Asteroseismology of Exoplanet Host Stars

Asteroseismology of Exoplanet Host Stars

Authors:

Huber et al

Abstract:

Asteroseismology is among the most powerful observational tools to determine fundamental properties of stars. Space-based photometry has recently enabled the systematic detection of oscillations in exoplanet host stars, allowing a combination of asteroseismology with transit and radial-velocity measurements to characterize planetary systems. In this contribution I will review the key synergies between asteroseismology and exoplanet science such as the precise determination of radii and ages of exoplanet host stars, as well as applications of asteroseismology to measure spin-orbit inclinations in multiplanet systems and orbital eccentricities of small planets. Finally I will give a brief outlook on asteroseismic studies of exoplanet hosts with current and future space-based missions such as K2 and TESS.

Asteroseismology Tested Against SuperEarth/Mini Neptune Kepler-410/KOI-42

What asteroseismology can do for exoplanets

Authors:

Van Eylen et al

Abstract:

We describe three useful applications of asteroseismology in the context of exoplanet science: (1) the detailed characterisation of exoplanet host stars; (2) the measurement of stellar inclinations; and (3) the determination of orbital eccentricity from transit duration making use of asteroseismic stellar densities. We do so using the example system Kepler-410 (Van Eylen et al. 2014). This is one of the brightest (V = 9.4) Kepler exoplanet host stars, containing a small (2.8 Rearth) transiting planet in a long orbit (17.8 days), and one or more additional non-transiting planets as indicated by transit timing variations. The validation of Kepler-410 (KOI-42) was complicated due to the presence of a companion star, and the planetary nature of the system was confirmed after analyzing a Spitzer transit observation as well as ground-based follow-up observations.

Global Analysis of KOI-977

Global Analysis of KOI-977: Spectroscopy, Asteroseismology, and Phase-curve Analysis

Authors:

Hirano et al

Abstract:

We present a global analysis of KOI-977, one of the planet host candidates detected by {\it Kepler}. Kepler Input Catalog (KIC) reports that KOI-977 is a red giant, for which few close-in planets have been discovered. Our global analysis involves spectroscopic and asteroseismic determinations of stellar parameters (e.g., mass and radius) and radial velocity (RV) measurements. Our analyses reveal that KOI-977 is indeed a red giant in the red clump, but its estimated radius (≳20R⊙=0.093 AU) is much larger than KOI-977.01's orbital distance (∼0.027 AU) estimated from its period (Porb∼1.35 days) and host star's mass. RV measurements show a small variation, which also contradicts the amplitude of ellipsoidal variations seen in the light-curve folded with KOI-977.01's period. Therefore, we conclude that KOI-977.01 is a false positive, meaning that the red giant, for which we measured the radius and RVs, is different from the object that produces the transit-like signal (i.e., an eclipsing binary). On the basis of this assumption, we also perform a light-curve analysis including the modeling of transits/eclipses and phase-curve variations, adopting various values for the dilution factor D, which is defined as the flux ratio between the red giant and eclipsing binary. Fitting the whole folded light-curve as well as individual transits in the short cadence data simultaneously, we find that the estimated mass and radius ratios of the eclipsing binary are consistent with those of a solar-type star and a late-type star (e.g., an M dwarf) for D≳20.

HD 52265 is 2.1 to 2.45 Billion Years Old

Asteroseismology for "à la carte" stellar age-dating and weighing: Age and mass of the CoRoT exoplanet host HD 52265

Authors:

Lebreton et al

Abstract:

In the context of CoRoT, Kepler, Gaia, TESS, and PLATO, precise and accurate stellar ages, masses and radii are of paramount importance. They are crucial to constrain scenarii of planetary formation and evolution.We aim at quantifying how detailed stellar modeling improves the accuracy and precision on age and mass of individual stars. We adopt a multifaceted approach where we examine how the number of observational constraints as well as the uncertainties on observations and on model input physics impact the age-dating and weighing. We modelled the exoplanet host-star HD52265, a MS, solar-like oscillator observed by CoRoT. We considered different sets of observational constraints (HR data, metallicity, seismic constraints). For each case, we determined the age, mass, and properties of HD52265 inferred from models, and quantified the impact of the models inputs. Our seismic analysis provides an age A=2.10-2.54 Gyr, a mass M=1.14-1.32 Msun, and a radius R=1.30-1.34 Rsun, which corresponds to uncertainties of 10, 7, and 3% respectively. Our seismic study provides constraints on surface convection, through the mixing-length found to be 12-15% smaller than the solar one. Because of helium-mass degeneracy, the initial He abundance is determined modulo the mass. The seismic mass of the exoplanet is found to be Mp sin i=1.17-1.26 MJup, much more precise than what can be derived by HR diagram inversion. We demonstrate that asteroseismology allows to improve the age accuracy compared to other methods. We emphasize that the knowledge of the mean properties of oscillations -as the large frequency separation- is not enough for deriving accurate ages. We need precise individual frequencies to narrow the age scatter due to model uncertainties. This strengthen the case for precise classical stellar parameters and frequencies as will be obtained by Gaia and PLATO.