Line Broadening in Field Metal-poor Red Giant and Red Horizontal Branch Stars

TL;DR

This study measures radial velocities and line broadening in metal-poor red giant and horizontal branch stars, revealing binary systems, velocity jitter, and broadening phenomena linked to stellar luminosity.

Contribution

It provides new radial velocity data, identifies binary systems, and analyzes line broadening in metal-poor evolved stars, expanding understanding of their spectral characteristics.

Findings

Identification of new spectroscopic binary HD 4306

Detection of velocity jitter in luminous stars

Significant line broadening in the most luminous giants

Abstract

We report 349 radial velocities for 45 metal-poor field red giant and red horizontal branch stars. We have have identified one new spectroscopic binary, HD 4306, and one possible such system, HD 184711. We also report 57 radial velocities for 11 of the 91 stars reported on previously by Carney et al. (2003). As was found in the previous study, radial velocity "jitter" is present in many of the most luminous stars. Excluding stars showing spectroscopic binary orbital motion, all 7 of the red giants with M(V) <= -2.0 display jitter, as well as 3 of the 14 stars with -2.0 <= M(V) <= -1.4. We have also measured line broadening in all of the new spectra, using synthetic spectra as templates. The most luminous red giants show significant line broadening, as do many of the red horizontal branch stars, and we discuss briefly possible causes.