Departures from LTE for neutral Li in late-type stars

TL;DR

This study performs detailed non-LTE calculations for lithium in late-type stars, considering advanced collision data, to improve the accuracy of lithium abundance measurements across various stellar parameters.

Contribution

It introduces new quantum mechanical collisional data and provides comprehensive non-LTE correction grids for lithium lines in late-type stars.

Findings

Non-LTE effects vary with stellar parameters and lithium abundance.

Corrections for the 670.7nm line can be significant and vary in size and sign.

New collisional data significantly influence abundance correction calculations.

Abstract

We perform non-LTE calculations of lithium in late-type stars for a wide range of stellar parameters, including quantum mechanical cross-sections for collisions with neutral hydrogen and the negative hydrogen ion. Non-LTE abundance corrections for the lithium resonance line at 670.7nm and the subordinate line at 610.3nm, are calculated using 1D MARCS model atmospheres spanning a grid Teff=[4000,8000]K, log(g)=[1.0,5.0], and [Fe/H]=[0.0,-3.0], for lithium abundances in the range A(Li)=[-0.3,4.2]. The competing effects of ultraviolet over-ionization and photon losses in the resonance line govern the behaviour of the non-LTE effects with stellar parameters and lithium abundance. The size and sign of the non-LTE abundance corrections vary significantly over the grid for the 670.7nm line, but are typically positive and below 0.15dex for the 610.3nm, line. The new collisional data play a significant role in determining the abundance corrections.