A 3-D study of the photosphere of HD99563: I. Pulsation analysis

TL;DR

This study uses high-speed spectroscopy to analyze pulsation behaviors and surface element distribution in the star HD99563, revealing magnetic and pulsation interactions that support theories of roAp star excitation.

Contribution

It provides the first observation of H-alpha abundance spots caused by He settling and demonstrates aspect-dependent pulsation features in HD99563, advancing understanding of magnetic and pulsation interactions in roAp stars.

Findings

Detection of 1.6 km/s rotational variation in H-alpha radial velocities.

First observation of H-alpha abundance spots due to He settling.

Aspect dependence of blue-to-red wave variations in Nd iii spots.

Abstract

We have used high-speed spectroscopy of the rapidly oscillating Ap (roAp) star HD99563 to study the pulsation amplitude and phase behaviour of elements in its stratified atmosphere over one 2.91-d rotation cycle. We identify spectral features related to patches in the surface distribution of chemical elements and study the pulsation amplitudes and phases as the patches move across the stellar disk. The variations are consistent with a distorted nonradial dipole pulsation mode. We measure a 1.6 km/s rotational variation in the mean radial velocities of H-alpha and argue that this is the first observation of H-alpha abundance spots caused by He settling through suppression of convection by the magnetic field on an oblique rotator, in support of a prime theory for the excitation mechanism of roAp star pulsation. We demonstrate that HD99563 is the second roAp star to show aspect dependence of blue-to-red running wave line profile variations in Nd iii spots.