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Astron. Astrophys. 325, 709-713

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Chromospheric velocity fields in Orionis (M2 Iab)
generated by stochastic shocks

M. Cuntz1,2

1Center for Space Plasma and Aeronomic Research (CSPAR), EB 136M, University of Alabama in Huntsville, Huntsville, AL 35899, USA
2Institut für Theoretische Astrophysik der Universität Heidelberg, Tiergartenstr. 15, D-69121 Heidelberg, Germany

Received 24 February 1997 / Accepted 25 March 1997


I present results from recent ab-initio models for the formation and time-dependent behavior of outer atmospheric flows in FORMULA Ori (M2 Iab) produced by stochastic shock waves. Stochastic shocks are a natural consequence of acoustic energy generation due to stellar convection. The wave models show distinct episodes of momentum and energy deposition produced by strong shocks generated by merging of shocks in the stochastic wave field. It is found that sub- and supersonic inflows and outflows are generated at different atmospheric heights as function of the wave parameters adopted. The flow velocities given by the models encompass the velocity range revealed by the Fe II emission line components given by recent GHRS data (Carpenter & Robinson 1997). This result is evidence that nonmagnetic wave modes are relevant for the heating and dynamics of the outer atmosphere of FORMULA Ori and possibly other M-type supergiants as well, although it does not preclude the possibility that magnetic heating may be equally or more important.

Key words: hydrodynamics - shock waves - waves - stars: chromospheres - stars: individual: FORMULA Ori - stars: supergiants

© European Southern Observatory (ESO) 1997

Online publication: September 9, 1997
Last change: April 28, 1998