J. C. Sousa, M. S. Cunha

Abstract
High-resolution spectroscopic time series of rapidly oscillating Ap stars show evidence  for a co-existence of standing and running waves in their atmospheric layers. With the purpose of understanding these observations we have carried out a theoretical analysis of the pulsations in the outermost layers of these stars, starting from the simplest  possible model that still retains all important physical ingredients. In our analysis we   considered an isothermal atmosphere in a plane-parallel approximation. Moreover we assumed that in the region considered the magnetic pressure is much larger than the  gas pressure and, consequently, that the magnetoacoustic wave has decoupled into its  acoustic and magnetic components. Using the analytical solutions for the velocity  components appropriate to this model we estimate the velocity component parallel to  the line of sight averaged over the visible stellar disk. Fitting the latter to a function of  the form Acos(σt+phase), with σ the dimensionless oscillation frequency and t the dimensionless time, we derive the amplitude A and the phase for our model as  function of height in the atmosphere.

Proceedings of the Second HELAS International Conference
L. Gizon, M. Roth

Journal of Physics: Conference Series
Volume 118, Page 012074
2008 November

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