Identification and characteristics of H-alpha and H-beta wing fibrils

Spectrally resolved images in the wings of strong chromospheric lines show many narrow, highly collimated dark structures, seen most prominently around plage and network regions. While there is a stable distribution of these features around any given magnetic field concentration, individual “wing fibrils” often have short lifetimes and show rapid evolution (e.g. RBEs, RREs, curtains etc). Interestingly, these fibrils can be clearly identified in maps of spectral-line widths of the same chromospheric lines, or in images through broader interference filters, possibly indicating sites of enhanced heating.

To understand better the nature of these fibrils, we have explored techniques for their identification and characterization. In particular, we have made use of automatic segmentation tools suited for extracting curvilinear structures, such as OCCULT2 (Aschwanden et al. 2013). Using the extracted fibril locations, we can then determine parameters such as their length and breadth, as well as compare their location with other diagnostics. We perform this analysis on a time series of H-alpha spectral line-width maps taken at 70 km spatial resolution and four second cadence, in order to understand their evolution in time. Finally, we apply this technique to images of these fibrils taken with the H-beta filter of the Visible Broadband Imager (VBI) on DKIST to probe their characteristics at even higher spatial resolutions.