Asteroseismic analysis of solar-mass subgiants KIC 6442183 and KIC 11137075 observed by Kepler

¹ Department of Astronomy, Beijing Normal University, 100875 Beijing, PR China
e-mail: tianzhijia@mail.bnu.edu.cn; bisl@bnu.edu.cn
² Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006, Australia
e-mail: t.bedding@physics.usyd.edu.au
³ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark

Received: 26 February 2015
Accepted: 1 June 2015

Abstract

Context. Asteroseismology provides a powerful way to constrain stellar parameters. Solar-like oscillations have been observed on subgiant stars with the Kepler mission. The continuous and high-precision time series enables us to carry out a detailed asteroseismic study for these stars.

Aims. We carry out data processing of two subgiants of spectral type G: KIC 6442183 and KIC 11137075 observed with the Kepler mission, and perform seismic analysis for the two evolved stars.

Methods. We estimated the global asteroseismic parameters Δν = 64.9 ± 0.2 μHz and ν_max = 1225 ± 17 μHz for KIC 6442183, Δν = 65.5 ± 0.2 μHz and ν_max = 1171 ± 8μHz for KIC 11137075, respectively. In addition, we extracted the individual mode frequencies of the two stars. We compared stellar models and observations, including mode frequencies and mode inertias. The mode inertias of mixed modes, which are sensitive to the stellar interior, were used to constrain stellar models. We defined a quantity dν_m−p that measures the difference between the mixed modes and the expected pure pressure modes, which is related to the inertia ratio of mixed modes to radial modes.

Results. Asteroseismic together with spectroscopic constraints provide the estimates of the stellar parameters: M = 1.04_-0.04^{+ 0.01} M_⊙, R = 1.66_-0.02^{+ 0.01}R_⊙ and t = 8.65_-0.06^+1.12 Gyr for KIC 6442183, and M = 1.00_-0.01^{+ 0.01} M_⊙, R = 1.63_-0.01^{+ 0.01}R_⊙ and t = 10.36_-0.20^+0.01 Gyr for KIC 11137075. Either mode inertias or dν_m−p can be used to constrain stellar models.