Astronomy and Astrophysics – Astrophysics
Scientific paper
2004-09-26
Astrophys.J. 615 (2004) L149-L152
Astronomy and Astrophysics
Astrophysics
accepted by ApJ Letters
Scientific paper
10.1086/426117
Many types of stars show periodic variations of radius and brightness, which are commonly referred to as `stellar pulsations'. Observed pulsational characteristics are determined by fundamental stellar parameters. Consequently, investigations of stellar pulsations provide a unique opportunity to verify and refine our understanding of the evolution and internal structure of stars. However, a key boundary condition for this analysis -- precise information about the geometry of pulsations in the outer stellar envelopes -- has been notoriously difficult to secure. Here we demonstrate that it is possible to solve this problem by constructing an `image' of the pulsation velocity field from time series observations of stellar spectra. This technique is applied to study the geometry of nonradial pulsations in a prototype magnetic oscillating (roAp) star HR 3831. Our velocity map directly demonstrates an alignment of pulsations with the axis of the global magnetic field and reveals a significant magnetically induced distortion of pulsations. This observation constitutes a long-sought solution of the problem of the pulsation geometry of roAp stars and enables very stringent tests of the recent theories of stellar magneto-acoustic oscillations.
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