Chromospheric multi-wavelength observations near the solar limb

TL;DR

This study demonstrates simultaneous adaptive optics-corrected multi-wavelength spectroscopic observations of the solar chromosphere near the limb, revealing dynamic structures like macrospicules and wave motions.

Contribution

It introduces a method for obtaining synchronized AO-corrected spectra in multiple chromospheric lines at the solar limb, enabling detailed analysis of chromospheric dynamics.

Findings

Detection of macrospicule signatures in four chromospheric lines.

Observation of small-scale Doppler shift variations indicating coherent rotating structures.

Evidence of upward propagating helical waves on flux tube surfaces.

Abstract

Observations of chromospheric spectral lines near and beyond the solar limb provide information on the solar chromosphere without any photospheric contamination. For ground-based observations near and off the limb with real-time image correction by adaptive optics (AO), some technical requirements have to be met, such as an AO lock point that is independent of the location of the field of view observed by the science instruments, both for 1D and 2D instruments. We show how to obtain simultaneous AO-corrected spectra in Ca II H, Ha, Ca II IR at 854 nm, and He I at 1083 nm with the instrumentation at the German Vacuum Tower Telescope in Izana, Tenerife. We determined the spectral properties of an active-region macrospicule inside the field of view in the four chromospheric lines, including its signature in polarization in He I at 1083 nm. Compared to the line-core intensities, the Doppler shifts of the lines change on a smaller spatial scale in the direction parallel to the limb, suggesting the presence of coherent rotating structures or the passage of upwards propagating helical waves on the surfaces of expanding flux tubes.