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Issue A&A
Volume 372, Number 1, June II 2001
Page(s) L13 - L16
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20010540



A&A 372, L13-L16 (2001)
DOI: 10.1051/0004-6361:20010540

Radiative properties of magnetic elements

I. Why are $\vec G$-band bright points bright?
O. Steiner1, P. H. Hauschildt2 and J. Bruls1

1  Kiepenheuer-Institut für Sonnenphysik, Schöneckstrasse 6, 79104 Freiburg, Germany
2  The University of Georgia, Dept. of Physics & Astronomy, Athens, GA 30602-2451, USA

(Received 1 February 2001 / Accepted 11 April 2001)

Abstract
Photospheric magnetic elements are most conspicuously visible in high-resolution G-band filtergrams. We show that their enhanced contrast in the G-band is due to a reduction of the CH abundance by dissociation in the deep photospheric layers of the flux tube, where it is hotter than in the surrounding atmosphere. As a consequence, the CH-lines weaken, allowing more of the continuum to "shine" through the forest of G-band CH-lines. We suggest that other molecular bands or atomic lines may exhibit a similar behaviour.


Key words: Sun: photosphere -- Sun: magnetic fields -- Sun: faculae, plages -- solar irradiance variability -- G-band

Offprint request: O. Steiner, steiner@kis.uni-freiburg.de




© ESO 2001


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