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Astron. Astrophys. 358, 575-582 (2000)


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The contribution of the micro-turbulent velocity on the modelling of chromospheric lines in late type dwarfs *

D. Jevremovi 1,2, J.G. Doyle 1 and C.I. Short 3

1 Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland (djc,jgd@star.arm.ac.uk)
2 Belgrade Observatory, Volgina 7, 11160 Belgrade 74, Yugoslavia
3 Department of Physics and Astronomy, University of Georgia, Athens, GA 30602-2451, USA

Received 29 October 1999 / Accepted 11 April 2000

Abstract

We discuss the influence of the non-thermal velocity (micro-turbulence) on the formation of chromospheric lines in the atmospheres of late type dwarfs. A review of previous work shows a variety of different approaches to the problem leading to different atmospheric structures and consequently different computed line profiles. In that light, we re-examine the formation of the Hydrogen Balmer lines and Na I D lines using twelve different distributions of the micro-turbulent velocity throughout the atmosphere. Our results show a wide range of possible line shapes. Using the analogy with the solar case and the latest results of the non-thermal component widths as derived from instruments on-board SOHO we model H[FORMULA] and the Na I D lines in an active dMe star Gl 616.2.

Key words: line: formation – line: profiles – turbulence – stars: activity – stars: chromospheres – stars: late-type

* Based in part on observations made at Observatoire de Haute Provence (CNRS), France and SOHO

Send offprint requests to: D. Jevremovi

© European Southern Observatory (ESO) 2000

Online publication: June 8, 2000

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