Pulsational line profile variation of the roAp star HR 3831

Abstract

We report the first comprehensive investigation of the line profile variation caused by non-radial pulsation in a magnetic oscillating chemically peculiar star. Spectrum variation of the well-known roAp star HR 3831 is detected using very high-resolution high signal-to-noise spectroscopic time-series observations and are followed through the whole rotation cycle of the star. We confirm outstanding diversity of pulsational behaviour of different lines in the HR 3831 spectrum and attribute this phenomenon to an interplay between extreme vertical chemical inhomogeneity of the HR 3831 atmosphere and a running pulsation wave, propagating towards the upper photospheric layers with increasing amplitude. Rapid profile variation of the NdIII 6145 A line is characterized by measuring changes of its equivalent width and the first three moments. We demonstrate that rotational modulation of the radial velocity oscillations cannot be fully explained by an oblique axisymmetric dipole (ell=1, m=0) mode, implied by the classical oblique pulsator model of roAp stars. Pulsational variation of the higher moments reveal substantial contribution of the high-order (ell=3) spherical harmonics which appear due to distortion of pulsations in HR 3831 by the global magnetic field. We interpret observations with a novel numerical model of the pulsational variation and rotational modulation of the line profile moments in roAp stars. The comparison between observed and computed amplitudes and phases of the radial velocity and line width variation is used to establish parameters of the oblique pulsator model of HR 3831. Furthermore, definite detection of pulsational variation in lines of light and iron-peak elements enables the first 3-D mapping of pulsations in non-radially oscillating star.

21 pages, 11 figures; accepted by A&A

References in corpus (3)

• Radial Velocity Variations in Pulsating Ap Stars. II. 33 Librae
• Indirect imaging of nonradial pulsations in a rapidly oscillating Ap star
• Variation of the line profile moments for stars pulsating in distorted oblique non-radial modes

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