Bibcode
Libbrecht, T.; Joshi, J.; de la Cruz Rodríguez, J.; Leenaarts, J.; Asensio-Ramos, A.
Bibliographical reference
Astronomy and Astrophysics, Volume 598, id.A33, 15 pp.
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1
2017
Journal
Citations
31
Refereed citations
30
Description
Context. Ellerman bombs (EBs) are short-lived emission features,
characterised by extended wing emission in hydrogen Balmer lines. Until
now, no distinct signature of EBs has been found in the He i 10 830
Å line, and conclusive observations of EBs in He i D3
have never been reported. Aims: We aim to study the signature of
EBs in neutral helium triplet lines. Methods: The observations
consisted of ten consecutive SST/TRIPPEL raster scans close to the limb,
featuring the Hβ, He i D3 and He i 10 830 Å
spectral regions. We also obtained raster scans with IRIS and made use
of the SDO/AIA 1700 Å channel. We used 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 blueshifted 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 2 × 104-105
K.
Movies associated to Figs. 3-5 are available at http://www.aanda.org
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