The sun and asteroseismology

Introduction

The Sun is the best laboratory for stellar physics. The properties of the solar interior are known with great detail. This is possible because the Sun oscillates in hundreds of thousands of acoustic modes (p-modes) and the frequencies are measured to very high precision (typically, one part in 105) both from space-born missions and Earth-based solar observatories. The study of these oscillations, helioseismology, allows inferring the inner structure of the Sun -i.e. the run of density, temperature, pressure and even rotation with radius- very accurately and precisely. Measurements of solar neutrino fluxes, especially by the SNO, SuperK and Borexino experiments, give complementary constraints on the innermost solar core. Due to the extremely high sensitivity of neutrino production on the solar core temperature, solar neutrinos are an excellent thermometer (better than 1%) of the solar interior.

Due to this wealth of data our understanding of stellar structure and evolution can be subject to stringent tests when trying to reproduce solar properties. The Sun is a fundamental benchmark against which modeling of physical processes in stars is tested. Non-standard processes in stellar evolution such as mechanisms of angular momentum transport, chemical mixing due to dynamical instabilities, the effect of dark matter candidate particles in stellar evolution can be tested in solar models, where even small effects in the resulting solar properties can be tested against observations.
 
Solar models have been very successful in the past. So much, that even in the late 1990s the agreement between solar model predictions and helioseismic inferences of the solar interior ruled out an astrophysical solution to the solar neutrino problem and gave a very strong support to the idea of neutrino oscillations, several years before Kamiokande and SNO discovered them. But in the past decade, a new challenge has emerged. The development of 3D simulations of the solar atmosphere and more refined spectroscopic analysis tools have led to predictions about the solar composition that, when coupled with solar models, lead to strong disagreements with helioseismic and solar neutrino results. The “solar abundance problem” is then a conflict between state-of-the-art solar (stellar) interior models and solar (stellar) atmosphere models and spectroscopic analysis. Its solution has now defied more than 10 years of continuous attempts including, among others: solar models with exotic energy transport and/or energy losses, dynamical effects in solar interiors (rotation, angular and energy transport by gravity waves). The “solar abundance problem” highlights the limitations in our understanding of stellar physics in general, and so its implications have far reaching consequences affecting every branch in astrophysics where stellar modeling matters.
 
The advent of space-borne asteroseismology, initially with the Corot and Kepler missions, now with K2 and TESS and PLATO in the near and mid-term, has open up a new window to studies of stellar interiors. Stellar oscillations give us a unique way of piercing the surface of stars and learn about their internal structure. Asteroseismic studies, particularly of solar-like oscillators such as cool main sequence and red giant branch stars, allow in combination with state-of-the-art stellar models the characterization of fundamental stellar properties such as their mass, radius and very importantly age.

With its rapid development, asteroseismology has become, in less than a decade, a fundamental tool not only in studies of stellar physics, but also in the study of exoplanet hosting stars and systems, and galactic archaeology.

Focus

The fundamental and unifying line of work is the theoretical studies of the solar and stellar interiors by means of state-of-the-art structure and evolution models.

Our ultimate goal is to develop and test the most accurate solar and stellar models, and then using these models to address several scientific issues. The development of models is carried out along several paths: improvement of the microphysics used in the models (nuclear reation rates, opacities, equation of state), better modeling of physical processes (e.g. near-surface convection based on 3D hydrodynamic models) and numerical techniques. Models are tested several different constraints from helioseismology to eclipsing binaries to asteroseismology, also complemented with parallaxes from Gaia.
 
Some of the scientific problems we are interested in addressing are: the solar abundance problem, solar models for particle physics including work on solar neutrinos, and constraints on exotic properties of matter (e.g. magnetic neutrino dipole) and/or properties of exotic matter (e.g. dark matter candidates). Also, we are interested in any application of stellar models to astrophysical problems. Based on spectroscopic, photometric, asteroseismic and astrometric data (any combination thereof) we work on the characterization of stellar properties that enable studies from individual objects (such as planet hosting stars) or large-scale populations. For attacking some of these topics, we have also developed BeSPP (Bellaterra Stellar Parameters Pipeline), a state-of-the-art statistical analysis tool based on Bayesian statistics that allow inference of stellar parameters based on different classes of input data and a large library of stellar models containing about 100 millon models.
 
We are part of the Gaia-ESO survey, the Kepler and K2 mission, and are external collaborators in APOGEE, the SDSS-IV experiment for galactic archaeology. We are also members of the Steering Committee of the working group of solar like oscillators of the oncoming NASA mission TESS.
Selected publications

A new generation of standard solar models
Vinyoles, N., Serenelli, A., et al.
The Astrphysical Journal, Volume 835, article id. 202, 2017
 
Measuring the vertical age structure of the Galactic disc using
asteroseismology and SAGA
Casagrande, L., Silve Aguirre, V., et al. (Serenelli co-I of SAGA)
Monthly Notices of the Royal Astronomical Society, Volume 455, p.987-1007, 2016
 
The Gaia-ESO Survey: Hydrogen lines in red giants directly trace stellar mass
Bergemann, M., Serenelli, A. and the Gaia-ESO collaboration
Astronomy & Astrophysics, Voume 594, article id. A120, 2016
 
Possible Indication of Momentum-Dependent Asymmetric Dark Matter in the Sun
Vincent, A., Scott, P., Serenelli, A.
Physical Review Letters, Volume 114, id.081302, 2015
 
Bayesian analysis of ages, masses and distances to cool stars with non-LTE spectroscopic parameters
Serenelli, A., Bergemann, M., Ruchti G., Casagrande L.
Monthly Notices of the Royal Astronomical Society, Volume 429, p.3645-3657, 2013
 
Multi-periodic pulsations of a stripped red-giant star in an eclipsing binary system
Maxted, P., Serenelli, A., et al.
Nature, Volume 498, pp-463-465, 2013

Senior Institute members involved

A. Serenelli
Institute of Space Sciences (IEEC-CSIC)

Campus UAB, Carrer de Can Magrans, s/n
08193 Barcelona.
Phone: +34 93 737 9788
Email: ice@ice.csic.es
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An institute of the Consejo Superior de Investigaciones Científicas

An institute of the Consejo Superior de Investigaciones Científicas
Affiliated with the Institut d'Estudis Espacials de Catalunya

Affiliated with the Institut d'Estudis Espacials de Catalunya