2015MNRAS.447..680G

We intend to use stellar models with and without α-enhancement, as well as asteroseismic analysis, to study two α-enhanced stars, KIC 7976303 and KIC 8694723. For the α-enhanced models, we adopt [α/Fe] = 0.2 and 0.4. For the evolved subgiant KIC 7976303 with mixed modes, the α-enhanced models fit the observations better than the models without α-enhancement, and point to a star with M = 1.20±0.02M_☉, t = 4.88±0.08Gyr, R = 2.04±0.01 R_☉ and L = 5.07±0.05 L_☉. For the post turn-off star KIC 8694723, we find that the models fit the observations well in all three cases ([α/Fe] = 0.0, 0.2 and 0.4). According to the observed metal abundances, only α-enhanced models are used to estimate the stellar parameters, which are M = 1.13±0.06M_☉, t = 5.47±0.43Gyr, R = 1.55±0.13 R_☉ and L = 3.18±0.26 L_☉. Our α-enhanced models indicate that KIC 7976303 has a larger mass and younger age than in previous works based on standard models. Furthermore, the differences of estimated mass and age between the three cases are ∼ 0.1M_☉ and ∼ 0.5-1.3Gyr. These results suggest that we include α-enhancement in the modelling of α-enhanced stars, such as members of globular clusters and metal-poor stars in the disc and in the halo.