The [Fe XIII] Infrared 10747 Angstrom and 10798 Angstrom Lines in Novae

TL;DR

This study reports the first detection of [Fe XIII] infrared lines in a nova, revealing electron densities and temperatures similar to the solar corona, and suggests recurrent novae with giant secondaries as promising targets.

Contribution

The paper provides the first robust detection of [Fe XIII] lines in a nova, measuring physical conditions and linking nova coronal phases to solar corona properties.

Findings

Detected [Fe XIII] lines in V3890 Sgr at 23 and 31 days post-outburst.

Derived electron densities of 10^10 and 10^8.5-9 per cubic cm.

Estimated coronal gas temperature around 2.5 million Kelvin.

Abstract

The forbidden lines of [Fe XIII] at 10,747 Angstrom and 10,798 Angsrtom are among the most prominent lines in the near-infrared spectrum of the solar corona. They have been used routinely, both outside and during eclipses, as sensitive probes of the electron density and polarization in the solar corona. Many novae pass through a coronal phase, wherein the highly ionized nova ejecta have physical conditions that are remarkably similar to those of the solar corona. Many of the coronal emission lines that are seen are common to the spectra of both the Sun and novae. Yet, it appears that no robust detection of the [Fe XIII] lines has been made in a nova. Here we report the detection of these two infrared [Fe XIII]lines in the spectrum of the recurrent nova V3890 Sgr, taken 23.43 and 31.35 days after its August 2019 outburst. From their line strengths, we derive values of 10^10 per cubic cm and 10^[8.5-9] per cubic cm for the electron density on the two. The decrease in density between epochs can be explained if the density decreased with a power law n ~ r**alpha with a alpha inferred to be -3. The average temperature of the coronal gas is estimated to be T = (2.51\pm0.06) x 10^6~K. We find that recurrent novae with giant secondaries, including T CrB whose eruption is imminent, are the most suitable sources for further detections of the [Fe XIII] lines. epochs.