Absorption Lines in the 0.91-1.33 $\mu$m Spectra of Red Giants for Measuring Abundances of Mg, Si, Ca, Ti, Cr, and Ni

TL;DR

This study identifies and measures absorption lines of key elements in the near-infrared spectra of red giants to improve stellar abundance analysis, comparing line lists and assessing measurement accuracy.

Contribution

It provides a new line list for six elements in the 0.91-1.33 μm range and demonstrates their use in high-resolution spectra for abundance determination.

Findings

Reasonable agreement with literature abundances within 0.2 dex.

Systematic differences of 0.1-0.2 dex between line lists.

Highlighting the importance of microturbulence estimation for precision.

Abstract

Red giants show a large number of absorption lines in both optical and near-infrared wavelengths. Still, the characteristics of the lines in different wave passbands are not necessarily the same. We searched for lines of Mg I, Si I, Ca I, Ti I, Cr I, and Ni I in the z', Y, and J bands (0.91-1.33 $\mu$m), that are useful for precise abundance analyses, from two different compilations of lines, namely, the third release of Vienna Atomic Line Database (VALD3) and the catalog published by Melendez & Barbuy in 1999 (MB99). We selected sufficiently strong lines that are not severely blended and ended up with 191 lines (165 and 141 lines from VALD3 and MB99, respectively), in total, for the six elements. Combining our line lists with high-resolution (R = 28,000) and high signal-to-noise (higher than 500) spectra taken with the WINERED spectrograph, we measured the abundances of the six elements in addition to Fe I of two prototype red giants, i.e., Arcturus and mu Leo. The resultant abundances show reasonable agreements with literature values within $\sim$0.2 dex, indicating that the available oscillator strengths are acceptable, although the abundances based on the two line lists show systematic differences by 0.1-0.2 dex. Furthermore, to improve the precision, solid estimation of the microturbulence (or the microturbulences if they are different for different elements) is necessary as far as the classical hydrostatic atmosphere models are used for the analysis.