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Astron. Astrophys. 340, 203-215 (1998)

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Energy and momentum deposition in coronal holes

Solar coronal hole simulations compared with interpretations of Yohkoh SXT observations

K. Tziotziou 1, P.C.H. Martens 2 and A.G. Hearn 1

1 Sterrekundig Instituut, Postbus 80000, 3508 TA Utrecht, The Netherlands (A.G.Hearn@astro.uu.nl)
2 SOHO Project, ESA Space Science Department at Goddard Space Flight Center, Code 682.3, Greenbelt, MD 20771, USA

Received 5 January 1998 / Accepted 27 July 1998

Abstract

A grid of 74 coronal models with parameterized heating distribution, representing a wide range of physical parameters, has been calculated. We find that three of these models reproduce the recent observations made by Hara et al. (1994) with the soft X-ray telescope aboard the Japanese satellite Yohkoh , which indicate a temperature of [FORMULA] with an emission measure of [FORMULA] to [FORMULA], while other solutions reproduce the more standard Yohkoh and Skylab observations, which have a temperature of about [FORMULA]

The best fit for the coronal temperature and emission measure gives a velocity at the Earth's orbit of only [FORMULA]. A model including acceleration by Alfvén waves gives a final velocity of [FORMULA] which is in agreement with the observations. The mechanical heating flux at the transition region is [FORMULA] with a weighted average dissipation scale length of [FORMULA]. The flux of Alfvén waves is [FORMULA].

In our models the velocity of the solar wind from coronal holes is completely determined by the Alfvén wave acceleration, in contrast to previous models in which the Alfvén wave acceleration increased the velocity of the purely thermal model only by a factor 2.

Observations of the non thermal broadening of the coronal red and green lines are consistent with this model.

Key words: hydrodynamics – methods: numerical – stars: coronae – stars: mass loss

Send offprint requests to: A.G. Hearn

This article contains no SIMBAD objects.

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© European Southern Observatory (ESO) 1998

Online publication: November 3, 1998
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