Magnetic Field Configuration of a Quiescent Prominence Revealed by Large-amplitude Longitudinal Oscillations in End-view Observations

TL;DR

The paper tackles how to infer the 3D magnetic-field geometry of a quiescent solar prominence by exploiting large-amplitude longitudinal oscillations observed from end-view. It combines CHASE/HIS spectroscopic data with SDO/AIA imaging to derive both Doppler and plane-of-sky velocities, then uses three complementary methods—pendulum-model seismology, time-distance-based curvature estimates, and velocity-field/Doppler analyses—to determine the curvature radius and geometry of the supporting magnetic dips. The authors find that the dips are sinusoidal, with a curvature radius that evolves from ~$90$ Mm at the bottom to ~$220$ Mm in the middle and down to ~$10$–$40$ Mm near the top, and a transverse field of about $22$–$25$ G. They also identify a triggering mechanism in which collision and heating of an adjoining hot structure associated with two coronal jets initiates the LAOs, highlighting end-view observations as a powerful tool for prominence seismology and magnetic-field diagnostics.

Abstract

Prominence seismology, applied to the large-amplitude longitudinal oscillation, is used to indirectly diagnose the geometry and strength of the magnetic fields inside the prominence. In this paper, combining imaging and spectroscopic data, the magnetic field configuration of a quiescent prominence is revealed by large-amplitude longitudinal oscillations observed in end view on 2023 December 4. Particularly, the prominence oscillation involved blueshift velocities in Dopplergrams and horizontal motions in extreme-ultraviolet (EUV) images. Originally, the prominence oscillation was triggered by the collision and heating of an adjoining hot structure associated with two coronal jets. The oscillation involved two groups of signals with similar oscillatory parameters, a three-dimensional (3D) initial amplitude of 40 Mm and a 3D velocity amplitude of 48 km/s, both lasting for 4 cycles with a period of 77 minutes, with a phase difference of pi/4. While the angle between 3D velocities and the prominence axis ranges from 10 to 30. Two methods, utilizing time-distance diagrams and velocity fields, are employed to calculate the curvature radius of magnetic dips supporting the prominence materials. Both methods yield similar value ranges and trends from the bottom to the top of magnetic dips, with the curvature radius increasing from 90 Mm to 220 Mm, then decreasing to 10 Mm, with transverse magnetic field strength 25 Gauss. From this, the realistic 3D geometry of the prominence magnetic dips is determined to be sinusoidal. To the best of our knowledge, we present the first accurate calculation of the 3D curvature radius and geometry of the prominence magnetic dips based on longitudinal oscillatory motions.

Figures (7)

• Figure 1: The triggering process of the prominence oscillation. Panels (a1-a3) give three EUV images in AIA 304 Å. The yellow arrows point to the coronal jets and the displacement of the prominence materials, respectively. Panels (b1-b3) give three EUV images in AIA 94 Å. The white arrows point to the hot structure. The yellow ellipses in panel (a1-a2) and (b2) mark the brightening region inside the prominence. The yellow dashed lines in panels (a3-b2) represent the rising track of the two coronal jets. Panels (c-d): Time-distance diagrams of the slices S1 and S2 in AIA 304 Å. The yellow arrows in panels (c-d) mark the start times and different phases of the coronal jets; Panels (e1-e2): Time-distance diagrams of the slice AB in AIA 94 Å and 131Å. The two yellow parallelograms in panel (e1) mark the propagation of the hot structure. The blue parallelogram in panel (e2) outlines the interaction brightening between the hot structure and the prominence. (An animation of this figure is available.)
• Figure 2: Panel (a): An EUV image in AIA 171 Å of the oscillating prominence. Panel (b): A Dopplergram showing the velocities of the oscillating prominence materials. Panel (c): Time-distance diagrams of the slice CD in AIA 171 Å. The green and magenta crosses outline the prominence oscillations OS1 and OS2 between 11:30 UT and 17:30 UT, respectively. Panel (d): Time-distance diagrams of the slice CD in Dopplergrams, where the three periods are 12:25 - 12:45 UT, 14:00 - 14:25 UT, 15:35 - 15:55 UT, respectively. The extracted positions of OS1 and OS2 in panel (c) are overlaid with green and magenta crosses, and the fitted curves are overlaid with green and magenta dotted lines, respectively. Corresponding parameters are labeled. (An animation of this figure is available.)
• Figure 3: The axial direction of the prominence and the velocities of the oscillation. Panel (a) gives an H$\alpha$ line-center image in 6562.82 Å observed by CHASE on 2023 December 01 at $\sim$12:00 UT. The blue contour outlines the profile of the prominence when it was on the solar disk. The blue solid dots in panel (b) represent the extracted location of the prominence spine from panel (a), and have been rotated to the center of the solar disk (corresponding to the top view) in the coordinate system. The red dashed and solid lines mark the axial direction of the prominence spine and the LOS direction when they are projected on the disk, respectively. Panel (c) gives a schematic diagram showing the angles between the prominence axis and oscillatory velocities. The gray rectangle represents the plane of sky. POS west, north, and LOS directions are taken as x-, y-, and z-axes. The blue, red, and orange solid arrows indicate the POS velocity, Doppler velocity, and 3D velocity of oscillatory materials, respectively. The Doppler velocity and the prominence axis are coplanar in the red rectangle (Plane A), which is perpendicular to the plane of sky. The angle between POS velocity and y-axes, Plane A are marked as $\beta$ and $\gamma$, respectively. $\alpha$ represents the angle between the prominence axis and the direction of the 3D velocity.
• Figure 4: Panels (a1-b1): Velocity-time plot of $V_{POS}$, $V_{LOS}$, $V_{3D}$. The values in panel (a1) were obtained from slice CD, while the values in panel (b1) were obtained from the simultaneous POS velocity fields and Dopplergrams of the oscillatory prominence materials. Panels (a2-b2): Evolution of the angle $\alpha$ and local curvature radius of magnetic dip, where the values were estimated from the velocities in panels (a1) and (b1), respectively.
• Figure 5: The elevation angle $\theta$ and azimuth angle $\psi$ ($\beta$ in Figure \ref{['fig3']} ) of $V_{3D}$ in right-hand coordinate system.