Convective boundary mixing in low- and intermediate-mass stars – I. Core properties from pressure-mode asteroseismology

ABSTRACT Convective boundary mixing (CBM) is ubiquitous in stellar evolution. It is a necessary ingredient in the models in order to match observational constraints from clusters, binaries, and single stars alike. We compute ‘effective overshoot’ measures that reflect the extent of mixing and which can differ significantly from the input overshoot values set in the stellar evolution codes. We use constraints from pressure modes to infer the CBM properties of Kepler and CoRoT main-sequence and subgiant oscillators, as well as in two radial velocity targets (Procyon A and α Cen A). Collectively, these targets allow us to identify how measurement precision, stellar spectral type, and overshoot implementation impact the asteroseismic solution. With these new measures, we find that the ‘effective overshoot’ for most stars is in line with physical expectations and calibrations from binaries and clusters. However, two F-stars in the CoRoT field (HD 49933 and HD 181906) still necessitate high overshoot in the models. Due to short mode lifetimes, mode identification can be difficult in these stars. We demonstrate that an incongruence between the radial and non-radial modes drives the asteroseismic solution to extreme structures with highly efficient CBM as an inevitable outcome. Understanding the cause of seemingly anomalous physics for such stars is vital for inferring accurate stellar parameters from TESS data with comparable timeseries length.

Download Full-text

Rotating and magnetic stellar models of intermediate-mass stars up to the AGB

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318006051 ◽

2018 ◽

Vol 14 (S343) ◽

pp. 468-469

Author(s):

Luiz T. S. Mendes ◽

Natália R. Landin ◽

Paolo Ventura

Keyword(s):

Magnetic Field ◽

Stellar Evolution ◽

Large Scale ◽

Main Sequence ◽

Agb Stars ◽

Intermediate Mass ◽

Intermediate Mass Stars ◽

Large Scale Magnetic Field ◽

Stellar Models ◽

Effects Of Rotation

AbstractAiming at investigating the roles of rotation and magnetic fields on AGB stars, the rotating version of the ATON stellar evolution code is being extended in order to account for intermediate--mass stars and their later evolutionary stages. Here we report some preliminary results on the effects of rotation and of a large-scale magnetic field on the structure and evolution of 3 and 5 M⊙ stellar models from the pre-main sequence up to the AGB.

Download Full-text

Progenitors of Core-Collapse Supernovae

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317004896 ◽

2017 ◽

Vol 12 (S331) ◽

pp. 1-10

Author(s):

R. Hirschi ◽

D. Arnett ◽

A. Cristini ◽

C. Georgy ◽

C. Meakin ◽

...

Keyword(s):

Stellar Evolution ◽

Massive Stars ◽

Core Collapse ◽

Strong Impact ◽

Convective Boundary ◽

Hydrodynamic Simulations ◽

Boundary Mixing ◽

Intermediate Mass Stars ◽

Key Points ◽

Carbon Burning

AbstractMassive stars have a strong impact on their surroundings, in particular when they produce a core-collapse supernova at the end of their evolution. In these proceedings, we review the general evolution of massive stars and their properties at collapse as well as the transition between massive and intermediate-mass stars. We also summarise the effects of metallicity and rotation. We then discuss some of the major uncertainties in the modelling of massive stars, with a particular emphasis on the treatment of convection in 1D stellar evolution codes. Finally, we present new 3D hydrodynamic simulations of convection in carbon burning and list key points to take from 3D hydrodynamic studies for the development of new prescriptions for convective boundary mixing in 1D stellar evolution codes.

Download Full-text

Stellar Mass Loss and Pulsation

International Astronomical Union Colloquium ◽

10.1017/s0252921100011453 ◽

1989 ◽

Vol 111 ◽

pp. 63-82

Author(s):

L.A. Willson

Keyword(s):

Mass Loss ◽

Stellar Evolution ◽

Effective Temperature ◽

Large Amplitude ◽

Main Sequence ◽

Massive Stars ◽

Sequence Evolution ◽

Intermediate Mass ◽

Mira Variables ◽

Intermediate Mass Stars

AbstractMass loss at rates sufficient to alter the evolution of stars is known to occur during the pre-main sequence evolution of most stars, on the main sequence for massive stars, and during advanced evolutionary phases when the luminosity is high and the effective temperature is low. While most investigations of the effects of mass loss on stellar evolution have assumed continuous (parametrized) mass loss laws apply, there is increasing evidence that mass loss rates are substantially higher for stars that are pulsating with large amplitude and/or in selected modes. Some new insights into the mass loss that terminates the AGB evolution of intermediate mass stars, and leads to the formation of planetary nebulae, come from recent detailed studies of the mass loss process from the Mira variables.

Download Full-text

AGB Winds with Gas-Dust Drift in Stellar Evolution Codes

Universe ◽

10.3390/universe7050113 ◽

2021 ◽

Vol 7 (5) ◽

pp. 113

Author(s):

Lars Mattsson ◽

Christer Sandin

Keyword(s):

Stellar Evolution ◽

Loss Rate ◽

Mass Loss Rate ◽

Carbon Star ◽

Intermediate Mass ◽

Future Directions ◽

Physical Description ◽

Intermediate Mass Stars ◽

Dust Component ◽

Improved Model

A significant fraction of new metals produced in stars enter the interstellar medium in the form of dust grains. Including dust and wind formation in stellar evolution models of late-stage low- and intermediate-mass stars provides a way to quantify their contribution to the cosmic dust component. In doing so, a correct physical description of dust formation is of course required, but also a reliable prescription for the mass-loss rate. Here, we present an improved model of dust-driven winds to be used in stellar evolution codes and insights from recent detailed numerical simulations of carbon-star winds including drift (decoupling of dust and gas). We also discuss future directions for further improvement.

Download Full-text

IPHAS A-type Stars with Mid-IR Excesses in Spitzer Surveys

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310011932 ◽

2009 ◽

Vol 5 (H15) ◽

pp. 815-815

Author(s):

Antonio S. Hales ◽

Michael J. Barlow ◽

Janet E. Drew ◽

Yvonne C. Unruh ◽

Robert Greimel ◽

...

Keyword(s):

Cross Correlation ◽

Main Sequence ◽

Terrestrial Planet ◽

Circumstellar Disks ◽

Main Sequence Stars ◽

Intermediate Mass ◽

Mid Infrared ◽

Isaac Newton ◽

Intermediate Mass Stars ◽

Dust Disks

AbstractThe Isaac Newton Photometric H-Alpha Survey (IPHAS) provides (r′-Hα)-(r′-i′) colors, which can be used to select AV0-5 Main Sequence star candidates (age~20-200 Myr). By combining a sample of 23050 IPHAS-selected A-type stars with 2MASS, GLIMPSE and MIPSGAL photometry we searched for mid-infrared excesses attributable to dusty circumstellar disks. Positional cross-correlation yielded a sample of 2692 A-type stars, of which 0.6% were found to have 8-μm excesses above the expected photospheric values. The low fraction of main sequence stars with mid-IR excesses found in this work indicates that dust disks in the terrestrial planet zone of Main Sequence intermediate mass stars are rare. Dissipation mechanisms such as photo-evaporation, grain growth, collisional grinding or planet formation could possibly explain the depletion of dust detected in the inner regions of these disks.

Download Full-text

Small and Intermediate Mass Stellar Evolution - Main Sequence and Close to It

International Astronomical Union Colloquium ◽

10.1017/s0252921100018169 ◽

1993 ◽

Vol 137 ◽

pp. 410-425 ◽

Cited By ~ 1

Author(s):

A. Noels ◽

N. Grevesse

Keyword(s):

Mass Loss ◽

Stellar Evolution ◽

Turbulent Diffusion ◽

Main Sequence ◽

Main Sequence Stars ◽

Intermediate Mass ◽

Physical Mechanisms ◽

Standard Models

AbstractWe present the standard models for small and intermediate main sequence stars and we discuss some of the problems arising with semiconvection and overshooting. The surface abundance of Li serves as a test for other physical mechanisms, including microscopic and turbulent diffusion, rotation and mass loss.

Download Full-text

The effects of Rotation on Wolf–Rayet Stars and on the Production of Primary Nitrogen by Intermediate Mass Stars

Symposium - International Astronomical Union ◽

10.1017/s007418090019624x ◽

2004 ◽

Vol 215 ◽

pp. 579-588 ◽

Cited By ~ 2

Author(s):

Georges Meynet ◽

Max Pettini

Keyword(s):

Star Formation ◽

Time Delay ◽

Main Sequence ◽

Massive Stars ◽

Sequence Evolution ◽

Stellar Rotation ◽

Intermediate Mass ◽

Intermediate Mass Stars ◽

Solar Metallicity ◽

Effects Of Rotation

We use the rotating stellar models described in the paper by A. Maeder & G. Meynet in this volume to consider the effects of rotation on the evolution of the most massive stars into and during the Wolf–Rayet phase, and on the post-Main Sequence evolution of intermediate mass stars. The two main results of this discussion are the following. First, we show that rotating models are able to account for the observed properties of the Wolf–Rayet stellar populations at solar metallicity. Second, at low metallicities, the inclusion of stellar rotation in the calculation of chemical yields can lead to a longer time delay between the release of oxygen and nitrogen into the interstellar medium following an episode of star formation, since stars of lower masses (compared to non-rotating models) can synthesize primary N. Qualitatively, such an effect may be required to explain the relative abundances of N and O in extragalactic metal–poor environments, particularly at high redshifts.

Download Full-text

The Pan-Pacific Planet Search – VIII. Complete results and the occurrence rate of planets around low-luminosity giants

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3378 ◽

2019 ◽

Vol 491 (4) ◽

pp. 5248-5257 ◽

Cited By ~ 3

Author(s):

Robert A Wittenmyer ◽

R P Butler ◽

Jonathan Horner ◽

Jake Clark ◽

C G Tinney ◽

...

Keyword(s):

Radial Velocity ◽

Main Sequence ◽

Giant Planets ◽

Occurrence Rate ◽

Velocity Measurements ◽

Intermediate Mass ◽

Giant Stars ◽

Intermediate Mass Stars ◽

Final Data ◽

Solar Type

ABSTRACT Our knowledge of the populations and occurrence rates of planets orbiting evolved intermediate-mass stars lags behind that for solar-type stars by at least a decade. Some radial velocity surveys have targeted these low-luminosity giant stars, providing some insights into the properties of their planetary systems. Here, we present the final data release of the Pan-Pacific Planet Search (PPPS), a 5 yr radial velocity survey using the 3.9 m Anglo-Australian Telescope. We present 1293 precise radial velocity measurements for 129 stars, and highlight 6 potential substellar-mass companions, which require additional observations to confirm. Correcting for the substantial incompleteness in the sample, we estimate the occurrence rate of giant planets orbiting low-luminosity giant stars to be approximately 7.8$^{+9.1}_{-3.3}$ per cent. This result is consistent with the frequency of such planets found to orbit main-sequence A-type stars, from which the PPPS stars have evolved.

Download Full-text