SpaceInn hare-and-hounds exercise: Estimation of stellar properties using space-based asteroseismic data

Abstract

Context. Detailed oscillation spectra comprising individual frequencies for numerous solar-type stars and red giants are either currently available, e.g. courtesy of the CoRoT, Kepler, and K2 missions, or will become available with the upcoming NASA TESS and ESA PLATO 2.0 missions. The data can lead to a precise characterisation of these stars thereby improving our understanding of stellar evolution, exoplanetary systems, and the history of our galaxy. Aims. Our goal is to test and compare different methods for obtaining stellar properties from oscillation frequencies and spectroscopic constraints. Specifically, we would like to evaluate the accuracy of the results and reliability of the associated error bars, and to see where there is room for improvement. Methods. In the context of the SpaceInn network, we carried out a hare-and-hounds exercise in which one group, the hares, simulated observations of oscillation spectra for a set of ten artificial solar-type stars, and a number of hounds applied various methods for characterising these stars based on the data produced by the hares. Most of the hounds fell into two main groups. The first group used forward modelling (i.e. applied various search/optimisation algorithms in a stellar parameter space) whereas the second group relied on acoustic glitch signatures. Results. Results based on the forward modelling approach were accurate to 1.5% (radius), 3.9% (mass), 23% (age), 1.5% (surface gravity), and 1.8% (mean density), as based on the root mean square difference. Individual hounds reached different degrees of accuracy, some of which were substantially better than the above average values. For the two 1 M stellar targets, the accuracy on the age is better than 10% thereby satisfying the requirements for the PLATO 2.0 mission. High stellar masses and atomic diffusion (which in our models does not include the effects of radiative accelerations) proved to be sources of difficulty. The average accuracies for the acoustic radii of the base of the convection zone, the He II ionisation, and the Γ 1 peak located between the two He ionisation zones were 17%, 2.4%, and 1.9%, respectively. The results from the forward modelling were on average more accurate than those from the glitch fitting analysis as the latter seemed to be affected by aliasing problems for some of the targets. Conclusions. Our study indicates that forward modelling is the most accurate way of interpreting the pulsation spectra of solar-type stars. However, given its model-dependent nature, this method needs to be complemented by model-independent results from, e.g. glitch analysis. Furthermore, our results indicate that global rather than local optimisation algorithms should be used in order to obtain robust error bars.

Standing on the Shoulders of Dwarfs: the Kepler Asteroseismic LEGACY Sample. II. Radii, Masses, and Ages

“…2, the results for radius and mass also reveal some differences between the pipelines: C2kSMO has much larger radius uncertainties and formal mass errors only slightly smaller than the rest of the methods, resulting in the large density fractional uncertainties. Age distributions show some pipelines with fractional errors below 10% (C2kSMO and GOE) while the rest encompass values between 10-30%, which is in much better agreement with the level of age uncertainties determined from hare-and-hounds exercises (Reese et al 2016) and those normally obtained from individual frequency fitting of Kepler main-sequence targets (e.g., Mathur et al 2012;Silva Aguirre et al 2013;Lund et al 2014;Lebreton & Goupil 2014;Silva Aguirre et al 2015).…”

“…The stellar and oscillation mode properties presented here and in the accompanying paper by Lund et al (2016, submitted) constitute the largest sample of asteroseismically-analysed main-sequence stars using individual oscillation frequencies. Adding the stars studied by Davies et al (2016) andSilva Aguirre et al (2015) gives 99 stars that comprise the best-characterised set of main-sequence solar-like oscillators observed by the Kepler mission. We have compared of our determined initial abundances with expectations from galactic chemical enrichment, and of our obtained efficiencies of convection with predictions from 3D hydrodynamical simulations.…”

“…Silva Aguirre et al (2015) and Davies et al (2016) analysed and modelled a sample of 33 exoplanet hosts for which the Kepler mission had obtained asteroseismic data, including individual oscillation frequencies. Those results have informed other studies of exoplanet systems (e.g., Van Eylen & Albrecht 2015;Bonfanti et al 2016;Jontof-Hutter et al 2016), and of the relation between stellar rotation and age (van Saders et al 2016).…”

PLATO Hare-and-Hounds exercise: Asteroseismic model fitting of main-sequence solar-like pulsators

“…Nevertheless, these tests are useful to understand the biases that are introduced in the inferred stellar properties by known sources of systematic errors, which can be accounted for in the simulations. Exercises of this type have been performed earlier both based on simulated data sets including only global seismic observations (Stello et al 2009) and simulated data sets including individual-mode frequencies (Reese et al 2016). Nevertheless, in both cases the underlying stellar models and associated models' physics varied according to the modeller's choice, hindering a direct comparison of the different inference procedures.…”

Inverse Problems in Asteroseismology

“…Author G.C.A. perturbed the "observations" of these models according to the scheme devised by Reese et al (2016). Appendix 2.6.5 lists the true values and the perturbed observations of the hare-and-hound models.…”