Ellerman bombs at high resolution. IV. Visibility in Na I and Mg I

TL;DR

This study confirms Ellerman's observation that Ellerman bombs are not visible in Na I D and Mg I b lines using high-resolution imaging, and explores the nature of diffuse brightness in these lines related to prior EBs.

Contribution

The paper provides high-resolution observational evidence supporting Ellerman's original claim about the non-visibility of EBs in certain spectral lines and investigates the origin of diffuse brightness in these lines.

Findings

Ellerman bombs are not visible in Na I D and Mg I b lines.

Diffuse brightness in these lines may result from prior EBs.

Post-bomb hot-cloud phenomena are observed in ultraviolet spectroscopy.

Abstract

Ellerman bombs are transient brightenings of the wings of the solar Balmer lines that mark reconnection in the photosphere. Ellerman noted in 1917 that he did not observe such brightenings in the Na I D and Mg I b lines. This non-visibility should constrain EB interpretation, but has not been addressed in published bomb modeling. We therefore test Ellerman's observation and confirm it using high-quality imaging spectrometry with the Swedish 1-m Solar Telescope. However, we find diffuse brightness in these lines that seems to result from prior EBs. We tentatively suggest this is a post-bomb hot-cloud phenomenon also found in recent EB spectroscopy in the ultraviolet.