The Penn State − Toruń Centre for Astronomy Planet Search stars

Abstract

Context. Standard stellar evolution theory does not predict existence of Li-rich giant stars. Several mechanisms for Li-enrichment have been proposed to operate at certain locations inside some stars. The actual mechanism operating in real stars is still unknown. Aims. Using the sample of 348 stars from the Penn State − Toruń Centre for Astronomy Planet Search, for which uniformly determined atmospheric parameters are available, with chemical abundances and rotational velocities presented here, we investigate various channels of Li enrichment in giants. We also study Li-overabundant giants in more detail in search for origin of their peculiarities. Methods. Our work is based on the Hobby-Eberly Telescope spectra obtained with the High Resolution Spectrograph, which we use for determination of abundances and rotational velocities. The Li abundance was determined from the 7 Li λ670.8 nm line, while we use a more extended set of lines for α-elements abundances. In a series of Kolmogorov-Smirnov tests, we compare Li-overabundant giants with other stars in the sample. We also use available IR photometric and kinematical data in search for evidence of mass-loss. We investigate properties of the most Li-abundant giants in more detail by using multi-epoch precise radial velocities. Results. We present Li and α-elements abundances, as well as rotational velocities for 348 stars. We detected Li in 92 stars, of which 82 are giants. Eleven of them show significant Li abundance A(Li) NLTE > 1.4 and seven of them are Li-overabundant objects, according to common criterion of A(Li) > 1.5 and their location on HR diagram, including TYC 0684-00553-1 and TYC 3105-00152-1, which are two giants with Li abundances close to meteoritic level. For another 271 stars, upper limits of Li abundance are presented. We confirmed three objects with increased stellar rotation. We show that Li-overabundant giants are among the most massive stars from our sample and show larger than average effective temperatures. They are indistinguishable from the complete sample in terms of their distribution of luminosity, metallicity, rotational velocities, and α-elements abundances. Our results do not point out to one specific Li-enrichment mechanism operating in our sample of giants. On the contrary, in some cases, we cannot identify fingerprints of any of known scenarios. We show, however, that the four most Li-rich giants in our sample either have low-mass companions or have radial velocity variations at the level of ∼100 m s −1 , which strongly suggests that the presence of companions is an important factor in the Li-enrichment processes in giants.

Masses and luminosities for 342 stars from the PennState-Toruń Centre for Astronomy Planet Search

“…We also found that TYC 3930-01790-1 and three out of 16 stars with incomplete data in Zieliński et al (2012): TYC 0405-01700-1, TYC 3226-01083-1, TYC 3318-00020-1 are fast rotators with weak and variable CCF (see Fig. 1), which is in good agreement with the results of Adamów et al (2014) for the last three objects. All other stars presented in Zieliński et al (2012) show stable single CCF, which makes them either single or SB1.…”

Searching for Li-rich giants in a sample of 12 open clusters

“…127 hosts a brown dwarf of 19.8 M J at a distance of 2.4 AU with a period of 678 days (LM07). One can then speculate that a possible explanation for the enhanced Li observed in this star is the engulfment of a putative short-period planet that previously existed in the system as might be the case of other Li-rich planet hosts presented in Adamów et al (2012Adamów et al ( , 2014.…”

Far-infrared study of K giants in the solar neighborhood: Connection between Li enrichment and mass-loss

“…Also, several studies (Gonzalez et al 2009;Monaco et al 2011;Lebzelter et al 2012;Ruchti et al 2011;Martell & Shetrone 2013;Adamow et al 2014) report that some giants with large Li enhancement are occupied between the bump and tip of the RGB. It would be a worthwhile exercise to differentiate RGB stars from the early asymptotic giant branch (AGB) stars.…”

“…Thus, one ought to be cautious about associating Li-enhancement in K giants with the mass-loss events or vice versa. Also, assuming the possibility that planet engulfment enriches host-star Li abundance, hence IR excess (see Denissenkov & Herwig 2004;Carlberg et al 2010;Adamow et al 2014), and that the engulfment may happen anywhere along the RGB, one would expect Li enhancement across the RGB but not necessarily at the narrow bump luminosity. Absence of K giants with Li enhancement below and above the bump region casts shadow on the external origin scenario.…”

“…In addition to 15 new Lirich K giants, another 25 were included from the literature following the criterion suggested by Charbonnel & Balachandran (2000). The Li abundance data for the entire Li-rich sample was taken from Kumar et al (2011), Liu et al (2014, Adamow et al (2014), and references therein. Of the 25 Li-rich K giants taken from the literature 22 belong to the thin disk component, one to the thick disk component and one to the halo.…”