Analysis of UV and EUV emission from impacts on the Sun after 2011 June 7 eruptive flare

Abstract

On 2011 June 7 debris from a large filament eruption fell back to the Sun causing bright ultraviolet (UV) and extreme ultraviolet (EUV) splashes across the surface. These impacts may give clues on the process of stellar accretion. The aim is to investigate how the impact emission is influenced by structures in the falling ejecta and at the solar surface. We determine the UV and EUV light curves of a sample of impacts. The ballistic impact velocity is estimated from the ejection and landing times and, where possible, compared with the velocity derived by tracking the downflows in SDO/AIA and STEREO/EUVI images. Estimates of the column density before impact are made from the darkness of the falling plasma in the 193 A channel. The impact velocities were between 230 and 450 km/s. All impacts produced bright EUV emission at the impact site but bright UV was only observed when the impacting fragments reached the chromosphere. There was no clear relation between EUV intensity and kinetic energy. Low UV to EUV intensity ratios (I{UV}/I{EUV}) were seen (i) from impacts of low column-density fragments, (ii) when splashes, produced by some impacts, prevented subsequent fragments from reaching the chromosphere, and (iii) from an impact in an active region. The earliest impacts with the lowest velocity (~250 km/s) had the highest I{UV}/I{EUV}. The I{UV}/I{EUV} decreases with impact velocity, magnetic field at the impact site, and EUV ionising flux. Many of the infalling fragments dissipate above the chromosphere either due to ionisation and trapping in magnetic structures, or to them encountering a splash from an earlier impact. If the same happens in accreting stars then the reduced X-ray compared to optical emission that has been observed is more likely due to absorption by the trailing stream than locally at the impact site.

10 pages, 14 figures To be published in A&A

References in corpus (5)

• X-ray emission from dense plasma in CTTSs: Hydrodynamic modeling of the accretion shock
• Coronal magnetic reconnection driven by CME expansion -- the 2011 June 7 event
• Mass estimates of rapidly-moving prominence material from high-cadence EUV images
• Bright hot impacts by erupted fragments falling back on the Sun: UV redshifts in stellar accretion
• Magnetohydrodynamic modeling of the accretion shocks in classical T Tauri stars: the role of local absorption on the X-ray emission

Cited by in corpus (9)

• Observation of all pre- and post-reconnection structures involved in three-dimensional reconnection geometries in solar eruptions
• Enhancement of a sunspot light wall with external disturbances
• Plasma Brightenings in a Failed Solar Filament Eruption
• Radio, EUV, and X-Ray Observations During a Filament Rise in the 2011 June 7 Solar Flare
• Dropouts of Fully Stripped Ions in the Solar Wind: A Diagnostic for Wave Heating versus Reconnection
• Three-dimensional, Time-dependent MHD Simulation of Disk-Magnetosphere-Stellar Wind Interaction in a T Tauri, Protoplanetary System
• Remote Sensing of Coronal Forces During a Solar Prominence Eruption
• Observations of the formation of a proto-spot in a pre-existing field environment
• Energy release in the solar atmosphere from a stream of infalling prominence debris