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Astron. Astrophys. 358, 1109-1121 (2000)

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Properties of the solar granulation obtained from the inversion of low spatial resolution spectra

C. Frutiger 1, S.K. Solanki 1,2, M. Fligge 1 and J.H.M.J. Bruls 3

1 Institute of Astronomy, ETH-Zentrum, 8092 Zürich, Switzerland
2 Max-Planck-Institut für Aeronomie, 37191 Katlenburg-Lindau, Germany
3 Kiepenheuer-Institut für Sonnenphysik, 79104 Freiburg, Germany

Received 16 December 1999 / Accepted 17 March 2000

Abstract

The spectra of cool stars are rich in information on elemental abundances, convection and non-thermal heating. Extracting this information is by no means straightforward, however. Here we demonstrate that an inversion technique may not only provide the stratification of the classical parameters describing a model atmosphere, but can also determine the properties of convection at the stellar surface. The inversion technique is applied to spectra of photospheric lines, one recorded at the quiet solar disk center, the other integrated over the whole disk. We find that a model based on a single plane-parallel atmosphere gives unsatisfactory fits to the spectral lines and suffers from considerable uncertainties in the derived temperature stratification. Also, the elemental abundances returned by the inversion are not particularly reliable. These problems are greatly reduced if two atmospheric components, corresponding to granular up- and downflows are allowed for. The best results are obtained if the line profiles and bisectors of a neutral and ionized species are fit and the results are constrained using a simple mass conservation scheme. We find that inversions based on two- and three-component models of disk-integrated spectra give similar results to inversions of disk-center observations, although with somewhat lower accuracy. This similarity is promising for future applications of line profile inversions to the study of late-type stars and in particular their convection.

Key words: line: profiles – radiative transfer – Sun: granulation – Sun: photosphere

Send offprint requests to: C. Frutiger (frutiger@astro.phys.ethz.ch)

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© European Southern Observatory (ESO) 2000

Online publication: June 20, 2000
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