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=60000) 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 degrees from the α(2000) = 161.03 • and δ(2000) = 86.60 • that is a centre of one of the preliminary ESO-PLATO fields. Spectroscopic atmospheric parameters were determined for 140 slowly 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 ± 125 K difference in effective temperatures, 0.01 ± 0.16 in log g, and −0.02 ± 0.09 dex in metallicities. Comparing our results for 39 stars with previous high-resolution spectral determinations, we find only a 7 ± 73 K difference in effective temperatures, 0.02 ± 0.09 in log g, and −0.02 ± 0.09 dex 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 Milky Way. The derived galactocentric metallicity gradient is −0.066 ± 0.024 dex kpc −1 (2.5 σ significance) and the vertical metallicity gradient is −0.102 ± 0.099 dex kpc −1 (1σ significance) that comply with the latest inside-out thin disk formation models, including those with stellar migration taken into account.

High-resolution Spectroscopic Study of Dwarf Stars in the Northern Sky: Lithium, Carbon, and Oxygen Abundances

“…From this survey, we took a data set consisting of 249 F, G, and K spectral type dwarf and subgiant stars observed in 2017-2018. The reader is directed to the papers by Mikolaitis et al (2018Mikolaitis et al ( , 2019 for a more detailed description of the observations, data reduction, determination of the main atmospheric parameters, stellar ages, and detailed abundances for 17 elements (Na, Mg, Al, Si, S, K, Ca, Sc, Ti, Vi, Cr, Mn, Fe, Co, Ni, Cu, and Zn). Like in the previous papers, we used a spectral synthesis method and the code TURBOSPECTRUM (Alvarez & Plez 1998) with the MARCS stellar atmospheric models (Gustafsson et al 2008).…”

High-resolution spectroscopic study of dwarf stars in the northern sky

“…In the era of the new extra-solar planet hunting telescopes such as ESA's PLAnetary Transits and Oscillations of stars (PLATO) or NASA's Transiting Exoplanet Survey Satellite (TESS), it is very important to obtain as much information as possible on the stars they will be observing. These missions in particular will focus on the northern sky (see Mikolaitis et al 2018 for the overview of the project, hereafter Paper I).…”

Search for variable stars in the northern sky: analysis of photometric time series for 3598 stars

“…This work is part of our Spectroscopic and photometric survey of the northern sky (SPFOT; Mikolaitis et al 2018;Pakštienė et al 2018) started at the Molėtai Astronomical Observatory (MAO) in 2016. It aims to deliver a full spectroscopic characterisation and variability information of the brightest stars in the northern sky.…”