Source-linked AI summary
Discovery of multi-temperature coronal mass ejection signatures from a young solar analogue
Kosuke Namekata, Kevin France, Jongchul Chae, Vladimir S. Airapetian, Adam Kowalski, Yuta Notsu, Peter R. Young, Satoshi Honda, Soosang Kang, Juhyung Kang, Kyeore Lee, Hiroyuki Maehara, Kyoung-Sun Lee, Cole Tamburri, Tomohito Ohshima, Masaki Takayama, Kazunari Shibata
TL;DR
The paper examines how fast, warm and slow, cool blueshifted components observed in EK Draconis are connected. Multi-wavelength spectroscopy identifies related eruptive signatures, supporting a multi-temperature, multi-component stellar CME interpretation.
Problem
The connection between the cool and warm plasma components in the observed eruption is difficult to reconcile with a single plasma-evolution scenario.
Method
The study combines HST FUV spectroscopy with optical Hα observations and analyzes blueshifted line profiles to characterize the eruptive plasma components.
Results
Warm plasma shifts from –300 to –550 km s−1, while cooler plasma shifts at –60 to –70 km s−1 about 10 minutes later; their estimated masses are comparable, but the warm component carries more kinetic energy.
Takeaways & Limitations
The observations provide evidence for multi-temperature structures in stellar CME-related phenomena involving fast, warm plasma and slow, cool plasma.
Takeaways & Limitations
The prolonged Hα blueshift has an unclear mechanism, with possible explanations including continuous external forcing or preferential fading of faster components.
Abstract
from arXiv · showhide
Coronal mass ejections (CMEs) on the early Sun may have profoundly influenced the planetary atmospheres of early Solar System planets. Flaring young solar analogues serve as excellent proxies for probing the plasma environment of the young Sun, yet their CMEs remain poorly understood. Here we report the detection of multi-wavelength Doppler shifts in Far-Ultraviolet (FUV) and optical lines during a flare on the young solar analog EK Draconis. During and before a Carrington-class ($\sim$10$^{32}$ erg) flare, warm FUV lines ($\sim$10$^5$ K) exhibit blueshifted emission at 300-550 km s$^{-1}$, indicative of a warm eruption. 10 minutes later, the H$α$ line shows slow (70 km s$^{-1}$), long-lasting ($\gtrsim$2 hrs) blueshifted absorptions, suggesting a cool ($\sim$10$^4$ K) filament eruption. This provides evidence of multi-temperature and multi-component nature of a stellar CME. If Carrington-class flares/CMEs occurred frequently on the young Sun, they may have cumulatively impacted the early Earth's magnetosphere and atmosphere.
Results
EK Dra showed coordinated Doppler signatures across FUV emission and optical Hα absorption during a major flare, revealing fast warm and slower cool eruptive plasma.
- Results: −300 to −550 km s−1 blueshifted FUV components appeared in C III and Si IV during the flare, with maxima reaching −690 km s−1.C III also showed comparable blueshifts during the pre-flare brightening phase.
- Results: About 10 minutes after the FUV flare, Hα developed −60 to −70 km s−1 blueshifted absorption that persisted for roughly two hours.The absorption was independently confirmed with two high-resolution spectrographs.
- Results: The combined FUV and Hα blueshifts constitute a multi-wavelength detection of CME-related phenomena in a young solar analogue.The FUV signatures trace warm plasma, while the delayed Hα absorption traces a distinct cooler component.
Discussion
The observations support related but distinct fast warm and slow cool components in an EK Dra eruption, while leaving their precise physical connection unresolved. Their apparent frequency suggests that Carrington-class eruptions could cumulatively affect young planetary environments.
- Discussion: The FUV interpretation is most consistent with flare-associated CMEs rather than chromospheric evaporation, because the observed warm-line blueshifts are extended and too strong for the alternative mechanisms considered.The comparison X9.0-class solar flare lacked extended blueshifted wings in comparable warm lines.
- Discussion: The Hα signal is best explained by a filament eruption, but its unusually long, nearly constant-velocity absorption remains dynamically uncertain.Possible explanations include continuous external forcing or preferential fading of faster components; the duration is more consistent with CME events than confined eruptions.
- Discussion: The FUV and Hα signatures likely arise from distinct plasma components because the velocity changes from −300 to −550 km s−1 to −60 to −70 km s−1 within 10 minutes.A single decelerating component would require >0.60 km s−2, exceeding EK Dra’s surface gravity of 0.30±0.05 km s−2.
- Discussion: The warm and cool components may be different atmospheric layers of one event or distinct yet connected eruptions, including a possible sympathetic eruption.Independent eruptions remain statistically unlikely, with a 3.4% probability of occurring within 10 minutes at the stated event rate.
- Discussion: The warm plasma carries more kinetic energy, (1.1–4.9) × 10^31 erg, than the cool plasma, (0.19–9.0) × 10^30 erg, despite comparable estimated masses.The estimated warm-plasma mass is (4.0–7.6) × 10^16 g and the cool-plasma mass is (0.93–31) × 10^16 g.
- Discussion: The cool component’s kinetic energy is about two orders of magnitude below solar scaling predictions, whereas the warm component agrees more closely with the expected relation.This supports interpreting the cool plasma as the slower lower part of the CME rather than a separately suppressed eruption.
- Discussion: CME-related eruptions appear relatively common above ∼10^31 erg, including Carrington-class flares that are 2–3 orders of magnitude weaker than the largest young-solar-analogue flares.The authors suggest weaker magnetic suppression in EK Dra’s mixed open and closed field configuration may permit frequent eruptions.
- Discussion: If Carrington-class CMEs were common on the young Sun, their cumulative shocks, magnetospheric compression, and energetic-particle precipitation could affect early atmospheric chemistry.The paper estimates possible magnetic storms of ∼0.5–1 per day and magnetospheric compression to ∼2 R_E.
Methods
The study combines time-resolved FUV and optical spectroscopy with solar comparisons and plasma modeling to characterize flare-associated eruptions on EK Dra. It estimates flare energetics, warm-plasma properties, and cool-filament mass and kinetic energy while documenting observational and modeling assumptions.
- FUV Spectroscopic Data Analysis: FUV spectra were obtained with HST/COS G130M at 30-second cadence, calibrated for instrumental response, stellar motion, timing, and quiescent reference spectra.C III and Si IV profiles were fit with Gaussian models after accounting for the COS line-spread function.
- FUV Spectroscopic Data Analysis: Additional FUV wing diagnostics found tentative blueshifted enhancements in Lyα, C II, and Si IV 1402.8 Å, while blending, weak lines, and noise limited interpretation.The strongest analyzed FUV lines remained C III and Si IV.
- Hα Spectroscopic Data Analysis: Coordinated BOES, MALLS, and KOOLS-IFU observations supplied Hα spectra with complementary resolution and cadence, with BOES providing the primary analysis and MALLS supportive confirmation.Telluric contamination limited detailed fitting of the MALLS spectra, while KOOLS-IFU was mainly used for light curves.
- Emission Mechanism of the Long-Duration Hα Flare: The long-duration Hα-bright flare was discussed using three possibilities: behind-the-limb geometry, an exceptional Neupert-effect relation, or a low-heating-rate non-white-light flare.The passage presents these as alternative interpretations rather than selecting one mechanism.
- Flare Energy Calculation: The continuum-based flare-energy estimate is systematically uncertain because stellar flare spectra can include optically thin, multi-kernel, or non-blackbody components.The authors estimate blackbody-assumption uncertainties at roughly a factor of a few rather than orders of magnitude.
- Flare Energy Calculation: 2.3 ± 1.1 × 10^32 erg was estimated from a 12,900 ± 500 K blackbody fit to the FUV continuum, corresponding to approximately X23 in the GOES classification.The inferred flare area was 1.8 ± 0.6 × 10^18 cm^2, and a solar-flare comparison supported the energy estimate.
- Plasma Mass Estimation: The warm eruptive component was modeled from C III and Si IV luminosities using CHIANTI emissivities, yielding log n_e = 9.3, M_Si IV = (4.0–7.6) × 10^16 g, and E_kin,Si IV = (1.1–4.9) × 10^31 erg.These values assume optically thin emission and V_Si IV = −300 ± 60 km s−1; higher-density alternatives produced lower masses and kinetic energies.
- Plasma Mass Estimation: The cool filament properties were estimated from Hα absorption using Becker’s cloud model, giving mass (0.93–31) × 10^16 g, length scale (0.36–14) × 10^10 cm, and kinetic energy (0.19–9.0) × 10^30 erg.The conservative estimate used an absorption EW of 0.013 ± 0.005 Å and velocity 70 ± 7 km s−1, with uncertainties spanning assumed model parameters.
Data Availability
The paper provides source data and archive access for its figures and observations.
- Data Availability: Source data accompany the paper, while raw ground-based spectra and TESS, HST, and IRIS data are available through observatory or mission archives or by author request.The listed resources include SMOKA, MAST, the Virtual Solar Observatory, and the Lockheed Martin Solar Astrophysics Laboratory archive.
Figures
The figures track blueshifted FUV emission, delayed Hα absorption, and their velocity evolution, while extending the analysis to spectral quality, flare energetics, and solar comparisons.
- FUV spectroscopy: FUV spectra isolate blueshifted C III and Si IV components across pre-flare brightening and flare phases using Gaussian decomposition.Extended data establish that the blue-wing emission remains significant above flux errors despite broader profiles and blending.
- Optical spectroscopy: About ten minutes after the FUV flare, Hα develops a blueshifted absorption component that persists for roughly two hours.The Hα dynamic spectrum compares absorption and emission relative to the quiescent spectrum and overlays the FUV component velocities.
- Velocity evolution: FUV blueshift velocities precede the Hα signal, and schematic panels present either layered plasma in one eruption or distinct but connected eruptions.The warm component becomes faint in FUV line wings after about ten minutes, plausibly because of expansion.
- Additional FUV lines: Additional FUV diagnostics show possible blue-wing features in Lyα and C II, while blending, contamination, and data quality limit interpretation of several lines.N V lacks a significant blueshifted enhancement, and Si IV 1402 Å is excluded from velocity analysis because of O IV blending.
- Energetics and comparison: The figures estimate the flare’s bolometric white-light energy and compare Hα- and FUV-derived eruption properties with solar filament, prominence, and CME relations.The comparison adopts stated bolometric-to-GOES scaling relations and assumes bolometric energy approximately equals bolometric white-light flare energy.