The LAMOST spectroscopic survey of stars in the Kepler field of view: Activity indicators and stellar parameters

We summarize the results of the completed first round of the LAMOST-Kepler project, and describe the status of its on-going second round. As a result of the first round of this project, the atmospheric parameters (T eff , log g , and [Fe/H]), the spectral classification (spectral type and luminosity class), and the radial velocities (RV ) have been measured for 51,385 stars. For 4031 stars, we were able to measure the projected rotational velocity, while the minimum detectable v sin i was 120 km s−1 . For 8821 stars with more than one observation, we computed the χ -square probability that the detected RV variations have a random occurrence. Finally, we classified 442 stars as chromospherically active on the basis of the analysis of their Hα and Ca II-IRT fluxes. All our results have been obtained from the low-resolution (R ∼ 1800) spectroscopic observations acquired with the LAMOST instrument

A Revised Effective Temperature Scale for the Kepler Input Catalog

We present a catalog of revised effective temperatures for stars observed in long-cadence mode in the Kepler Input Catalog (KIC). We use SDSS griz filters tied to the fundamental temperature scale. Polynomials for griz color-temperature relations are presented, along with correction terms for surface gravity effects, metallicity, and statistical corrections for binary companions or blending. We compare our temperature scale to the published infrared flux method (IRFM) scale for VJKs in both open clusters and the Kepler fields. We find good agreement overall, with some deviations between (J - Ks)-based temperatures from the IRFM and both SDSS filter and other diagnostic IRFM color-temperature relationships above 6000 K. For field dwarfs we find a mean shift towards hotter temperatures relative to the KIC, of order 215 K, in the regime where the IRFM scale is well-defined (4000 K to 6500 K). This change is of comparable magnitude in both color systems and in spectroscopy for stars with Teff below 6000 K. Systematic differences between temperature estimators appear for hotter stars, and we define corrections to put the SDSS temperatures on the IRFM scale for them. When the theoretical dependence on gravity is accounted for we find a similar temperature scale offset between the fundamental and KIC scales for giants. We demonstrate that statistical corrections to color-based temperatures from binaries are significant. Typical errors, mostly from uncertainties in extinction, are of order 100 K. Implications for other applications of the KIC are discussed.Comment: Corrected for sign flip errors in the gravity corrections. Erratum to this paper is attached in Appendix. Full version of revised Table 7 can be found at http://home.ewha.ac.kr/~deokkeun/kic/sdssteff_v2.dat.g

An asteroseismic membership study of the red giants in three open clusters observed by Kepler: NGC6791, NGC6819, and NGC6811

Studying star clusters offers significant advances in stellar astrophysics due to the combined power of having many stars with essentially the same distance, age, and initial composition. This makes clusters excellent test benches for verification of stellar evolution theory. To fully exploit this potential, it is vital that the star sample is uncontaminated by stars that are not members of the cluster. Techniques for determining cluster membership therefore play a key role in the investigation of clusters. We present results on three clusters in the Kepler field of view based on a newly established technique that uses asteroseismology to identify fore- or background stars in the field, which demonstrates advantages over classical methods such as kinematic and photometry measurements. Four previously identified seismic non-members in NGC6819 are confirmed in this study, and three additional non-members are found -- two in NGC6819 and one in NGC6791. We further highlight which stars are, or might be, affected by blending, which needs to be taken into account when analysing these Kepler data.Comment: 12 pages, 9 figures, 5 tables, accepted by Ap

Kepler-21b: A 1.6REarth Planet Transiting the Bright Oscillating F Subgiant Star HD 179070

We present Kepler observations of the bright (V=8.3), oscillating star HD 179070. The observations show transit-like events which reveal that the star is orbited every 2.8 days by a small, 1.6 R_Earth object. Seismic studies of HD 179070 using short cadence Kepler observations show that HD 179070 has a frequencypower spectrum consistent with solar-like oscillations that are acoustic p-modes. Asteroseismic analysis provides robust values for the mass and radius of HD 179070, 1.34{\pm}0.06 M{\circ} and 1.86{\pm}0.04 R{\circ} respectively, as well as yielding an age of 2.84{\pm}0.34 Gyr for this F5 subgiant. Together with ground-based follow-up observations, analysis of the Kepler light curves and image data, and blend scenario models, we conservatively show at the >99.7% confidence level (3{\sigma}) that the transit event is caused by a 1.64{\pm}0.04 R_Earth exoplanet in a 2.785755{\pm}0.000032 day orbit. The exoplanet is only 0.04 AU away from the star and our spectroscopic observations provide an upper limit to its mass of ~10 M_Earth (2-{\sigma}). HD 179070 is the brightest exoplanet host star yet discovered by Kepler.Comment: Accepted to Ap

The LAMOST spectroscopic survey of stars in the

We summarize the results of the completed first round of the LAMOST-Kepler project, and describe the status of its on-going second round. As a result of the first round of this project, the atmospheric parameters (Teff, log g, and [Fe/H]), the spectral classification (spectral type and luminosity class), and the radial velocities (RV) have been measured for 51,385 stars. For 4031 stars, we were able to measure the projected rotational velocity, while the minimum detectable v sin i was 120 km s−1. For 8821 stars with more than one observation, we computed the χ-square probability that the detected RV variations have a random occurrence. Finally, we classified 442 stars as chromospherically active on the basis of the analysis of their Hα and Ca II-IRT fluxes. All our results have been obtained from the low-resolution (R ∼ 1800) spectroscopic observations acquired with the LAMOST instrument

A SUPER-SOLAR METALLICITY FOR STARS WITH HOT ROCKY EXOPLANETS

Host star metallicity provides a measure of the conditions in protoplanetary disks at the time of planet formation. Using a sample of over 20,000 Kepler stars with spectroscopic metallicities from the LAMOST survey, we explore how the exoplanet population depends on host star metallicity as a function of orbital period and planet size. We find that exoplanets with orbital periods less than 10 days are preferentially found around metal-rich stars ([Fe/H] similar or equal to 0.15 +/- 0.05 dex). The occurrence rates of these hot exoplanets increases to similar to 30% for super-solar metallicity stars from similar to 10% for stars with a sub-solar metallicity. Cooler exoplanets, which reside at longer orbital periods and constitute the bulk of the exoplanet population with an occurrence rate of greater than or similar to 90%, have host star metallicities consistent with solar. At short orbital periods, P < 10 days, the difference in host star metallicity is largest for hot rocky planets (< 1.7 R-circle plus), where the metallicity difference is [Fe/H] similar or equal to 0.25 +/- 0.07 dex. The excess of hot rocky planets around metal-rich stars implies they either share a formation mechanism with hot Jupiters, or trace a planet trap at the protoplanetary disk inner edge, which is metallicity dependent. We do not find statistically significant evidence for a previously identified trend that small planets toward the habitable zone are preferentially found around low-metallicity stars. Refuting or confirming this trend requires a larger sample of spectroscopic metallicities.NASA; National Aeronautics and Space Administration [NNX15AD94G]; [NCN 2014/13/B/ST9/00902]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]