Description: An investigation into the formation of fibrils in the solar chomosphere using the Bifrost code. The fibrils in our simulation were found to be produced by a process different to the typical formation methods previously suggested.
Journal info: Astronomy & Astrophysics, Volume 665, id.A6, 20 pp.
Authors: Druett, M. K. ; Leenaarts, J. ; Carlsson, M. ; Szydlarski, M.
Description: This paper introduces the COCOPLOT software. This method collapses one dimension of 3D data into a representative colour, and plots this over a 2D image. The image can be used to instantly understand the general shape of the data in that dimension, working similarly to the human eye. This method is used primarily to understand the spectral line shapes present in a 3D datacube with spectral information on the collapsed axis and the image in the remaining two dimensions, see image below.
Journal info: RAS Techniques and Instruments, Vol. 1, Issue 1, pp. 29-42
Authors: Druett, Malcolm K. ; Pietrow, Alexander G. M. ; Vissers, Gregal J. M. ; Robustini, Carolina ; Calvo, Flavio
Description: Using highly broadened spectral line emission as "pseudo-continuum" backlighting we were able to provide the first observational estimate of the mass in a fan jet, which is a plasma jet situated over a sunspot lightbrige. State-of-the-art inversions of other spectral lines corroborated the validity of our assumptions. This novel approach to a unique observation was praised by the anonymous reviewer as, “a result of substantial importance for solar physics”. I designed this project independently, it was conducted and developed together by Alex Pietrow, a PhD student at the time, with me as supervisor.
Journal info: Astronomy & Astrophysics, Volume 659, id.A58, 12 pp.
Authors: Pietrow, A. G. M. ; Druett, M. K. ; de la Cruz Rodriguez, J. ; Calvo, F. ; Kiselman, D.
Description: Interpretation of the observations of the flare from 6 September 2017 reported in Paper I. These include gamma-ray (GR), hard X-ray (HXR), soft X-rays, Lyα line, extreme ultraviolet (EUV), Hα, and white light (WL) emission
Journal info: Astronomy & Astrophysics, Volume 639, id.A79, 20 pp.
Authors: Zharkova, Valentina ; Zharkov, Sergei ; Druett, Malcolm ; Matthews, Sarah ; Inoue, Satoshi
Description: We employed non-linear force-free field extrapolations followed by magnetohydrodynamic simulations in order to identify the presence of several magnetic flux ropes prior to the initiation of this X9.3 flare. Sunquakes were observed using the directional holography and time-distance diagram detection techniques. For each flaring event we detect a few seismic sources, or sunquakes, using Dopplergrams from the HMI/SDO instrument coinciding with the kernels of Hα line emission with strong redshifts and white light sources.
Journal info: Astronomy & Astrophysics, Volume 639, id.A78, 19 pp.
Authors: Zharkov, Sergei ; Matthews, Sarah ; Zharkova, Valentina ; Druett, Malcolm ; Inoue, Satoshi ; Dammasch, Ingolf E. ; Macrae, Connor
Description: During an electron beam injection (impulsive) phase of a flare the Lyman continuum emission is greatly enhanced in a large range of wavelengths resulting in a flattened distribution of Lyman continuum over wavelengths. After the beam is switched off, Lyman continuum emission, because of its large opacity, sustains, for a very long time, the high ionisation degree of the flaring plasma gained during the beam injection. This leads to a long enhancement of hydrogen ionisation, the occurrence of white light flares, and an increase of Lyman line emission in cores and wings. Lyman line shapes are moved closer to those from complete redistribution (CRD) in frequencies, and away from the partial ones (PRD) derived in the non-flaring atmospheres. In addition, Lyman line profiles can reflect macro-motions of a flaring atmosphere caused by downward hydrodynamic shocks produced in response to the beam injection reflected in the enhancements of Ly-line red wing emission.
Journal info: Astronomy & Astrophysics, Volume 623, id.A20, 22 pp.
Description: Introduction to the HYDRO2GEN code: Flaring atmospheres are considered to be produced by a 1D hydrodynamic response to the injection of an electron beam defining their kinetic temperatures, densities, and macro velocities. We simulated a radiative response in these atmospheres using a fully non-local thermodynamic equilibrium (NLTE) approach for a 5-level plus continuum hydrogen atom model, considering its excitation and ionisation by spontaneous, external, and internal diffusive radiation and by inelastic collisions with thermal and beam electrons. Simultaneous steady-state and integral radiative transfer equations in all optically thick transitions (Lyman and Balmer series) were solved iteratively for all the transitions to define their source functions with the relative accuracy of 10-5. The solutions of the radiative transfer equations were found using the L2 approximation. Resulting intensities of hydrogen line and continuum emission were also calculated for Balmer and Paschen series.
Journal info: Astronomy & Astrophysics, Volume 610, id.A68, 29 pp.
Description: The X2.1 class flare that occurred on September 6, 2011 was associated with the first of two homologous white light flares produced by this region, but no sunquake was found with it despite the one being detected in the second flare of 7 September 2011. In this paper we present the first observation of a sunquake for the 6 September 2011 flare detected via statistical significance analysis of egression power and verified via directional holography and time-distance diagram.
Journal info: Astronomy & Astrophysics, Volume 619, id.A65, 14 pp.
Authors: Macrae, Connor ; Zharkov, Sergei ; Zharkova, Valentina ; Druett, Malcolm ; Matthews, Sarah ; Kawate, Tomoko
Description: The observations of solar flare onsets show rapid increase of hard and soft X-rays, ultra-violet emission with large Doppler blue shifts associated with plasma upflows, and Hα hydrogen emission with red shifts up to 1-4 Å. Modern radiative hydrodynamic models account well for blue-shifted emission, but struggle to reproduce closely the red-shifted Hα lines. Here we present a joint hydrodynamic and radiative model showing that during the first seconds of beam injection the effects caused by beam electrons can reproduce Hα line profiles with large red-shifts closely matching those observed in a C1.5 flare by the Swedish Solar Telescope. The model also accounts closely for timing and magnitude of upward motion to the corona observed 29 s after the event onset in 171 Å by the Atmospheric Imaging Assembly/Solar Dynamics Observatory.
