HOP 0382

abstract of observational proposal

Scientific Justification: Parker [1978ApJ...221..368P] suggested as a process of magnetic field intensification the now so-called convective collapse process, where a magnetic flux tube seated in the intergranular lane is initially exposed to a strong downdraft evacuating the tube. To restore equilibrium between the inner tube atmosphere and the outer pressure field the magnetic field, and therefore the magnetic pressure in the tube increases, leading to the observed kG flux tubes. The magnetic flux stays constant during the process with the radial size of the flux tube shrinking. Indirect observational confirmation of this magnetic field intensification process was obtained by e.g., Bellot Rubio et al. [2001ApJ...560.1010B] and direct observations were obtained by Nagata et al. [2008ApJ...677L.145N] using data from Hinode. The statistical study by Fischer et al. [2009A&A...504..583F] has shown the frequent occurrence of this process.

We will obtain GERGOR IFU data at very high spectral and spatial resolution to determine the fine structure of the magnetic elements undergoing convective collapse. The high spatial resolution will allow us to study the substructures within the magnetic element and the high spectral resolution allows to analyse Stokes profile asymmetries. For example, asymmetric circular polarisation profiles recorded during the convective collapse events reveal a complex atmospheric structure and could be indications of a rebound shock produced when the downwards moving mass “bounces” of the lower layers (as suggested by Bellot Rubio et al.[2001ApJ...560.1010B] ). We will address questions such as what causes the oscillations in the physical parameters as observed by e.g. Fischer et al. [2009A&A...504..583F] and can one detect energy transport to higher atmospheric layers? We would like to sample the magnetic elements at different heights to study their dynamics by using, in addition to the GREGOR infrared data, Hinode SP data in the visible wavelength range of 630 nm. Simultaneous measurements with the IRIS telescope will be used to analyse the chromospheric response to these events and study the velocity flows in the chromosphere and transition region.

remarks

Dates: (1) Co-Observing from 12 till 19 August, 2019. This is the timeslot allocated for the observations at the GREGOR telescope. 2. It is not necessary for observations to be on consecutive days

Time window: 1. Co-observing with GREGOR start: 7 UT end: 11:30 UT. Based on the lifetimes of the events we would need a minimum duration of 30 minutes. 2. If possible we would like to avoid interruptions.

Target(s) of interest: 1. quiet Sun at disk center

Previous HOPs: HOP 141, ToO run 2 times