Radius Determination of Solar-Type Stars Using Asteroseismology: What to Expect From the Kepler Mission

Abstract

For distant stars, as observed by the NASA Kepler satellite, parallax information is currently of fairly low quality and is not complete. This limits the precision with which the absolute sizes of the stars and their potential transiting planets can be determined by traditional methods. Asteroseismology will be used to aid the radius determination of stars observed during NASA's Kepler mission. We report on the recent asteroFLAG hare-and-hounds Exercise#2, where a group of 'hares' simulated data of F-K main-sequence stars that a group of 'hounds' sought to analyze, aimed at determining the stellar radii. We investigated stars in the range 9 < V < 15, both with and without parallaxes. We further test different uncertainties in T eff , and compare results with and without using asteroseismic constraints. Based on the asteroseismic large frequency spacing, obtained from simulations of 4-year time series data from the Kepler mission, we demonstrate that the stellar radii can be correctly and precisely determined, when combined with traditional stellar parameters from the Kepler Input Catalogue. The radii found by the various methods used by each independent hound generally agree with the true values of the artificial stars to within 3%, when the large frequency spacing is used. This is 5-10 times better than the results where seismology is not applied. These results give strong confidence that radius estimation can be performed to better than 3% for solar-like stars using automatic pipeline reduction. Even when the stellar distance and luminosity are unknown we can obtain the same level of agreement. Given the uncertainties used for this exercise we find that the input log g and parallax do not help to constrain the radius, and that T eff and metallicity are the only parameters we need in addition to the large frequency spacing. It is the uncertainty in the metallicity that dominates the uncertainty in the radius.

The underlying physical meaning of theνmax − νcrelation

“…More recently, the spacemissions CoRoT and Kepler confirmed those results by providing accurate and homogeneous measurements for a large sample of stars from red giants to main-sequence stars (e.g., Mosser et al 2010). Scaling relations are essential to study a large set of stars (e.g., Kallinger et al 2009;Stello et al 2009b) for which, in general, little is known, to provide a first order estimate for mass and radius (e.g., Basu et al 2010;Mosser et al 2010), or to probe the populations of red giants (Miglio et al 2009). …”

Fundamental properties of fiveKeplerstars using global asteroseismic quantities and ground-based observations

“…In preparation for the hundreds of stars in the Kepler data where these seismic parameters are readily available, several pipeline codes have been developed to use stellar models to infer the surface gravity log g, mean density ρ , radius R, mass M, and age τ of stars from the global seismic quantities supplemented with atmospheric parameters, such as T eff . In this analysis we used the following methods which are discussed below: CESAM2k/Mumbai (Mazumdar 2005), YaleBirmingham Gai et al 2011), RADIUS (Stello et al 2009a;Metcalfe et al 2010), SEEK , and RadEx10 (Creevey, in prep.). We used five different analysis methods in order to test the validity of our results, and to assess the performance of each code for producing reliable stellar parameters.…”

“…However, when oscillation frequencies are not available, grid-based methods still provide reliable estimates of the mean density, surface gravity, radius, and mass. For example, Stello et al (2009a) compared the radius determined from different automatic analyses using simulated data and find that the radius can be determined with a precision of 3%. Gai et al (2011) made a detailed study of grid-based methods for asteroseismology using simulated data and also solar data.…”

Seismic studies of planet-harbouring stars

“…This is the case for the "asteroFLAG" team sponsored by the International Space Science Institute (ISSI) in Bern, Switzerland (Chaplin et al 2008, Stello et al 2009, Mathur et al 2010, Benomar et al 2012. They showed, for example, that the radius of the star may be derived with an accuracy of a few percent with knowledge of the large separation only.…”