Radial velocity measurements of the pulsating zirconium star: LS IV -14 116

TL;DR

This study reports radial velocity measurements of the pulsating zirconium-rich hot subdwarf LS IV -14 116, revealing non-radial pulsations and differential photospheric pulsation behavior despite unusual surface properties.

Contribution

It provides the first evidence of radial velocity variability linked to pulsations in LS IV -14 116, highlighting non-radial g-mode pulsations in a chemically stratified star.

Findings

Detected radial velocity variations with amplitudes over 5 km/s.

Found correlation between line strength and pulsation amplitude.

Concluded pulsations are non-radial due to light-to-velocity amplitude ratio.

Abstract

The helium-rich hot subdwarf LS IV -14 116 shows remarkably high surface abundances of zirconium, yttrium, strontium, and germanium, indicative of strong chemical stratification in the photosphere. It also shows photometric behaviour indicative of non-radial g-mode pulsations, despite having surface properties inconsistent with any known pulsational instability zone. We have conducted a search for radial velocity variability. This has demonstrated that at least one photometric period is observable in several absorption lines as a radial velocity variation with a semi-amplitude in excess of 5 km s$^{-1}$. A correlation between line strength and pulsation amplitude provides evidence that the photosphere pulsates differentially. The ratio of light to velocity amplitude is too small to permit the largest amplitude oscillation to be radial.