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Numerical Simulation of Granular Convection: Effects on Photospheric Spectral Line Profiles

Published online by Cambridge University Press:  12 April 2016

Åke Nordlund
Åke Nordlund*
Affiliation:
Nordita, Blegdamsvej 17, Dk-2100, København Ø, Denmark

Abstract

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The results of numerical simulations of the solar granulation are used to investigate the effects on photospheric apectral lines of the correlated velocity and temperature fluctuations of the convective granular motions. It is verified that the granular velocity field is the main cause for the observed broadening and strengthening of photospheric spectral lines relative to values expected from pure thermal and pressure broadening. These effects are normally referred to as being due to “macro-turbulence” and “micro-turbulence”, respectively. It is also shown that the correlated temperature and velocity fluctuations produce a “convective blue shift” in agreement with the observed blue shift of photospheric spectral lines. Reasons are given for the characteristic shapes of spectral line bisectors, and the dependence of these shapes on line strength, excitation potential, and center to limb distance are discussed.

Type
3. Conceptualizations of Turbulence
Information
International Astronomical Union Colloquium , Volume 51: Stellar Turbulence , 1980 , pp. 213 - 224
Copyright
Copyright © Springer-Verlag 1980

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