On producers of cosmic organic compounds: exploring the boron abundance in lithium-rich K giant stars

TL;DR

This study investigates boron abundance in lithium-rich giant stars using UV spectra from the Hubble telescope to test planetary engulfment hypotheses and explore stellar activity and organic compounds.

Contribution

First UV spectroscopic analysis of boron in lithium-rich giants, providing new insights into stellar processes and challenging planet engulfment explanations.

Findings

Boron abundances are not elevated, suggesting planet engulfment is unlikely.

Stars with high lithium show strong chromospheric activity.

UV results complement previous mid-IR findings of organic material emissions.

Abstract

The element boron belongs, together with lithium and beryllium, to a known trio of important elements for the study of evolutionary processes in low mass stars. Because B is the least fragile of this trio to be destroyed in the stellar interiors, it can be used to test if the Li enrichment is of planetary origin. Here, for the first time, boron lines are examined in the UV for four giants with different degrees of large Li enrichment by means of observations with the Hubble telescope. Two main results are found in our study. One is that to first approximation B abundances appear not to be in excess, invalidating the planet engulfment mechanism. The second one is that the two stars with very large Li abundances present emission lines indicating that quite strong active chromospheres are acting in these very Li-rich giants. These new results obtained from the UV complement our recent studies in the mid-IR (de la Reza et al. 2015) where strong emission-line features of organic material were found in the spectra of some Li-rich stars.