Ages and fundamental properties of Kepler exoplanet host stars from asteroseismology (1504.07992v2)

Abstract: We present a study of 33 {\it Kepler} planet-candidate host stars for which asteroseismic observations have sufficiently high signal-to-noise ratio to allow extraction of individual pulsation frequencies. We implement a new Bayesian scheme that is flexible in its input to process individual oscillation frequencies, combinations of them, and average asteroseismic parameters, and derive robust fundamental properties for these targets. Applying this scheme to grids of evolutionary models yields stellar properties with median statistical uncertainties of 1.2\% (radius), 1.7\% (density), 3.3\% (mass), 4.4\% (distance), and 14\% (age), making this the exoplanet host-star sample with the most precise and uniformly determined fundamental parameters to date. We assess the systematics from changes in the solar abundances and mixing-length parameter, showing that they are smaller than the statistical errors. We also determine the stellar properties with three other fitting algorithms and explore the systematics arising from using different evolution and pulsation codes, resulting in 1\% in density and radius, and 2\% and 7\% in mass and age, respectively. We confirm previous findings of the initial helium abundance being a source of systematics comparable to our statistical uncertainties, and discuss future prospects for constraining this parameter by combining asteroseismology and data from space missions. Finally we compare our derived properties with those obtained using the global average asteroseismic observables along with effective temperature and metallicity, finding an excellent level of agreement. Owing to selection effects, our results show that the majority of the high signal-to-noise ratio asteroseismic {\it Kepler} host stars are older than the Sun.

• The paper introduces a Bayesian method combining individual oscillation frequencies and global parameters to determine stellar ages with high precision.
• It achieves median uncertainties of 1.2% for radius, 1.7% for density, 3.3% for mass, and 14% for age, ensuring robust stellar property measurements.
• Results validate scaling relations while highlighting the effects of microscopic diffusion and convective overshooting on derived stellar ages.

Overview of "Ages and Fundamental Properties of Kepler Exoplanet Host Stars from Asteroseismology"

The research by Silva Aguirre et al. focuses on the asteroseismic analysis of 33 Kepler planet-candidate host stars. The primary objective is to derive accurate stellar properties, including ages, using a new Bayesian framework that processes individual oscillation frequencies, their combinations, and average asteroseismic parameters. This methodological approach aims to set a new standard in determining stellar characteristics with impressive precision.

Methodology and Data

The foundation of this research is the asteroseismic data from Kepler, which offers solar-like oscillation frequencies with sufficiently high signal-to-noise ratios. The paper introduces a Bayesian scheme capable of processing diverse asteroseismic inputs, such as individual oscillation frequencies and frequency combinations, alongside traditional average asteroseismic parameters. The authors employ grids of evolutionary models to derive stellar properties, boasting median statistical uncertainties of 1.2% for radius, 1.7% for density, 3.3% for mass, and 14% for age.

A major advantage of this paper is its incorporation of systematic effects from variations in model inputs such as solar abundances and the mixing-length parameter, demonstrating that these are generally smaller than the statistical uncertainties.

Numerical Precision and Systematics

The paper achieves an unprecedented precision in determining fundamental stellar parameters, representing a significant step forward in uniform determinations. The authors performed comprehensive assessments to identify potential systematic biases introduced by different evolutionary and pulsation codes. They found minor deviations, indicating robust outcomes irrespective of the computational approach.

Results and Discussion

Statistical and systematic analyses reveal that low-mass stars' ages are notably affected by microscopic diffusion, highlighting a consistent pattern of younger age estimates when diffusion is incorporated. For higher-mass stars, convective overshooting significantly alters the derived properties post-main-sequence when convective cores are pronounced.

Another key result is the excellent agreement between properties derived from individual frequency analysis and those obtained via global asteroseismic parameters. This finding confirms that scaling relations remain valid for main-sequence stars near solar conditions and can be reliable where individual frequency extraction is impractical. However, a slight systematic difference is observed when using global asteroseismic parameter scaling relations directly.

Implications and Future Prospects

The robust determination of stellar ages and parameters offers a valuable dataset for further exploration of dynamical processes in exoplanetary systems, including eccentricity and tidal interactions. The paper affirms the synergy between asteroseismology and exoplanet research, facilitating advances in both fields.

Ultimately, the paper's sophisticated methodological framework and comprehensive analysis provide a touchstone for subsequent large-scale asteroseismic studies of exoplanets, particularly as missions like TESS and PLATO extend exoplanet detections. The data and insights from this paper will likely form the groundwork for enhanced interpretations of exoplanet formation and evolution in diverse atmospheres across different stellar ages.

Given the precision and reliability achieved, this research is poised to influence theoretical models and observational strategies in stellar astrophysics and exoplanetology, feeding into ongoing efforts to explore the cosmos's rich tapestry with greater clarity.