High-resolution Imaging Spectroscopy of a Tiny Sigmoidal Minifilament Eruption

Minifilament eruptions producing small jets and microflares have mostly been studied based on coronal observations at extreme-ultraviolet and X-ray wavelengths. This study presents chromospheric plasma diagnostics of a quiet-Sun minifilament of size ∼ 2″ × 5″ with a sigmoidal shape and an associated microflare observed on 2021 August 7 17:00 UT using high temporal and spatial resolution spectroscopy from the Fast Imaging Solar Spectrograph (FISS) and high-resolution magnetograms from the Near InfraRed Imaging Spectropolarimeter (NIRIS) installed on the 1.6 m Goode Solar Telescope at Big Bear Solar Observatory. Using FISS Hα and Ca ii 8542 Å line spectra at the time of the minifilament activation we determined a temperature of 8600 K and a nonthermal speed of 7.9 km s⁻¹. During the eruption, the minifilament was no longer visible in the Ca ii 8542 Å line, and only the Hα line spectra were used to find the temperature of the minifilament, which reached 1.2 × 10⁴ K and decreased afterward. We estimated thermal energy of 3.6 × 10²⁴ erg from the maximum temperature and kinetic energy of 2.6 × 10²⁴ erg from the rising speed (18 km s⁻¹) of the minifilament. From the NIRIS magnetograms we found small-scale flux emergence and cancellation coincident with the minifilament eruption, and the magnetic energy change across the conjugate footpoints reaches 7.2 × 10²⁵ erg. Such spectroscopic diagnostics of the chromospheric minifilament complement earlier studies of minifilament eruptions made using coronal images.