Tracing a Multi-Temperature Quiescent Prominence's Thermodynamic Evolution from Sun to Earth

TL;DR

This study investigates a rare quiescent prominence eruption that preserves low-ionization material into interplanetary space. By combining multi-viewpoint EUV remote observations with in situ charge-state measurements at L1 and non-equilibrium ionization modeling, the authors derive radial thermodynamic profiles and reproduce the observed C, O, and Fe charge-state distributions with a two-temperature plasma (cool component at $T_e \,\approx\,1.8$ MK and hot component at $T_e \,\approx\,4.3$ MK) in a $70:30$ ratio. The results imply non-uniform heating or differential cooling within the prominence and provide freeze-in distances spanning $1.5$ to $>15\,R_igodot$, highlighting ongoing heating several solar radii from the Sun. The work underscores the need for comprehensive spectral diagnostics of the global corona to fully constrain the energy budget and thermodynamic evolution of erupting prominences.

Abstract

Solar prominences are cool, dense stable structures routinely observed in the corona. Prominences are often ejected from the Sun via coronal mass ejections (CMEs). However, they are rarely detected in a cool, low-ionized state within CMEs measured in situ, making their evolution hard to study. We examine the thermodynamic evolution of one of these rare cases where a quiescent prominence eruption clearly preserves its low-ionized charge state as evidenced by in situ detection. We use multi-viewpoint Extreme Ultraviolet (EUV) observations to track and estimate the density, temperature and speed of the prominence as it erupts. We observe that part of the prominence remains in absorption well beyond initial liftoff, indicating the bulk of the prominence experiences minimal ionization and suggesting any strong heating is balanced by radiative losses, expansion, or conduction. From its subsequent in situ passage near 1au, charge states reveal that the prominence is composed of both cool, low-ionized ions as well as hotter plasma reflected by the presence of highly ionized iron, Fe$^{16+}$. Simulated non-equilibrium ionization and recombination results using observationally derived initial conditions match the in situ multi-thermal state for a prominence composed of 70% cool plasma with a 1.8MK peak temperature, and 30% hot plasma with a 4.3MK peak temperature. This suggests that the prominence may not be heated uniformly or that parts of it cools more rapidly. The complex, multi-thermal nature of this erupting prominence emphasizes the need for more comprehensive spectral observations of the global corona.

Figures (14)

• Figure 1: Heliocentric-Earth-Ecliptic (HEE) positions of the probes used in this research on the day of the prominence eruption under investigation. We include Wind at the Earth and note that ACE was at the same location.
• Figure 2: From left to right, EUV images from the 304 Å waveband of STEREO-B, the 304 Å waveband of SDO/AIA, and the 304 Å waveband of STEREO-A. The top row shows an early time in the eruption, while the bottom row shows a timestamp exactly two hours later.
• Figure 3: From top to bottom, the figure displays the normalized charge state distributions of carbon, oxygen, and iron, proton density from ACE (black) and Wind (blue), as well as the He/H ratio (red), speed, proton temperature, magnetic field components and magnitude, and the last panel shows the column normalized electron strahl flux at 255 eV across pitch angle. The dotted red line marks the shock and start of the CME, the shaded blue regions are distinct CMEs identified in Liu2012Mostl2012, the shaded red region is the period of prominence material identified in Lepri2021.
• Figure 4: Illustration of the log of column density, L(T) or n$_{H}$, with increasing electron temperature computed using Equation \ref{['eq:simplified_f_obs_eq']} using SDO/AIA EUV emission during a snapshot of the prominence evolution. The intersection of the column density curves of different wavelength regions is used to determine the temperature and column density of the observed plasma.
• Figure 5: Two snapshots of running difference images, displaying the tracks used for AIA (A and C) and STEREO-A (B and D) at a time early on in the prominence's eruption (A and B), and again after two hours of evolution (C and D). The green 20" box in each image is a example of a box of non-prominence material we used to calculate F$_{inc}$ values.