The 10830 He I Absorption Line Among Metal-Poor Subdwarfs

TL;DR

This study presents near-infrared spectra of 23 metal-poor stars, revealing that most exhibit He I 10830 absorption lines indicative of chromospheres, with properties similar to solar metallicity stars of low activity.

Contribution

First systematic investigation of He I 10830 line in metal-poor stars, showing chromospheric activity across a range of metallicities and stellar types.

Findings

Most stars show He I absorption indicating chromospheres.

Equivalent widths are generally less than 70 mA, similar to low-activity solar stars.

No correlation between He I strength and metallicity or color.

Abstract

Spectra of the He I 10830 line have been obtained for 23 metal-poor stars, the majority of which are dwarfs ranging in metallicity from [Fe/H] = -2.1 to -0.8. The data were acquired with the NIRSPEC spectrograph on the Keck 2 telescope. Most of these subdwarfs and dwarfs are found to exhibit a He I absorption line indicative of the presence of chromospheres. The equivalent width of the 10830 absorption profile is generally less than 70 mA, and covers a range similar to that found in solar metallicity stars of low activity. Among the subdwarfs the He I equivalent width does not correlate with either [Fe/H] metallicity or (B-V) color. Some evidence for asymmetric profiles is found among metal-poor dwarfs, but not the high-speed blue-shifted absorption displayed by some metal-poor red giants.