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The Transiting Exoplanet Survey Satellite (TESS) is performing a near all-sky survey for planets that transit bright stars. It provides excellent photometric data for asteroseismology of solar-like stars that exhibit oscillation by a convection-driven mechanism. In this paper, we analyze the light curves of 14 stars that are observed by TESS. These stars mainly focus on Sector 21 and the other Sectors intersecting with Sector 21. Through crossmatching with the LAMOST surveys, 14 stars with signals of solar-like oscillations are selected, and asteroseismic analysis is present. The frequency of maximum power ν max and the large frequency separation Δν are extracted from its frequency power spectrum using the pySYD pipeline. Scaling relations are an attractive method that can easily and immediately be applied to observations to derive the stellar properties. To validate the different calibrated scaling relations for 14 TESS stars, the fundamental stellar properties are estimated by the relations and compared with grid-based modeling results, which use the constraints of global asteroseismic parameters and nonasteroseismic parameters. The new red-giant branch (RGB) scaling relations are found to overestimate the radius and mass when compared to the grid results, while the f Δν scaling relations lead to overall lower radius and mass estimates. The average uncertainties of these stars from grid modeling are within 2% in the radius and 3% in the mass. Regardless of the method, we can get almost equally good results of log g for all the stars. Besides the grid method, the new RGB scaling relations for ages provide a simple and accurate method to determine the stellar ages.

We present an asteroseismic analysis of the Kepler light curve of MC 8263801, a red-giant star in the open cluster NGC 6866 that has previously been reported to be a helium-burning red-clump (RC) star. We extracted the frequencies of the radial and quadrupole modes from its frequency power spectrum and determined its properties using a grid of evolutionary models constructed with MESA. The oscillation frequencies were calculated using the GYRE code and the surface term was corrected using the Ball & Gizon prescription. We find that the star has a mass of M/M-circle dot = 1.793 +/- 0.072, age t = 1.48 +/- 0.21 Gyr, and radius R/R-circle dot = 10.53 +/- 0.28. By analyzing the internal structure of the best-fitting model, we infer the evolutionary status of the star MC 8263801 as being on the ascending part of the red-giant branch, and not on the RC. This result is verified using a purely asteroseismic diagnostic, the epsilon(c) - Delta nu(c), diagram which can distinguish red-giant branch stars from red-clump stars. Finally, by comparing its age with NGC 6866 (t = 0.65 +/- 0.1 Gyr), we conclude that KIC 8263801 is not a member of this open cluster.

The "bump" is a prominent feature of the red giant branch (RGB) luminosity function of stellar clusters. Through constructing a grid of models with different masses and metallicities to study the feature of the RGB bump luminosity we find that the luminosity increases almost monotonically with increasing mass for a given metallicity and decreases monotonically with increasing metallicity. Moreover, different stars have different shapes of the RGB bump. It is correlated with the sharpness of the H discontinuity, which is left over by the convection envelope during the first dredge-up. Using the periodicity in the small separations d(01), d(10) to probe the internal structure, we find that, at about half the acoustic radius, the sound speed has a sharp variation that is caused by a local depression of the first adiabatic exponent Gamma(1) in the second helium ionization zone. It induces an oscillation modulation in d(01), d(10) with a period of 6.4 mu Hz. Meanwhile, in the same model, the base of the convective envelope is located at a relatively small acoustic radius t(envp)/T, which is about 10(-1). It is too deep to detect the exact location of the bottom of the outer convective envelope. In order to discriminate the evolutionary status of different stars, we calculate the asymptotic g-mode period spacing Delta Pi(1). We find that Delta Pi(1) decreases monotonically with evolution. It is a reliable parameter for distinguishing stars in different positions of the RGB bump.

NASA's Kepler mission is providing basic asteroseismic data for hundreds of stars. One of the more common ways of determining stellar characteristics from these data is by so-called "grid based" modelling. We have made a detailed study of grid-based analysis techniques to study the errors (and error-correlations) involved. As had been reported earlier, we find that it is relatively easy to get very precise values of stellar radii using grid-based techniques. However, we find that there are small, but significant, biases that can result because of the grid of models used. The biases can be minimized if metallicity is known. Masses cannot be determined as precisely as the radii, and suffer from larger systematic effects. We also find that the errors in mass and radius are correlated. A positive consequence of this correlation is that log g can be determined both precisely and accurately with almost no systematic biases. Radii and log g can be determined with almost no model dependence to within 5% for realistic estimates of error in asteroseismic and conventional observations. Errors in mass can be somewhat higher unless accurate metallicity estimates are available. Age estimates of individual stars are the most model dependent. The errors are larger too. However, we find that for star-clusters, it is possible to get a relatively precise age if one assumes that all stars in a given cluster have the same age., Comment: ApJ, in press