Filter and export

Publications

What is a Publication?
23 Publications visible to you, out of a total of 23
APOKASC-3: The Third Joint Spectroscopic and Asteroseismic Catalog for Evolved Stars in the Kepler Fields

Abstract (Expand)

In the third APOKASC catalog, we present data for the complete sample of 15,808 evolved stars with APOGEE spectroscopic parameters and Kepler asteroseismology. We used 10 independent asteroseismic … analysis techniques and anchor our system on fundamental radii derived from Gaia L and spectroscopic Teff. We provide evolutionary state, asteroseismic surface gravity, mass, radius, age, and the data used to derive them for 12,418 stars. This includes 10,036 exceptionally precise measurements, with median fractional uncertainties in ν max, Δ ν, mass, radius, and age of 0.6%, 0.6%, 3.8%, 1.8%, and 11.1%, respectively. We provide more limited data for 1624 additional stars that either have lower-quality data or are outside of our primary calibration domain. Using lower red giant branch (RGB) stars, we find a median age for the chemical thick disk of 9.14 ± 0.05(ran) ± 0.9(sys) Gyr with an age dispersion of 1.1 Gyr, consistent with our error model. We calibrate our red clump (RC) mass loss to derive an age consistent with the lower RGB and provide asymptotic GB and RGB ages for luminous stars. We also find a sharp upper-age boundary in the chemical thin disk. We find that scaling relations are precise and accurate on the lower RGB and RC, but they become more model dependent for more luminous giants and break down at the tip of the RGB. We recommend the use of multiple methods, calibration to a fundamental scale, and the use of stellar models to interpret frequency spacings.

Authors: Marc H. Pinsonneault, Joel C. Zinn, Jamie Tayar, Aldo Serenelli, Rafael A. García, Savita Mathur, Mathieu Vrard, Yvonne P. Elsworth, Benoit Mosser, Dennis Stello, Keaton J. Bell, Lisa Bugnet, Enrico Corsaro, Patrick Gaulme, Saskia Hekker, Marc Hon, Daniel Huber, Thomas Kallinger, Kaili Cao, Jennifer A. Johnson, Bastien Liagre, Rachel A. Patton, Ângela R. G. Santos, Sarbani Basu, Paul G. Beck, Timothy C. Beers, William J. Chaplin, Katia Cunha, Peter M. Frinchaboy, Léo Girardi, Diego Godoy-Rivera, Jon A. Holtzman, Henrik Jönsson, Szabolcs Mészáros, Claudia Reyes, Hans-Walter Rix, Matthew Shetrone, Verne V. Smith, Taylor Spoo, Keivan G. Stassun, Ji Wang

Date Published: 5th Feb 2025

Publication Type: Journal

The robustness of inferred envelope and core rotation rates of red giant stars from asteroseismology

Abstract (Expand)

Context. Rotation is an important phenomenon influencing stellar structure and evolution, however, it has not been adequately modelled thus far. Therefore, accurate estimates of internal rotation rates … are valuable for constraining stellar evolution models. Aims. We aim to assess the accuracy of asteroseismic estimates of internal rotation rates and how they depend on the fundamental stellar parameters. Methods. We applied the recently developed extended-multiplicative optimally localised averages (eMOLA) inversion method, to infer localised estimates of internal rotation rates of synthetic observations of red giants. We searched for suitable reference stellar models, following a grid-based approach, and we assessed the robustness of the resulting inferences with respect to the choice of reference model. Results. We find that matching the mixed-mode pattern between the observation and the reference model is an important criterion for selecting suitable reference models. We propose (i) selecting a set of reference models based on the correlation between the observed rotational splittings and the mode-trapping parameter; (ii) computing the rotation rates for all these models; and (iii) using the average value obtained across the whole set as the estimate of the internal rotation rates. We find that the effect of a near surface perturbation in the synthetic observations on the rotation rates estimated based on the correlation between the observed rotational splittings and the mode-trapping parameter is negligible. Conclusions. We conclude that when using an ensemble of reference models that are selected by matching the mixed-mode pattern, the input rotation rates can be recovered across a range of fundamental stellar parameters such as mass, mixing-length parameter, and composition. Further, red giant rotation rates determined in this way are also independent of any near-surface perturbation of the stellar structure.

Authors: F. Ahlborn, E. P. Bellinger, S. Hekker, S. Basu, D. Mokrytska

Date Published: 2025

Publication Type: Journal

Merger seismology: Distinguishing massive merger products from genuine single stars using asteroseismology

Abstract (Expand)

Products of stellar mergers are predicted to be common in stellar populations and can potentially explain stars with peculiar properties. When the merger occurs after the initially more massive star …ar has evolved into the Hertzsprung gap, the merger product may remain in the blue part of the Hertzsprung–Russell diagram for millions of years. Such objects could, therefore, explain the overabundance of observed blue stars, such as blue supergiants. However, it is currently not straightforward to distinguish merger products from genuine single stars or other stars with similar surface diagnostics. In this work, we made detailed asteroseismic comparisons between models of massive post-main-sequence merger products and genuine single stars to identify which asteroseismic diagnostics can be used to distinguish them. In doing so, we developed tools for the relatively young field of merger seismology. Genuine single stars in the Hertzsprung gap are fully radiative, while merger products have a convective He-burning core and convective H-burning shell while occupying similar locations in the Hertzsprung–Russell diagram. These major structural differences are reflected in lower asymptotic period spacing values for merger products and the appearance of deep dips in their period spacing patterns. Our genuine single-star models with masses above roughly 11.4 solar masses develop short-lived intermediate convective zones during their Hertzsprung gap evolution. This also leads to deep dips in their period spacing patterns. Because of the lack of a convective core, merger products and genuine single stars can be distinguished based on their asymptotic period spacing value in this mass range. We performed the comparisons with and without the effects of slow rotation included in the pulsation equations and conclude that the two types of stars are seismically distinguishable in both cases. The observability of the distinguishing asteroseismic features of merger products can now be assessed and exploited in practice.

Authors: J. Henneco, F. R. N. Schneider, S. Hekker, C. Aerts

Date Published: 1st Oct 2024

Publication Type: Journal

Merger seismology: Distinguishing massive merger products from genuine single stars using asteroseismology

Abstract (Expand)

Products of stellar mergers are predicted to be common in stellar populations and can potentially explain stars with peculiar properties. When the merger occurs after the initially more massive star … has evolved into the Hertzsprung gap, the merger product may remain in the blue part of the Hertzsprung–Russell diagram for millions of years. Such objects could, therefore, explain the overabundance of observed blue stars, such as blue supergiants. However, it is currently not straightforward to distinguish merger products from genuine single stars or other stars with similar surface diagnostics. In this work, we made detailed asteroseismic comparisons between models of massive post-main-sequence merger products and genuine single stars to identify which asteroseismic diagnostics can be used to distinguish them. In doing so, we developed tools for the relatively young field of merger seismology. Genuine single stars in the Hertzsprung gap are fully radiative, while merger products have a convective He-burning core and convective H-burning shell while occupying similar locations in the Hertzsprung–Russell diagram. These major structural differences are reflected in lower asymptotic period spacing values for merger products and the appearance of deep dips in their period spacing patterns. Our genuine single-star models with masses above roughly 11.4 solar masses develop short-lived intermediate convective zones during their Hertzsprung gap evolution. This also leads to deep dips in their period spacing patterns. Because of the lack of a convective core, merger products and genuine single stars can be distinguished based on their asymptotic period spacing value in this mass range. We performed the comparisons with and without the effects of slow rotation included in the pulsation equations and conclude that the two types of stars are seismically distinguishable in both cases. The observability of the distinguishing asteroseismic features of merger products can now be assessed and exploited in practice.

Authors: J. Henneco, F. R. N. Schneider, S. Hekker, C. Aerts

Date Published: 1st Oct 2024

Publication Type: Journal

The radial modes of stars with suppressed dipole modes

Abstract (Expand)

Context. The Kepler space mission provided high-quality light curves for more than 16 000 red giants. The global stellar oscillations extracted from these light curves carry information about the … interior of the stars. Several hundred red giants were found to have low amplitudes in their dipole modes (i.e. they are suppressed dipole-mode stars). A number of hypotheses (involving e.g. a magnetic field, binarity, or resonant mode coupling) have been proposed to explain the suppression of the modes, yet none has been confirmed. Aims. We aim to gain insight into the mechanism at play in suppressed dipole-mode stars by investigating the mode properties (linewidths, heights, and amplitudes) of the radial oscillation modes of red giants with suppressed dipole modes. Methods.We selected from the literature suppressed dipole-mode stars and compared the radial-mode properties of these stars to the radial-mode properties of stars in two control samples of stars with typical (i.e. non-suppressed) dipole modes. Results. We find that the radial-mode properties of the suppressed dipole-mode stars are consistent with the ones in our control samples, and hence not affected by the suppression mechanism. Conclusions. From this we conclude that (1) the balance between the excitation and damping in radial modes is unaffected by the suppression, and by extrapolation the excitation of the non-radial modes is not affected either; and (2) the damping of the radial modes induced by the suppression mechanism is significantly less than the damping from turbulent convective motion, suggesting that the additional damping originates from the more central non-convective regions of the star, to which the radial modes are least sensitive.

Authors: Q. Coppée, J. Müller, M. Bazot, S. Hekker

Date Published: 1st Oct 2024

Publication Type: Journal

Merger seismology: Asteroseismic properties of massive merger products

Abstract

Not specified

Authors: Jan Henneco, Fabian R. N. Schneider, Saskia Hekker, Conny Aerts

Date Published: 1st Sep 2024

Publication Type: InProceedings

The K2 Asteroseismic KEYSTONE sample of Dwarf and Subgiant Solar-Like Oscillators

Abstract (Expand)

Aims. The KEYSTONE project aims to enhance our understanding of solar-like oscillators by delivering a catalogue of global asteroseismic parameters (Δv and v max) for 173 stars, comprising mainly dwarfs … and subgiants, observed by the K2 mission in its short-cadence mode during campaigns 6–19. Methods. We derive atmospheric parameters and luminosities using spectroscopic data from TRES, astrometric data from Gaia, and the infrared flux method (IRFM) for a comprehensive stellar characterisation. Asteroseismic parameters are robustly extracted using three independent methods, complemented by an iterative refinement of the spectroscopic analyses using seismic log g values to enhance parameter accuracy. Results. Our analysis identifies new detections of solar-like oscillations in 159 stars, providing an important complement to already published results from previous campaigns. The catalogue provides homogeneously derived atmospheric parameters and luminosities for the majority of the sample. Comparison between spectroscopic Teff and those obtained from the IRFM demonstrates excellent agreement. The iterative approach to spectroscopic analysis significantly enhances the accuracy of the stellar properties derived.

Authors: Mikkel N. Lund, Sarbani Basu, Allyson Bieryla, Luca Casagrande, Daniel Huber, Saskia Hekker, Lucas Viani, Guy R. Davies, Tiago L. Campante, William J. Chaplin, Aldo M. Serenelli, J. M. Joel Ong, Warrick H. Ball, Amalie Stokholm, Earl P. Bellinger, Michaël Bazot, Dennis Stello, David W. Latham, Timothy R. White, Maryum Sayeed, Víctor Aguirre Børsen-Koch, Ashley Chontos

Date Published: 1st Aug 2024

Publication Type: Journal

Powered by
 (v.1.16.0)
About HITS Publication SEEK | About HITS-Publication-SEEK | Funding and Programmes | Credits
Copyright © 2008 - 2024 The University of Manchester and HITS gGmbH