NLTE modelling of the flaring atmosphere above sunspot

¹ Observatoire de Paris, Section de Meudon, LESIA, 92195 Meudon Principal Cedex, France
² Astronomical Institute, Wrocław University, 51-622 Wrocław, Poland e-mail: berlicki@astro.uni.wroc.pl
³ Astronomical Institute, Academy of Sciences of the Czech Republic, 25165 Ondřejov, Czech Republic
⁴ Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, PR China

Received: 11 April 2008
Accepted: 9 July 2008

Abstract

Aims. We performed an analysis of the solar flaring atmosphere above sunspots. During the flare on October 20, 2003 many flaring structures were observed projected onto the sunspots. We analysed the Hα and Ca II line profiles emitted by the ribbons partially overlapping the sunspots. In the penumbra, the line intensity in the far wings is lower than in a typical quiet Sun profile but the core emission of Hα and Ca II lines is typical for flares. We tried to find the structure of the flare observed above the sunspot penumbra using the observations of these chromospheric line profiles.

Methods. NLTE radiative transfer techniques allowed us to model the atmosphere of flaring structures and fit both the synthetic Hα and Ca II line profiles to the observed ones. We have derived semiempirical models of the flaring structure observed above sunspots.

Results. Our analysis shows that the flare emission observed within the sunspot penumbra comes from geometrically thin loop-like structures (cool flare loops) located above the fibrils of the penumbra. The structure of the penumbra located below the flare is almost not affected by the flare i.e. the flare emission in Hα and Ca II comes not from the upper chromosphere but from the structures that are higher in the corona. Therefore, a two-component modelling is necessary to reproduce the flare emission above the sunspot penumbra detected in our observations.