M.S.Xiang, X.F.Zhang,T.D.Li,S.L.Bi,X.W.Liu,Y.Huang,J.N.Fu,K.Liu,Z.J.Tian,Z.S.Ge,J.H.Zhang

Main sequence turn-off (MSTO) stars are advantaged indicators of Galactic evo- lution since their ages could be robustly estimated by atmospheric parameters. Hundreds of thousands of MSTO stars have been selected from the LAMOST Galactic survey to study the evolution of the Galaxy, and it will be benefited from accurate estimates of stellar param- eters. In this work, we select 150 MSTO candidates in the LAMOST MSTO stars sample and constrain their stellar parameters with theoretical models. Asteroseismic properties ∆ν, νmaxobtained from Kepler data are considered for accurate estimates. And furthermore, we examine the contamination rate of the LAMOST MSTO stars sample and validate the age estimation by the LAMOST spectra in Xiang et al. (2015). The results show that 79 of the candidates are MSTO stars and others are main-sequence stars or sub giants and a comparison between ages from this work and what have been obtained through interpolation method in Xiang et al. (2015) shows that there is a mean difference of 0.53 Gyr (7%) and a dispersion of 2.71 Gyr (28%). A considerable fraction of oldest stars in the LAMOST MSTO stars sample are likely contamination stars from much younger dwarf/subgiant stars. The main cause for high contamination rates are likely relatively large systematic bias of surface gravity and may not be ignored in the study of Galactic structure.