Semi-empirical model atmospheres for the chromosphere of the sunspot penumbra and umbral flashes

Abstract

Context. The solar chromosphere and the lower transition region is believed to play a crucial role in the heating of the solar corona. Models that describe the chromosphere (and the lower transition region), accounting for its highly dynamic and structured character are, so far, found to be lacking. This is partly due to the breakdown of complete frequency redistribution in the chromospheric layers and also because of the difficulty in obtaining complete sets of observations that adequately constrain the solar atmosphere at all relevant heights. Aims. We aim to obtain semi-empirical model atmospheres that reproduce the features of the Mg II h&k line profiles that sample the middle chromosphere with focus on a sunspot. Methods. We use spectropolarimetric observations of the Ca II 8542 A spectra obtained with the Swedish 1-m Solar Telescope (SST) and use NICOLE inversions to obtain semi-empirical model atmospheres for different features in and around a sunspot. These are used to synthesize Mg II h&k spectra using RH1.5D code, which we compare with observations taken with the Interface Region Imaging Spectrograph (IRIS). Results. Comparison of the synthetic profiles with IRIS observations reveals that there are several areas, especially in the penumbra of the sunspot, where most of the observed Mg II h&k profiles are very well reproduced. In addition, we find that supersonic hot downflows, present in our collection of models in the umbra, lead to synthetic profiles that agree well with the IRIS Mg II h&k profiles, with the exception of the line core. Conclusions. We put forward and make available four semi-empirical model atmospheres. Two for the penumbra, reflecting the range of temperatures obtained for the chromosphere, one for umbral flashes, and a model representative of the quiet surroundings of a sunspot. These are available in electronic as well as in table formats.

Accepted for publications at A&A 20 May 2019

References in corpus (14)

• CRISP Spectropolarimetric Imaging of Penumbral Fine Structure
• CRISPRED: A data pipeline for the CRISP imaging spectropolarimeter
• An Open Source, Massively Parallel Code for Non-LTE Synthesis and Inversion of Spectral Lines and Zeeman-induced Stokes Profiles
• Advanced Forward Modeling and Inversion of Stokes Profiles Resulting from the Joint Action of the Hanle and Zeeman Effects
• Inversion of the radiative transfer equation for polarized light
• RH 1.5D: a massively parallel code for multi-level radiative transfer with partial frequency redistribution and Zeeman polarisation
• Non-LTE inversions of the Mg II h&k and UV triplet lines
• 3D Temperature Mapping of Solar Photospheric Fine Structure Using Ca II H Filtergrams
• Radiative diagnostics in the solar photosphere and chromosphere
• Detection of supersonic downflows and associated heating events in the transition region above sunspots
• Synthetic observations of wave propagation in a sunspot umbra
• A Hot Downflowing Model Atmosphere For Umbral Flashes And The Physical Properties Of Their Dark Fibrils
• The solar chromosphere at millimetre and ultraviolet wavelengths. I. Radiation temperatures and a detailed comparison
• The formation of small-scale umbral brightenings in sunspot atmospheres

Cited by in corpus (1)

• High-resolution observations of the solar photosphere, chromosphere and transition region. A database of coordinated IRIS and SST observations