TheGaia-ESO Survey: properties of newly discovered Li-rich giants

Abstract

Aims. We report 20 new lithium-rich giants discovered within the Gaia-ESO Survey, including the first Li-rich giant with an evolutionary stage confirmed by CoRoT (Convection, Rotation and planetary Transits) data. We present a detailed overview of the properties of these 20 stars. Methods. Atmospheric parameters and abundances were derived in model atmosphere analyses using medium-resolution GIRAFFE or high-resolution UVES (Ultraviolet and Visual Echelle Spectrograph) spectra. These results are part of the fifth internal data release of the Gaia-ESO Survey. The Li abundances were corrected for non-local thermodynamical equilibrium effects. Other stellar properties were investigated for additional peculiarities (the core of strong lines for signs of magnetic activity, infrared magnitudes, rotational velocities, chemical abundances, and Galactic velocities). We used Gaia DR2 parallaxes to estimate distances and luminosities.Results. The giants have A(Li) > 2.2 dex. The majority of them (14 of 20 stars) are in the CoRoT fields. Four giants are located in the field of three open clusters, but are not members. Two giants were observed in fields towards the Galactic bulge, but likely lie in the inner disc. One of the bulge field giants is super Li-rich with A(Li) = 4.0 dex. Conclusions. We identified one giant with infrared excess at 22µm. Two other giants, with large v sin i, might be Li-rich because of planet engulfment. Another giant is found to be barium enhanced and thus could have accreted material from a former asymptotic giant branch companion. Otherwise, in addition to the Li enrichment, the evolutionary stages are the only other connection between these new Li-rich giants. The CoRoT data confirm that one Li-rich giant is at the core-He burning stage. The other giants are concentrated in close proximity to the red giant branch luminosity bump, the core-He burning stages, or the early-asymptotic giant branch. This is very clear from the Gaia-based luminosities of the Li-rich giants. This is also seen when the CoRoT Li-rich giants are compared to a larger sample of 2252 giants observed in the CoRoT fields by the Gaia-ESO Survey, which are distributed throughout the red giant branch in the T eff -log g diagram. These observations show that the evolutionary stage is a major factor for the Li enrichment in giants. Other processes, such as planet accretion, contribute at a smaller scale.

Lithium in red giant stars: Constraining non-standard mixing with large surveys in the Gaia era

“…Some studies use Hipparcos or Gaia data to determine the evolutionary status of field LiRG and show that these objects tend to accumulate close to the RGB bump, the clump, and the early-AGB (e.g. Charbonnel & Balachandran 2000;Kumar et al 2011;Smiljanic et al 2018;Deepak & Reddy 2019), which is in agreement with open cluster studies (e.g. Delgado Mena et al 2016).…”

“…Smith & Lambert 1989;Forestini & Charbonnel 1997;Domínguez et al 2004). Since the discovery of the first LiRG (Wallerstein & Sneden 1982), several surveys have reported the existence of such objects which account for ∼ 1 -2 % of the studied populations (Brown et al 1989;Charbonnel & Balachandran 2000;Reddy & Lambert 2005;Lèbre et al 2006;Gonzalez et al 2009;Kumar et al 2011;Monaco et al 2011;Lyubimkov et al 2012;Casey et al 2016;Smiljanic et al 2018;Yan et al 2018;Singh et al 2019;Deepak & Reddy 2019). Some studies use Hipparcos or Gaia data to determine the evolutionary status of field LiRG and show that these objects tend to accumulate close to the RGB bump, the clump, and the early-AGB (e.g.…”

“…In particular, the AMBRE and GALAH surveys have yielded public catalogues with Li abundances for, respectively, ∼ 7 300 and 342 000 stars covering a large range in metallicity and evolutionary status (Guiglion et al 2016;Buder et al 2018;Deepak & Reddy 2019). A couple of studies have also searched for Lirich stars from the Gaia-ESO survey (Casey et al 2016(Casey et al , 2019Smiljanic et al 2018) and the LAMOST survey (Cui et al 2012;Singh et al 2019).…”

Concerning the Li-rich status of KIC 9821622: a Kepler field RGB star reported as a Li-rich giant

“…This is quite significant as this survey is based on large unbiased data set drawn from Kepler (Borucki et al 2010) and LAMOST (Cui et al 2012) catalogs. This study reconfirms earlier serendipitous discoveries of five Li-rich giants, all of them have been classified as red clump giants based on asteroseismic data (Silva Aguirre et al 2014;Carlberg et al 2015;Bharat Kumar et al 2018;Smiljanic et al 2018). The mounting evidence that Li-rich phenomenon is probably associated only with He-core burning giants, post-He-flash, has been further strengthened by a recent large survey of Li-rich giants among GALAH (De Silva et al 2015) and GAIA (Gaia Collaboration et al 2018) catalogs by Deepak & Reddy (2019), in which they showed a vast majority of Li-rich giants belong to red clump region.…”

Abundance analyses of Li-enriched and normal giants in the GALAH survey

“…Our sample of Li-rich giants is not s-process enriched. The Gaia-ESO survey of Li-rich giants (Casey et al 2016;Smiljanic et al 2018) has provided information on the compositions of a few giants indicating essentially normal compositions relative to normal giants.…”