* Astronomy

Title: Characterising two solar-type Kepler subgiants with asteroseismology: KIC10920273 and KIC11395018
Authors: G. Dogan, T. S. Metcalfe, S. Deheuvels, M. P. Di Mauro, P. Eggenberger, O. L. Creevey, M. J. P. F. G. Monteiro, M. Pinsonneault, A. Frasca, C. Karoff, S. Mathur, S. G. Sousa, I. M. Brandao, T. L. Campante, R. Handberg, A.O. Thygesen, K. Biazzo, H. Bruntt, E. Niemczura, T. R. Bedding, W. J. Chaplin, J. Christensen-Dalsgaard, R. A. Garcia, J. Molenda-Zakowicz, D. Stello, J. L. Van Saders, H. Kjeldsen, M. Still, S. E. Thompson, J. Van Cleve

Determining fundamental properties of stars through stellar modelling has improved substantially due to recent advances in asteroseismology. Thanks to the unprecedented data quality obtained by space missions, particularly CoRoT and Kepler, invaluable information is extracted from the high-precision stellar oscillation frequencies, which provide very strong constraints on possible stellar models for a given set of classical observations. In this work, we have characterised two relatively faint stars, KIC10920273 and KIC11395018, using oscillation data from Kepler photometry and atmospheric constraints from ground-based spectroscopy. Both stars have very similar atmospheric properties; however, using the individual frequencies extracted from the Kepler data, we have determined quite distinct global properties, with increased precision compared to that of earlier results. We found that both stars have left the main sequence and characterised them as follows: KIC10920273 is a one-solar-mass star (M=1.00 ±0.04 solar masses), but much older than our Sun (t=7.12 ±0.47 Gyr), while KIC11395018 is significantly more massive than the Sun (M=1.27 ±0.04 solar masses) with an age close to that of the Sun (t=4.57 ±0.23 Gyr). We confirm that the high lithium abundance reported for these stars should not be considered to represent young ages, as we precisely determined them to be evolved subgiants. We discuss the use of surface lithium abundance, rotation and activity relations as potential age diagnostics.

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