Doppler velocity oscillations in an Hα network rosette

Abstract

Magnetic flux tubes such as sunspots play the role of channels through which magnetohydrodynamic waves carry mechanical energy from the solar interior to the atmosphere. We investigate the spatial distribution of Doppler velocity oscillations in the chromospheric network rosette, a supposed quiet Sun miniature of a sunspot, by analyzing Hα line spectral data taken with the Fast Imaging Solar Spectrograph of the Goode Solar Telescope. The rosette consists of two regions: a central region displaying Hα emission and a fibril region displaying Hα absorption. We have categorized the observed velocity oscillations into three groups depending on location and period. Group I oscillations with periods from 3 to 6 min occur in the central region, group II oscillations with periods from 6 to 20 min in the inner parts of the fibril region, and group III oscillations with periods shorter than 3 min in the outermost parts of the fibril region. We discuss the probable physical origin of oscillations of each group. Our results suggest that the rosette is similar to a sunspot in morphology and oscillation properties, but there exist differences as well.