Activity and the Li abundances in the FGK dwarfs

Abstract

Aims. The aim of the present study is to determine the Li abundances for a large set of the FGK dwarfs and to analyse the connections between the Li content, stellar parameters, and activity. Methods. The atmospheric parameters, rotational velocities and the Li abundances were determined from a homogeneous collection of the echelle spectra with high resolution and a high signal-to-noise ratio. The rotational velocities v sin i were determined by calibrating the cross-correlation function. The effective temperatures T eff were estimated by the line-depth ratio method. The surface gravities log g were computed by two methods: the iron ionization balance and the parallax. The LTE Li abundances were computed using synthetic spectra method. The behaviour of the Li abundance was examined in correlation with T eff , [Fe/H], as well as with v sin i and the level of activity in three stellar groups of the different temperature range. Results. The stellar parameters and the Li abundances are presented for 150 slow rotating stars of the lower part of the main sequence. The studied stars show a decline in the Li abundance with decreasing temperature T eff and a significant spread, which should be due to the difference of age of stars. The correlations between the Li abundances, rotational velocities v sin i, and the level of the chromospheric activity were discovered for the stars with 6000 > T eff > 5700 K, and it is tighter for the stars with 5700 > T eff > 5200 K. The target stars with T eff < 5200 K do not show any correlation between log A(Li) and v sin i. The relationship between the chromospheric and coronal fluxes in active with detected Li as well as in less active stars gives a hint that there exist different conditions in the action of the dynamo mechanism in those stars. Conclusions. We found that the Li-activity correlation is evident only in a restricted temperature range and the Li abundance spread seems to be present in a group of low chromospheric activity stars that also show a broad spread in the chromospheric vs. coronal activity.

LACEwING: A New Moving Group Analysis Code

“…Some genuinely young stars at the fully convective boundary around spectral type M3V are excluded from this sample because lithium is fully depleted at their ages, while some more massive stars still maintain lithium even at old ages (e.g., α Cen AB; Mishenina et al 2012). The sample can be found in the "LiSample" column of the Catalog of Suspected Nearby Young Stars, where system primaries that qualify for the lithium sample are flagged with "L," system primaries that qualify for the lithium sample but have membership in a more distant group are flagged with "F," and primaries that do not have lithium but have a companion that qualifies are flagged with "A."…”

The HARPS-N Rocky Planet Search

“…Over the past few years, the star has been the object of several studies aiming at determining photospheric parameters and chemical abundance analyses (Valenti & Fischer 2005;Mishenina et al 2008Mishenina et al , 2012Kovtyukh et al 2003;Ramírez et al 2013;Prugniel et al 2011). Results of these studies are given in Table 2 for comparison.…”

Influence of Rotation on Stellar Evolution

“…Standard stellar evolution models account for microscopic diffusion processes that may occur on long time scales in radiative regions such as gravitational settling or radiative levitation. Mokiem et al 2006); e Li abundances as a function of T eff for a sample of dwarfs and subgiants in the Galaxy (from Mishenina et al 2012); f Nitrogen abundances in O-type stars of the SMC (from Heap et al 2006) (including NeNa-and MgAl-chains) can be used to trace internal mixing when variations are observed at evolutionary phases where they are not expected from standard stellar evolution models. In red giant stars, the presence of s-process 2 at the surface may also be considered as evidence for internal mixing.…”

“…• Lithium depletion during phases where no convective dredge-up is expected −→ in low-and intermediate-mass stars (Boesgaard 1989, Boesgaard & Tripicco 1986, Gratton et al 2000, Baumann et al 2010, Canto Martins et al 2011Mishenina et al 2012 • Lithium enrichment −→ in low-and intermediate-mass stars (Charbonnel & Balachandran 2000, Lèbre et al 2009 • Boron and Beryllium depletion −→ in low-, intermediate-mass, and massive stars (Boesgaard 2005, Boesgaard et al 2005a, Boesgaard & Krugler Hollek 2009 • Carbon depletion and carbon isotopic ratio decrease −→ in low-mass red giant stars, in main sequence and post main sequence massive stars (Gratton et al 2000) • Nitrogen enrichment −→ in low-mass red giant stars, in main sequence and post main sequence massive stars (Frebel et al 2005, Heap et al 2006, Martins et al 2009 • Helium enrichment −→ in massive O-type stars at low metallicity (Mokiem et al 2006) • s-process elements enrichment −→ in intermediate-mass AGB stars…”