Spectroscopy of dwarf stars around the north celestial pole

Abstract

New space missions (e.g., NASA-TESS and ESA-PLATO) will perform an in-depth analysis of bright stars in large fields of the celestial sphere searching for extraterrestrial planets and investigating their host-stars. Asteroseismic observations will search for exoplanet-hosting stars with solar-like oscillations. In order to achieve all the goals, a full characterization of the stellar objects is important. However, accurate atmospheric parameters are available for less than 30% of bright dwarf stars of the solar neighborhood. In this study we observed high-resolution (R = 60,000) spectra for all bright (V<8 mag) and cooler than F5 spectral class dwarf stars in the northern-most field of the celestial sphere with radius of 20° from the α(2000)=161°.03 and δ(2000)=86°.60 that is a center of one of the preliminary ESO-PLATO fields. Spectroscopic atmospheric parameters were determined for 140slowly rotating stars, for 73% of them for the first time. The majority (83%) of the investigated stars are in the TESS object lists and all of them are in the preliminary PLATO field. Our results have no systematic differences when compared with other recent studies. We have 119 stars in common with the Geneva–Copenhagen Survey, where stellar parameters were determined photometrically, and find a 14±125K difference in effective temperatures, 0.01±0.16 in log g, and −0.02±0.09dex in metallicities. Comparing our results for 39 stars with previous high-resolution spectral determinations, we find only a 7±73K difference in effective temperatures, 0.02±0.09 in log g, and −0.02±0.09dex in metallicities. We also determined basic kinematic and orbital parameters for this sample of stars. From the kinematical point of view, almost all our stars belong to the thin disk substructure of the MilkyWay. The derived galactocentric metallicity gradient is −0.066±0.024dexkpc−1 (2.5σ significance) and the vertical metallicity gradient is −0.102±0.099dexkpc−1 (1σ significance) that comply with the latest inside-out thin disk formation models, including those with stellar migration taken into account.