Line profile variations in rapidly oscillating Ap stars: resolution of the enigma

Abstract

We have carried out the first survey of the pulsational line profile variability in rapidly oscillating Ap (roAp) stars. We analysed high signal-to-noise time-series observations of ten sharp-lined roAp stars obtained with the high-resolution spectrographs attached to the VLT and CFHT telescopes. We investigated in detail the variations of Pr III, Nd II, Nd III and Tb III lines and discovered a prominent change of the profile variability pattern with height in the atmospheres of all studied roAp stars. In every investigated star profile variability of at least one rare-earth ion is characterized by unusual blue-to-red moving features - a behaviour inexplicable in the framework of the standard oblique pulsator model of slowly rotating roAp stars. Using analysis of the line profile moments and spectrum synthesis calculations, we demonstrate that unusual oscillations in spectral lines of roAp stars arise from the pulsational modulation of line widths. This variation occurs approximately in quadrature with the radial velocity changes, and its amplitude rapidly increases with height in stellar atmosphere. We propose that the line width modulation is a consequence of the periodic expansion and compression of turbulent layers in the upper atmospheres of roAp stars. Thus, the line profile changes observed in slowly rotating magnetic pulsators should be interpreted as a superposition of two types of variability: the usual time-dependent velocity field due to an oblique low-order pulsation mode and an additional line width modulation, synchronized with the changes of stellar radius. Our explanation of the line profile variations of roAp stars solves the long-standing observational puzzle and opens new possibilities for constraining geometric and physical properties of the stellar magnetoacoustic pulsations.

accepted by MNRAS; 22 pages, 17 figures, 5 tables

References in corpus (3)

• Rare-earth elements in the atmosphere of the magnetic chemically peculiar star HD 144897. New classification of the Nd III spectrum
• Improved pulsating models of magnetic Ap stars I: exploring different magnetic field configurations
• Pulsation in the atmosphere of the roAp star HD 24712. I. Spectroscopic observations and radial velocity measurements

Cited by in corpus (10)

• Rotation and pulsation in Ap stars: first light results from TESS sectors 1 and 2
• TESS Cycle 1 observations of roAp stars with 2-min cadence data
• Pulsations in the atmosphere of the rapidly oscillating Ap star 10 Aquilae
• MOST photometry and modeling of the rapidly oscillating (roAp) star gamma Equ
• The discovery of high-amplitude 10.9-minute oscillations in the cool magnetic Ap star HD 115226
• Discovery of very low amplitude 9-minute multiperiodic pulsations in the magnetic Ap star HD 75445
• Rapidly-oscillating {\it TESS} A--F main sequence stars: are the roAp stars a distinct class?
• The Paschen-Back effect in the Li I 6708 A line and the presence of lithium in cool magnetic Ap stars
• Using Doppler Imaging to model stellar activity and search for planets around Sun-like stars
• SALT HRS capabilities for time resolved pulsation analysis: a test with the roAp star $\alpha$ Circini