CORDIS - EU research results

Sounding Stars with Kepler

Final Report Summary - ASK (Sounding Stars with Kepler)

The Project ASK aimed at exploring aspects of stellar modelling and interpretation of the asteroseismic data by high precision asteroseismology performed for a large sample of stars in various evolutionary stage. We took advantage of the fact that stellar oscillations are the only diagnostic known today that can reach the required precision of derivation the interior and global properties of stars. We focused on solar-type stars which show solar-like oscillations and the classical pulsators but we analyzed also pulsating stars of other types.

The observations analyzed in the framework of the Project ASK were obtained with the space telescope Kepler and its continuation, the K2 mission, and with the ground-based instruments. The ground-based follow-up observations of Kepler asteroseismic targets were carried out at the Mauna Kea Observatory (Hawaii, USA), the Kitt Peak Observatory (Arizona, USA), the Apache Point Observatory (New Mexico, USA), and the Observatorio del Roque de los Muchachos (ORM, Spain). Additional data were acquired with the help of American Association of Variable Star Observers (AAVSO) and the Microvariability and Oscillations of STars telescope (MOST).

The unprecedented quality of the Kepler and K2 observations, complemented with ground-based follow-up spectroscopic, photometric and interferometric observations, allowed not only for a determination of the fundamental parameters of the stars, such as metallicity, rotation, and compositional gradients, but also a for high-precision seismic description of the interiors of individual stars. During the 56 months of the Project ASK we reached our aim of ensuring a complete and exhaustive exploitation of the Kepler and K2 data. We accelerated and facilitated the process of deriving information about the Kepler and K2 targets and providing information crucial for the studies of the planetary systems discovered in the Kepler and K2 missions. Those goals were reached by reducing uncertainties of asteroseismic models related to the interior constitutive physics, which include processes such as turbulence, differential rotation, and other 3-D effects, and various shortcomings of current nonlinear pulsation theory in describing mode coupling, excitation, and damping.

To ensure an efficient analysis of the ground-based and satellite data, we constructed dedicated pipelines that allowed automatic data calibration, reduction, and analysis. Among them there is the code Asymptotic Analysis of Red Giants (AARG) that allows for deriving asymptotic parameters for p-modes and observed period spacings for mixed modes in red giants, the high-DImensional And multi-MOdal NesteD Sampling code (DIAMONDS) that can be used for any application involving Bayesian parameter estimation and/or model selection problems, the Asteroseismic Modeling Portal (AMP) that provides scientists and easy access to the software and computational resources required for asteroseismology, and several tools which facilitate the analysis of the data produced by the Kepler and K2 missions and which are available at the web site of the Kepler Asteroseismic Science Operations Center (KASOC) that provides asteroseismological data from the NASA Kepler mission to astronomers who are members of the Kepler Asteroseismic Science Consortium (KASC).

The total number of publications resulting from the Project ASK exceeded 100.

In the framework of the Project ASK, we provided asteroseismic models of various types of stars being at different stages of the stellar life and in a wide range of stellar masses with the purpose to connect the stellar structure models with each other to reconstruct the stellar evolution. The confrontation between the measured frequencies and those predicted by models allowed us to pinpoint some of the limitations of the assumed physics of the stellar interiors and guided us towards the ways to improve the understanding of the physics of stellar interiors. We set the constraints on the relationship between the mode of oscillation linewidth at maximum oscillation amplitude and the effective temperature of the star, we characterized the surface rotation and the properties of the p-mode parameters of solar-like stars, and we investigated the equidistant period spacings in gamma Doradus stars providing also their asteroseismic models. Our asteroseismic analysis allowed us to derive very precise radii of the studied stars. By applying seismic techniques to such a broad range of stellar types, we achieved a vast increase in the range of physical circumstances over which the physics of stellar interiors can be probed. This innovative application of the classic asteroseismic methods of the data analysis resulted in the first, so vast, detailed and thorough study of solar-like stars and their planets. For a few, brightest Kepler targets, our results were confirmed by the analysis of interferometric observations.

The number of the scientists exchanged in the Project ASK, i.e. those who traveled between the European institutes, which included the Uniwersytet Wroclawski (Poland), the Aarhus Universitet (Denmark), the Centro de Investigacao em Astronomia e Astrofisica da Universidade do Porto (Portugal), the Commissariat a l'energie atomique et aux energies alternatives (France), the Instituto de Astrofísica de Canarias (Spain), the Istituto Nazionale di Astrofisica (Italy), and the Magyar Tudomanyos Akademia Csillagaszati Es Foldtudomanyi Kutatokozpont (Hungary), and the Third Country institutes, which included the Smithsonian Institution (USA), the Los Alamos National Security LLC (USA), The University Corporation for Atmospheric Research (USA), The Regents of New Mexico State University (USA), the Yale University (USA) and the University of Sydney (Australia), was 53 (19 women and 34 men), however, the number of scientists who were indirectly involved in the realization of this Project was significantly higher.

The results of our work have been presented at different international conferences and at seminars held at Partner Institutes, and the Project was promoted at various meetings and exhibitions. That intense cooperation strengthened the bonds between the participating Institutes, facilitated the exchange of knowledge, helped the young researchers continue their scientific career, and enriched the scientific interests of the experienced staff.

The results of the Project ASK will affect also other fields that stand for the state-of-the-art of the modern astrophysical research because many studies within the modern astrophysics rely on stellar structure and evolution models.