Top panel: Zoomed-in view of Hα filtergram for reference. Middle panel: GRIS slit-reconstructed He I line core intensity of the RoI acquired between 09:17:32 and 09:37:05 UT on November 10. Bottom panel: Stokes-I profiles, normalized to continuum intensity, observed at the red, blue, and orange (1, 2, and 3) positions shown in the He I line core map. Arrows point to thin, darker, elongated threads where the optical thickness of the He I line is higher than their own surroundings (Fig. 4). White contours represent a plasma velocity of about −1 km s⁻¹. The shaded area indicates where the He I line core is calculated (see Sect. 3.2 for more details). The vertical lines represent the rest wavelengths for the three He I components as reported in Table 1 of Kuckein et al. (2012).

Fig. 4.

He I Doppler velocity and optical thickness of GRIS observation, as calculated using the HAZEL code. Black and red contours represent plasma velocity of −1 km s⁻¹. Green and yellow contours indicate plasma velocities greater than 10 and 15 km s⁻¹.