Observations of Ellerman bomb emission features in He I D3 and He I 10830 {\AA}

TL;DR

This study reports the first clear detection of Ellerman bombs in neutral helium triplet lines, revealing their high-temperature nature and complex velocity structures through detailed spectroscopic analysis.

Contribution

It provides the first conclusive observations of EBs in He I D3 and 10830 Å lines, demonstrating their emission signatures and thermal properties in these spectral features.

Findings

EBs show distinct emission in He I D3 and 10830 Å lines.

Helium lines exhibit broad, blue-shifted emission and narrow absorption components.

EB temperatures estimated between 20,000 and 100,000 K.

Abstract

Context. Ellerman bombs (EBs) are short-lived emission features, characterized by extended wing emission in hydrogen Balmer lines. Until now, no distinct signature of EBs has been found in the He I 10830 {\AA} line, and conclusive observations of EBs in He I D 3 have never been reported. Aims. We aim to study the signature of EBs in neutral helium triplet lines. Methods. The observations consist of 10 consecutive SST/TRIPPEL raster scans close to the limb, featuring the H$\beta$, He I D3 and He I 10830 {\AA} spectral regions. We also obtained raster scans with IRIS and make use of the SDO/AIA 1700 {\AA} channel. We use Hazel to invert the neutral helium triplet lines. Results. Three EBs in our data show distinct emission signatures in neutral helium triplet lines, most prominently visible in the He I D3 line. The helium lines have two components: a broad and blue-shifted emission component associated with the EB, and a narrower absorption component formed in the overlying chromosphere. One of the EBs in our data shows evidence of strong velocity gradients in its emission component. The emission component of the other two EBs could be fitted using a constant slab. Our analysis hints towards thermal Doppler motions having a large contribution to the broadening for helium and IRIS lines. We conclude that the EBs must have high temperatures to exhibit emission signals in neutral helium triplet lines. An order of magnitude estimate places our observed EBs in the range of $T\sim 2\cdot 10^4-10^5$ K.