components’ masses measured from binary dynamics and those inferred from models of stellar evolution via positions of the components in the T eff − log g Kiel diagram. We study the effect of near-core mixing on the mass of the convective core of the stars and interpret the results in the context of the mass discrepancy. Methods. We fitted stellar isochrones computed from a grid of MESA stellar evolution models to a homogeneous s le of eleven high-mass binary systems. Two scenarios are considered where in idual stellar components of a binary system are treated independent of each other and where they are forced to have the same age and initial chemical composition. We also study the effect of the microturbulent velocity and turbulent pressure on the atmosphere model structure and stellar spectral lines, and its link with the mass discrepancy. Results. We find that the mass discrepancy is present in our s le and that it is anti-correlated with the surface gravity of the star. No correlations are found with other fundamental and atmospheric parameters, including the stellar mass. The mass discrepancy can be partially accounted for by increasing the amount of near-core mixing in stellar evolution models. We also find that ignoring the microturbulent velocity and turbulent pressure in stellar atmosphere models of hot evolved stars results in the overestimation of their effective temperature by up to 8%. Together with enhanced near-core mixing, this can almost entirely account for the ∼30% mass discrepancy found for the evolved primary component of V380 Cyg. Conclusions. We find a strong link between the mass discrepancy and the convective core mass. The mass discrepancy can be solved by considering the combined effect of extra near-core boundary mixing and the consistent treatment in the spectrum analysis of hot evolved stars. Our binary modelling results in convective core masses between 17 and 35% of the stellar mass, which is in excellent agreement with the results from gravity-mode asteroseismology of single stars. This implies larger helium core masses near the end of the main sequence than have been anticipated so far.
Publisher: EDP Sciences
Date: 08-2018
DOI: 10.1051/0004-6361/201832642
Abstract: The large-scale magnetic fields detected at the surface of about 10% of hot stars extend into the stellar interior, where they may alter the structure. Deep inner regions of stars are only observable using asteroseismology. Here, we investigate the pulsating magnetic B3.5V star HD 43317 , infer its interior properties and assess whether the dipolar magnetic field with a surface strength of B p = 1312 ± 332 G causes different properties compared to those of non-magnetic stars. We analyze the latest version of the star’s 150 d CoRoT light curve and extract 35 significant frequencies, 28 of which are found to be independent and not related to the known surface rotation period of P rot = 0.897673 d. We perform forward seismic modeling based on non-magnetic, non-rotating 1D MESA models and the adiabatic module of the pulsation code GYRE, using a grid-based approach. Our aim was to estimate the stellar mass, age, and convective core overshooting. The GYRE calculations were done for uniform rotation with P rot . This modeling is able to explain 16 of the 28 frequencies as gravity modes belonging to retrograde modes with ( ℓ, m ) = (1, −1) and (2, −1) period spacing patterns and one distinct prograde (2, +2) mode. The modeling resulted in a stellar mass M ⋆ = 5.8 −0.2 +0.1 M ⊙ , a central hydrogen mass fraction X c = 0.54 −0.02 +0.01 , and exponential convective core overshooting parameter f ov = 0.004 −0.002 +0.014 . The low value for f ov is compatible with the suppression of near-core mixing due to a magnetic field but the uncertainties are too large to pinpoint such suppression as the sole physical interpretation. We assess the frequency shifts of pulsation modes caused by the Lorentz and the Coriolis forces and find magnetism to have a lower impact than rotation for this star. Including magnetism in future pulsation computations would be highly relevant to exploit current and future photometric time series spanning at least one year, such as those assembled by the Kepler space telescope and expected from the TESS (Continuous Viewing Zone) and PLATO space missions.
Publisher: EDP Sciences
Date: 04-2019
DOI: 10.1051/0004-6361/201834762
Abstract: Context. Space asteroseismology reveals that stellar structure and evolution models of intermediate- and high-mass stars are in need of improvement in terms of angular momentum and chemical element transport. Aims. We aim to probe the interior structure of a hot, massive star in the core-hydrogen-burning phase of its evolution. Methods. We analysed CoRoT space photometry, Gaia DR2 space astrometry, and high-resolution high signal-to-noise HERMES and HARPS time-series spectroscopy of the slowly rotating B2V star HD 170580. Results. From the time-series spectroscopy, we derive v sin i = 4 ± 2 km s −1 , where the uncertainty results from the complex pulsational line-profile variability that has been so far ignored in the literature. We detect 42 frequencies with litudes above five times the local noise level. Amongst these we identify five rotationally split triplets and one quintuplet. Asteroseismic modelling based on CoRoT, Gaia DR2, and spectroscopic data leads to a star of M ∼ 8 M ⊙ near core-hydrogen exhaustion and an extended overshoot zone. The detected low-order pressure-mode frequencies cannot be fit within the uncertainties of the CoRoT data by models without atomic diffusion. Irrespective of this limitation, the low-order gravity modes reveal HD 170580 to be a slow rotator with an average rotation period between 73 and 98 d and a hint of small differential rotation. Conclusions. Future Gaia DR3 data taking into account the multiplicity of the star, along with long-term TESS photometry would allow us to put better observational constraints on the asteroseismic models of this blue evolved massive star. Improved modelling with atomic diffusion, including radiative levitation, is needed to achieve compliance with the low helium surface abundance of the star. This poses immense computational challenges but is required to derive the interior rotation and mixing profiles of this star.
Publisher: Oxford University Press (OUP)
Date: 2020
Abstract: We provide three statistical model prescriptions for the bolometric corrections appropriate for B-type stars as a function of (i) Teff, (ii) Teff and log g, and (iii)Teff, log g and [M/H]. These statistical models have been calculated for 27 different filters, including those of the Gaia space mission, and were derived based on two different grids of bolometric corrections assuming LTE and LTE+NLTE, respectively. Previous such work has mainly been limited to a single photometric passband without taking into account non-local thermodynamic equilibrium (NLTE) effects on the bolometric corrections. Using these statistical models, we calculate the luminosities of 34 slowly pulsating B-type (SPB) stars with available spectroscopic parameters, to place them in the Hertzsprung–Russell diagram and to compare their position to the theoretical SPB instability strip. We find that excluding NLTE effects has no significant effect on the derived luminosities for the temperature range 11 500–21 000 K. We conclude that spectroscopic parameters are needed in order to achieve meaningful luminosities of B-type stars. The three prescriptions for the bolometric corrections are valid for any galactic B-type star with effective temperatures and surface gravities in the ranges 10 000–30 000 K and 2.5–4.5 dex, respectively, covering regimes below the Eddington limit.
Publisher: Frontiers Media SA
Date: 26-02-2020
Publisher: Springer Science and Business Media LLC
Date: 06-05-2019
Publisher: EDP Sciences
Date: 07-2023
DOI: 10.1051/0004-6361/202245650
Abstract: Observations of in idual massive stars, super-luminous supernovae, gamma-ray bursts, and gravitational wave events involving spectacular black hole mergers indicate that the low-metallicity Universe is fundamentally different from our own Galaxy. Many transient phenomena will remain enigmatic until we achieve a firm understanding of the physics and evolution of massive stars at low metallicity ( Z ). The Hubble Space Telescope has devoted 500 orbits to observing ∼250 massive stars at low Z in the ultraviolet (UV) with the COS and STIS spectrographs under the ULLYSES programme. The complementary X-Shooting ULLYSES (XShootU) project provides an enhanced legacy value with high-quality optical and near-infrared spectra obtained with the wide-wavelength coverage X-shooter spectrograph at ESO’s Very Large Telescope. We present an overview of the XShootU project, showing that combining ULLYSES UV and XShootU optical spectra is critical for the uniform determination of stellar parameters such as effective temperature, surface gravity, luminosity, and abundances, as well as wind properties such as mass-loss rates as a function of Z . As uncertainties in stellar and wind parameters percolate into many adjacent areas of astrophysics, the data and modelling of the XShootU project is expected to be a game changer for our physical understanding of massive stars at low Z . To be able to confidently interpret James Webb Space Telescope spectra of the first stellar generations, the in idual spectra of low- Z stars need to be understood, which is exactly where XShootU can deliver.
Publisher: Oxford University Press (OUP)
Date: 19-02-2019
DOI: 10.1093/MNRAS/STZ501
Publisher: American Astronomical Society
Date: 21-01-2014
Publisher: Oxford University Press (OUP)
Date: 04-10-2018
Publisher: American Astronomical Society
Date: 05-2022
Abstract: The chemical evolution of the galaxy is largely guided by the yields from massive stars. Their evolution is heavily influenced by their internal mixing, allowing the stars to live longer and yield a more massive helium core at the end of their main-sequence evolution. Asteroseismology is a powerful tool for studying stellar interiors by providing direct probes of the interior physics of the oscillating stars. This work revisits the recently derived internal mixing profiles of 26 slowly pulsating B stars observed by the Kepler space telescope, in order to investigate how well the mixing profiles can in fact be distinguished from one another as well as provide predictions for the expected helium core masses obtained at the end of the main-sequence evolution. We find that for five of these stars the mixing profile is derived unambiguously, while the remaining stars have at least one other mixing profile which explains the oscillations equally well. Convective penetration is preferred over exponential diffusive overshoot for ≈55% of the stars, while stratified mixing is preferred in the envelope (≈39%). We estimate the expected helium core masses obtained at the end of the main-sequence evolution and find them to be highly influenced by the estimated amount of mixing occurring in the envelopes of the stars.
Publisher: American Astronomical Society
Date: 11-2022
Abstract: One of the largest uncertainties in stellar structure and evolution theory is the transport of angular momentum in the stellar interiors. Asteroseismology offers a powerful tool for measuring the internal rotation frequencies of pulsating stars, but the number of such measurements has remained few for ≳3 M ⊙ main-sequence stars. In this work, we compile a list of 52 slowly pulsating B stars for which the interior rotation has been measured asteroseismically. The measurements of the spin parameters, which describe the relative importance of rotation, for the gravito-inertial mode oscillations show that for 40 of the stars the oscillations fall within the subinertial regime. We find that the core rotation frequencies of the stars decrease as a function of age and show evidence of angular momentum transport occurring on the main sequence. Finally, we derive the inclination angles of the stars, showing that they are generally consistent with the expectations from surface cancellation effects for the given oscillation modes.
Publisher: American Astronomical Society
Date: 15-05-2023
Abstract: Given its large plate scale of 21″ pixel −1 , analyses of data from the Transiting Exoplanet Survey Satellite (TESS) space telescope must be wary of source confusion from blended light curves, which creates the potential to attribute observed photometric variability to the wrong astrophysical source. We explore the impact of light curve contamination on the detection of fast yellow pulsating supergiant (FYPS) stars as a case study to demonstrate the importance of confirming the source of detected signals in the TESS pixel data. While some of the FYPS signals have already been attributed to contamination from nearby eclipsing binaries, others are suggested to be intrinsic to the supergiant stars. In this work, we carry out a detailed analysis of the TESS pixel data to fit the source locations of the dominant signals reported for 17 FYPS stars with the Python package TESS _ localize . We are able to reproduce the detections of these signals for 14 of these sources, obtaining consistent source locations for four. Three of these originate from contaminants, while the signal reported for BZ Tuc is likely a spurious frequency introduced to the light curve of this 127 day Cepheid by the data processing pipeline. Other signals are not significant enough to be localized with our methods, or have long periods that are difficult to analyze given other TESS systematics. Since no localizable signals hold up as intrinsic pulsation frequencies of the supergiant targets, we argue that unambiguous detection of pulsational variability should be obtained before FYPS are considered a new class of pulsator.
Publisher: EDP Sciences
Date: 08-2017
Publisher: Springer Science and Business Media LLC
Date: 10-05-2021
Publisher: EDP Sciences
Date: 2019
DOI: 10.1051/0004-6361/201833662
Abstract: Context. Main sequence stars with a convective core are predicted to stochastically excite internal gravity waves (IGWs), which effectively transport angular momentum throughout the stellar interior and explain the observed near-uniform interior rotation rates of intermediate-mass stars. However, there are few detections of IGWs, and fewer still made using photometry, with more detections needed to constrain numerical simulations. Aims. We aim to formalise the detection and characterisation of IGWs in photometric observations of stars born with convective cores ( M ≳ 1.5 M ⊙ ) and parameterise the low-frequency power excess caused by IGWs. Methods. Using the most recent CoRoT light curves for a s le of O, B, A and F stars, we parameterised the morphology of the flux contribution of IGWs in Fourier space using an MCMC numerical scheme within a Bayesian framework. We compared this to predictions from IGW numerical simulations and investigated how the observed morphology changes as a function of stellar parameters. Results. We demonstrate that a common morphology for the low-frequency power excess is observed in early-type stars observed by CoRoT. Our study shows that a background frequency-dependent source of astrophysical signal is common, which we interpret as IGWs. We provide constraints on the litudes of IGWs and the shape of their detected frequency spectrum across a range of mass, which is the first ensemble study of stochastic variability in such a erse s le of stars. Conclusions. The evidence of a low-frequency power excess across a wide mass range supports the interpretation of IGWs in photometry of O, B, A and F stars. We also discuss the prospects of observing hundreds of massive stars with the Transiting Exoplanet Survey Satellite (TESS) in the near future.
Publisher: American Astronomical Society
Date: 19-07-2018
Publisher: EDP Sciences
Date: 06-2018
DOI: 10.1051/0004-6361/201732317
Abstract: Context. The evolution of stars born with a convective core is highly dependent on the efficiency and extent of near core mixing processes, which effectively increases both the core mass and main-sequence lifetime. These mixing processes remain poorly constrained and therefore result in large uncertainties in the stellar structure and evolution models of such stars. Aims. We investigate to what extent gravity-mode period spacings in slowly pulsating B-type stars observed by the Kepler mission can be used to constrain both the shape and extent of convective core overshoot and additional mixing in the radiative envelope. Methods. We compute grids of 1D stellar structure and evolution models for two different shapes of convective core overshooting and three shapes of radiative envelope mixing. The models in these grids are compared to a set of benchmark models to evaluate their capability of mimicking the dipole prograde g -modes of the benchmark models. Results. Through our model comparisons we find that at a central hydrogen content of X c = 0.5, dipole prograde g -modes in the period range 0.8−3 d are capable of differentiating between step and exponential diffusive overshooting. This ability disappears towards the terminal age main sequence at X c = 0.1. Furthermore, the g -modes behave the same for the three different shapes of radiative envelope mixing considered. However, a constant envelope mixing requires a diffusion coefficient near the convective core five times higher than chemical mixing from internal gravity waves to obtain a surface nitrogen excess of ~ 0.5 dex within the main-sequence lifetime. Conclusions. Within the estimated frequency errors of the Kepler mission, the ability of g -modes to distinguish between step and exponential diffusive overshooting depends on the evolutionary stage. Combining information from the average period spacing and observed surface abundances, notably nitrogen, could potentially be used to constrain the shape of mixing in the radiative envelope of massive stars.
Publisher: Springer Science and Business Media LLC
Date: 06-12-2021
Publisher: EDP Sciences
Date: 08-2019
DOI: 10.1051/0004-6361/201935754
Abstract: Aims. We investigate from a theoretical perspective if space asteroseismology can be used to distinguish between different thermal structures and shapes of the near-core mixing profiles for different types of coherent oscillation modes in massive stars with convective cores we also examine whether this capacity depends on the evolutionary stage of the models along the main sequence. Methods. We computed 1D stellar structure and evolution models for four different prescriptions of the mixing and temperature gradient in the near-core region. We investigated their effect on the frequencies of dipole prograde gravity modes in slowly pulsating B stars and in β Cep stars as well as pressure modes in β Cep stars. Results. A comparison between the mode frequencies of the different models at various stages during the main sequence evolution reveals that they are more sensitive to a change in temperature gradient than to the exact shape of the mixing profile in the near-core region. Depending on the duration of the observed light curve, we can distinguish between either just the temperature gradient, or also between the shapes of the mixing coefficient. The relative frequency differences are in general larger for more evolved models and are largest for the higher frequency pressure modes in β Cep stars. Conclusions. In order to unravel the core boundary mixing and thermal structure of the near-core region, we must have asteroseismic masses and radii with ∼1% relative precision for hundreds of stars.
Publisher: American Astronomical Society
Date: 08-02-2019
Publisher: EDP Sciences
Date: 12-2019
DOI: 10.1051/0004-6361/201936549
Abstract: Context. Extended main-sequence turn-offs (eMSTOs) are a commonly observed property of young clusters. A global theoretical interpretation for eMSTOs is still lacking, but stellar rotation is considered a necessary ingredient to explain eMSTOs. Aims. We aim to assess the importance of core-boundary and envelope mixing in stellar interiors for the interpretation of eMSTOs in terms of one coeval population. Methods. We constructed isochrone-clouds based on interior mixing profiles of stars with a convective core calibrated from asteroseismology of isolated galactic field stars. We fitted these isochrone-clouds to the measured eMSTO to estimate the age and core mass of the stars in the two young clusters NGC 1850 and NGC 884, assuming one coeval population and by fixing the metallicity to the one measured from spectroscopy. We assessed the correlations between the interior mixing properties of the cluster members and their rotational and pulsational properties. Results. We find that stellar models based on asteroseismically-calibrated interior mixing profiles lead to enhanced core masses of eMSTO stars. Additionally, these models can explain a significant fraction of the observed eMSTOs of the two considered clusters in terms of one coeval population of stars, which have similar ages to those in the literature, given the large uncertainties. The rotational and pulsational properties of the stars in NGC 884 are not sufficiently well known to perform asteroseismic modelling as it is achieved for field stars from space photometry. The stars in NGC 884 for which we have v sin i and a few pulsation frequencies show no correlation between these properties and the core masses of the stars that set the cluster age. Conclusions. Future cluster space asteroseismology may allow for the interpretation of the core masses in terms of the physical processes that cause them, based on the modelling of the interior mixing profiles for the in idual member stars with suitable identified modes.
Publisher: MDPI AG
Date: 14-04-2023
Abstract: The convective envelopes of solar-type stars and the convective cores of intermediate- and high-mass stars share boundaries with stable radiative zones. Through a host of processes we collectively refer to as “convective boundary mixing” (CBM), convection can drive efficient mixing in these nominally stable regions. In this review, we discuss the current state of CBM research in the context of main-sequence stars through three lenses. (1) We examine the most frequently implemented 1D prescriptions of CBM—exponential overshoot, step overshoot, and convective penetration—and we include a discussion of implementation degeneracies and how to convert between various prescriptions. (2) Next, we examine the literature of CBM from a fluid dynamical perspective, with a focus on three distinct processes: convective overshoot, entrainment, and convective penetration. (3) Finally, we discuss observational inferences regarding how much mixing should occur in the cores of intermediate- and high-mass stars as well as the implied constraints that these observations place on 1D CBM implementations. We conclude with a discussion of pathways forward for future studies to place better constraints on this difficult challenge in stellar evolution modeling.
Publisher: Springer Science and Business Media LLC
Date: 26-05-2021
Publisher: American Astronomical Society
Date: 26-04-2019
Location: China
Location: United States of America
No related grants have been discovered for May Gade Pedersen.