Chemical abundances in cool metal rich disk dwarf stars

TL;DR

This study refines the chemical abundance analysis of cool, metal-rich dwarf stars, demonstrating that previous anomalies were due to analysis methods, and provides more accurate abundance measurements using spectrum synthesis.

Contribution

It introduces a spectrum synthesis method with strict excitation equilibrium to accurately determine chemical abundances in metal-rich cool dwarf stars, resolving prior abundance anomalies.

Findings

Metal-rich K dwarf stars do not show anomalous abundances.

The new method yields consistent abundance patterns across different stars.

Ionization and excitation equilibrium are achieved after temperature corrections.

Abstract

The present study of spectra of twelve metal-rich cool dwarf stars, carefully selected in order to cover a range of temperatures (~4400 - 6000 K), is a follow up on Feltzing & Gustafsson (1998, A&AS 129, 237) with the aim to understand the apparent over-ionization and anomalous elemental abundances found by them for the K dwarf stars in their sample. Our method of analysis employs synthetic spectra of the full spectrum both to constrain the continuum level and to derive abundances. It is shown that by using this method and imposing a strict excitation equilibrium (possible to do because of the care in selection of observed Fe I lines) we are able to show that metal-rich K dwarf stars do not show anomalous stellar abundances, as indicated in Feltzing & Gustafsson (1998), and can, with reasonable efforts, be analyzed in order to increase the number of metal-rich stars with useful chemical abundances. With abundance analysis by means of spectrum synthesis and assuming Local Thermodynamic Equilibrium (LTE) the abundances of Na, Si, Ca, Sc, Ti, V, Cr, Fe, Co, Ni, and Nd have been derived. Also ionization balance is satisfied for Fe and Cr after correcting the stellar effective temperatures such that both ionization and excitation equilibrium were satisfied. In addition, spectra from five cool dwarf stars of the Feltzing & Gustafsson (1998) sample have been analyzed with the methods used in this work. They show essentially the same abundance patterns as the new stars in this sample.