Tracking Advanced Planetary Systems (TAPAS) with HARPS-N

II. Super Li-rich giant HD 107028^{⋆,⋆⋆,⋆⋆⋆}

¹ McDonald Observatory and Department of Astronomy, University of Texas at Austin, 2515 Speedway, Stop C1402, Austin, Texas, 78712-1206, USA
e-mail: madamow@astro.as.utexas.edu
² Toruń Centre for Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100, 87-100 Toruń, Poland
e-mail: Andrzej.Niedzielski@umk.pl
³ Departamento de Física Teórica, Universidad Autónoma de Madrid, Cantoblanco 28049 Madrid, Spain
e-mail: Eva.Villaver@uam.es
⁴ Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802, USA
e-mail: alex@astro.psu.edu
⁵ Center for Exoplanets and Habitable Worlds, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802, USA
⁶ National Center for Supercomputing Applications, University of Illinois Urbana-Champaign, 1205 W Clark St, MC-257, Urbana, IL 61801, USA
⁷ Instituto de Astrofísica de Canarias, C/Vía Láctea, s/n, 38205 La Laguna, Tenerife, Spain
⁸ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain

Received: 22 May 2015
Accepted: 9 July 2015

Abstract

Context. Lithium-rich giant stars are rare objects. For some of them, Li enrichment exceeds the abundance of this element found in solar system meteorites, suggesting that these stars have gone through a Li enhancement process.

Aims. We identified a Li-rich giant HD 107028 with A(Li) > 3.3 in a sample of evolved stars observed within the PennState Toruń Planet Search. In this work we study different enhancement scenarios and we try to identify the one responsible for Li enrichment in HD 107028.

Methods. We collected high-resolution spectra with three different instruments, covering different spectral ranges. We determined stellar parameters and abundances of selected elements with both equivalent width measurements and analysis, and spectral synthesis. We also collected multi-epoch high-precision radial velocities in an attempt to detect a companion.

Results. Collected data show that HD 107028 is a star at the base of the red giant branch (RGB). Except for high Li abundance, we have not identified any other anomalies in its chemical composition, and there is no indication of a low-mass or stellar companion. We exclude Li production at the luminosity function bump on the RGB as the effective temperature and luminosity suggest that the evolutionary state is much earlier than the RGB bump. We also cannot confirm the Li enhancement by contamination as we do not observe any anomalies that are associated with this scenario.

Conclusions. After evaluating various scenarios of Li enhancement we conclude that the Li-overabundance of HD 107028 originates from main-sequence evolution, and may be caused by diffusion processes.