Non-LTE modelling of a filament in state of activation observed in Hα by the IBIS interferometer

by P. Schwartz (speaker), S. Gunár, P. Heinzel, J. Jenkins, D. Long

Hosted by Astronomical Institute, Slovak Academy of Sciences on October 18, 2018


We present development, current state and plans for future improvements of our non-LTE 2D flux-tube model. The model is used for simulations of spectroscopic observations in the Hα line of small-scale filaments in active regions, arc filaments and filaments in state of activation. We assume that filaments of these types are composed of flux-tubes located in the transition region and/or corona and relatively cool plasma can flow along these flux-tubes with various velocities. In the current state of the model, the flux-tube system is approximated by a 2D horizontal slab where its finite dimensions form its cross section and the infinite dimension is directed along filament parallel to the solar surface. The isothermal and isobaric slab is irradiated from the bottom and sides and the non-LTE radiative transfer in the 2D geometry is solved using the MALI numerical technique. The orientation of plasma flows in the slab is defined by the azimuth and inclination angles. Diverse unresolved plasma motions in individual flux-tubes are included via micro-turbulence velocity as one of input parameters of the model. At present, we are using the model for the Hα line spectroscopic observations of a filament one day before its eruption. The observations were made with the IBIS interferometer at the Dunn Solar Telescope on May 29, 2017. In some positions at the filament downflows of cool plasma (of temperature of 9000 K) and rather large velocities (their LOS component exceeds 7 km/s) were found with the modelling. In other hand, plasma in other parts of the filament is almost not moving but it was heated to much higher temperatures (up to 13000 K). Such results agree with the fact that the filament is in the state of activation. Comparison of distributions of the intensities at the Hα line centre across the filament with the model suggests necessity of using a multi-slab model. Development of such model is planed in a close future. Introducing variations of temperature and pressure within individual flux-tubes is also intended.