H-alpha features with hot onsets. I. Ellerman bombs

TL;DR

Ellerman bombs are transient solar phenomena characterized by specific spectral signatures, with their formation constrained to high temperatures and densities, challenging existing models and suggesting broader implications for transient solar events.

Contribution

This paper introduces a new approach using Saha-Boltzmann populations to estimate Ellerman bomb onsets across multiple diagnostics, challenging previous assumptions.

Findings

Ellerman bombs form at temperatures of 10,000 - 20,000 K.

Hydrogen densities around 10^15 cm^-3 are involved.

Visibility varies across different spectral lines and continua.

Abstract

Ellerman bombs are transient brightenings of the wings of the Balmer lines that uniquely mark reconnection in the solar photosphere. They are also bright in strong Ca II and ultraviolet lines and in ultraviolet continua, but they are not visible in the optical continuum and the Na I D and Mg I b lines. These discordant visibilities invalidate all published Ellerman bomb modeling. I argue that the assumption of Saha-Boltzmann lower-level populations is informative to estimate bomb-onset opacities for these diverse diagnostics, even and especially for H-alpha, and employ such estimates to gauge the visibilities of Ellerman bomb onsets in all of them. They constrain Ellerman bomb formation to temperatures 10,000 - 20,000 K and hydrogen densities around 10^15 cm^-3. Similar arguments likely hold for H-alpha visibility in other transient phenomena with hot and dense onsets.