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Height formation of bright points observed by IRIS in Mg II line wings during flux emergence

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    0469490 - ASÚ 2017 RIV FR eng J - Journal Article
    Grubecka, M. - Schmieder, B. - Berlicki, Arkadiusz - Heinzel, Petr - Dalmasse, K. - Mein, P.
    Height formation of bright points observed by IRIS in Mg II line wings during flux emergence.
    Astronomy & Astrophysics. Roč. 593, September (2016), A32/1-A32/17. ISSN 0004-6361. E-ISSN 1432-0746
    R&D Projects: GA ČR(CZ) GA16-18495S
    Grant - others:EC(XE) 606862
    Program: FP7
    Institutional support: RVO:67985815
    Keywords : Sun * chromosphere * activity
    OECD category: Astronomy (including astrophysics,space science)
    Impact factor: 5.014, year: 2016

    A flux emergence in the active region AR 111850 was observed on September 24, 2013 with the Interface Region Imaging Spectrograph (IRIS). Many bright points are associated with the new emerging flux and show enhancement brightening in the UV spectra. The aim of this work is to compute the altitude formation of the compact bright points (CBs) observed in Mg II lines in the context of searching Ellerman bombs (EBs). Within the two IRIS rasters, 74 CBs are detected in the far wings of the Mg II lines (at +/-1 angstrom and 3.5 angstrom). Around 10% of CBs have a signature in Si IV and CII. NLTE models with a hotspot located in the low atmosphere were found to fit a sample of Mg II profiles in CBs. The H alpha profiles computed with these Mg II CB models are consistent with typical EB profiles observed from ground based telescopes e.g. THEMIS. A 2D NLTE modelling of fibrils (canopy) demonstrates that the Mg II line centres can be significantly affected but not the peaks and the wings of Mg II lines. We conclude that the bright points observed in Mg II lines can be formed in an extended domain of altitudes in the photosphere and/or the chromosphere (400 to 750 km). Our results are consistent with the theory of heating by Joule dissipation in the atmosphere produced by magnetic field reconnection during flux emergence.

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