🔭 astrophysics

Spectroscopic He I 1083 nm prominence eruption observations in the middle corona with MLSO/UCoMP

Using the Upgraded Coronal Multi-channel Polarimeter (UCoMP), this study demonstrates that He I 1083 nm observations can effectively detect neutral helium in eruptive prominences up to 2 solar radii, providing crucial spectral and velocity data to improve space weather forecasting.

Original authors: Chloe Pistelli, Momchil E Molnar, Giuliana de Toma, Joseph Plowman

Published 2026-02-11

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CC BY 4.0

Original authors: Chloe Pistelli, Momchil E Molnar, Giuliana de Toma, Joseph Plowman

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Solar "Smoke Signal": Tracking Space Weather with Helium

Imagine you are standing on a dark coastline at night, watching a massive storm roll in from the ocean. You can see the lightning (the bright flashes of solar flares), and you can see the massive waves (the Coronal Mass Ejections, or CMEs). But there is something else moving within the storm: thick, heavy clouds of mist and spray that are being thrown high into the air.

If you want to know exactly where that mist is going and how fast it’s moving, you need a special kind of flashlight—one that doesn't just show light, but shows the color of the mist itself.

This scientific paper describes how astronomers are using a new "special flashlight" called UCoMP to watch the Sun’s "mist"—specifically, cool clouds of helium—as they get blasted into space during solar eruptions.

The Problem: The Invisible Storm

When the Sun has a massive eruption (a CME), it shoots out huge bubbles of magnetic energy and plasma toward Earth. These eruptions can mess up our satellites, GPS, and power grids—this is what we call "Space Weather."

The tricky part is that these eruptions are incredibly fast and hard to track in 3D. Most of our telescopes see the "lightning" (the hot, bright parts), but they struggle to see the "mist" (the cooler, denser material) that is actually tucked inside the magnetic structure. If we don't know if that mist is heading toward Earth or flying away from us, we can't give accurate warnings.

The Solution: The Helium "Smoke Signal"

The researchers focused on a specific element: Helium.

Think of the helium in a solar eruption like smoke from a firework. Even if the firework is mostly invisible, the smoke leaves a distinct trail. By looking at a very specific "color" of light (the He I 1083 nm line), the UCoMP instrument can see this helium "smoke" even when it’s far away from the Sun.

Here is why this is a game-changer:

The Speedometer (Doppler Effect): Just like a siren changes pitch as an ambulance zooms past you (neee-oooowww!), the color of the helium light changes depending on whether it is moving toward us or away from us. By measuring this "color shift," scientists can tell if a solar eruption is a "direct hit" coming at Earth or a "miss" heading out into deep space.
The High-Definition View: While other telescopes see the corona (the Sun's atmosphere) as a blurry glow, this helium method allows scientists to see the actual "guts" of the eruption. It’s like switching from a grainy security camera to a high-definition drone shot.
The Early Warning System: Because this instrument is on the ground (in Hawaii!), it can catch these eruptions as they are just starting to leave the Sun's surface, giving us a head start on predicting space weather.

The "Rough Draft" Phase

The paper notes that the instrument is still in its "learning phase" (the commissioning phase). It’s a bit like a new professional camera that is so sensitive it occasionally "overexposes" the photo because the sun is too bright. However, even with these "blurry" photos, the scientists proved one major thing: The helium signal is incredibly strong and easy to see.

Why It Matters to You

In the future, as this technology gets refined, it will act like a high-tech radar for the Sun. Instead of just seeing a storm is coming, we will be able to see the direction, the speed, and the density of the "solar mist." This means better protection for the technology we rely on every day—from the phone in your pocket to the satellites that guide your car.

Technical Summary: Spectroscopic He I 1083 nm Prominence Eruption Observations in the Middle Corona with MLSO/UCoMP

Problem Statement

Coronal Mass Ejections (CMEs) are primary drivers of space weather, yet accurately forecasting their impact on Earth requires precise knowledge of their magnetic field structures. A significant challenge in solar physics is the "missing link" of coronal magnetic field observations. While CMEs often entrain cool, dense prominence material containing neutral elements, it has been difficult to determine how far these neutral elements (specifically helium) can be detected above the solar limb. Understanding the spatial extent and the three-dimensional velocity (line-of-sight vs. plane-of-sky) of this material is crucial for distinguishing between Earth-directed and receding CMEs.

Methodology

The study utilizes data from the commissioning phase (July 2021 – January 2022) of the Upgraded Coronal Multi-channel Polarimeter (UCoMP), a ground-based coronagraphic spectropolarimeter located at the Mauna Loa Solar Observatory (MLSO).

Spectral Line: The researchers focused on the He I 1083 nm emission line.
Data Analysis: The team analyzed 79 observing days, identifying 14 days with significant prominence eruptions. They employed a background subtraction method to estimate sky intensity as a function of height.
Multi-instrument Context: To validate and contextualize the UCoMP findings, the study integrated data from:
- MLSO/K-Cor: White-light coronagraphy to observe the CME front and plane-of-sky velocity.
- SDO/AIA: Multithermal EUV imaging (specifically 171 Å and 304 Å) to connect cool prominence plasma with hotter coronal structures.
- SOHO/LASCO: To cross-reference eruptions with established CME catalogs.
Velocity Estimation: Doppler shifts were inferred by comparing intensities across seven different wavelength positions within the He I 1083 window.

Key Contributions

Observability Demonstration: The paper establishes that neutral helium in erupting prominences is detectable in the middle corona up to approximately 2 solar radii ( $R_\odot$ ), extending significantly beyond previous instrument limits like MLSO/CHIP (1.4 $R_\odot$ ).
3D Kinematics: It demonstrates a method for combining UCoMP's line-of-sight (Doppler) velocity measurements with K-Cor's plane-of-sky velocity measurements to reconstruct the 3D motion of CMEs.
Diagnostic Robustness: The study proves that even with the technical limitations of the UCoMP commissioning phase (such as camera saturation and non-linear detection), the He I 1083 line remains a highly detectable and qualitatively useful diagnostic.

Results

High Intensity: Prominence material in the He I 1083 line was found to be extremely bright, exceeding 1,000 $\mu B_\odot$ , which is 50 to 100 times brighter than standard infrared forbidden coronal lines.
Velocity Correlation: In a specific event on July 15, 2021, the UCoMP data showed significant redshifts (velocities of several hundred km/s) in the off-band channel. This matched the K-Cor data, confirming the CME was a "fast halo" event receding from the observer (moving away from Earth).
Detection Rate: The study found that prominence eruptions were associated with CMEs in roughly 45% of the observed instances (comparing UCoMP detections to the SOHO LASCO catalog), suggesting a high correlation between neutral helium signatures and CME activity.
Structural Insights: Observations of a twisted structure on July 31, 2021, showed varying emission across different wavelength bands, providing evidence of complex, multidirectional twisting motions during the loss of magnetic equilibrium.

Significance

This research highlights the potential of ground-based spectroscopic observations to enhance space weather forecasting. By providing early and accurate identification of the direction of CMEs (distinguishing between Earth-directed and receding events) and offering a method to probe the magnetic properties of the CME core via the Hanle effect, UCoMP serves as a vital complement to space-borne observatories. The ability to detect these signatures in the middle corona provides a critical window into the early evolution of CMEs before they reach heliospheric scales.