Discovery of the longest-period rapidly oscillating Ap star HD177765

TL;DR

This paper reports the discovery of HD177765, a long-period rapidly oscillating Ap star with unique pulsation characteristics, providing insights into stellar evolution and chemical peculiarities in Ap stars.

Contribution

It is the first detection of a roAp star with a pulsation period exceeding 20 minutes, expanding understanding of pulsation properties in chemically peculiar stars.

Findings

Pulsation period of 23.6 minutes exceeds previous records.

Largest amplitudes observed in Eu III, Ce III, and Halpha core.

Indicates advanced evolutionary stage and chemical peculiarities.

Abstract

We present the discovery of a long-period, rapidly oscillating Ap star, HD177765. Using high-resolution time-series observations obtained with UVES at the ESO VLT telescope, we found radial velocity variations with amplitudes 7-150 m/s and a period of 23.6 min, exceeding that of any previously known roAp star. The largest pulsation amplitudes are observed for Eu III, Ce III and for the narrow core of Halpha. We derived the atmospheric parameters and chemical composition of HD177765, showing this star to be similar to other long-period roAp stars. Comparison with theoretical pulsational models indicates an advanced evolutionary state for HD177765. Abundance analyses of this and other roAp stars suggest a systematic variation with age of the rare-earth line anomalies seen in cool Ap stars.