Near-infrared spectroscopy of RS Ophiuchi in 2021: the calm, the storm, and the abatement

TL;DR

This study presents detailed near-infrared observations of RS Ophiuchi's 2021 eruption, revealing spectral evolution, coronal gas properties, and potential secondary star changes, enhancing understanding of recurrent nova eruptions.

Contribution

It provides high-cadence NIR spectra during the eruption and pre-eruption spectra, offering new insights into the spectral evolution and coronal gas conditions of RS Ophiuchi.

Findings

Coronal gas temperature estimated at 10^6 K during eruption

No rapid variations detected in HeI 1.0833 μm line

Possible spectral type change of secondary star post-eruption

Abstract

We present near-infrared (NIR) observations of the 2021 eruption of the recurrent nova RS Ophiuchi. The dataset provides both pre- and post-eruption perspectives on the eruption, as well as NIR spectra at high cadence. The spectrum obtained in 2020 June (14.3 years after the 2006 eruption, and 428.1 days before the 2021 eruption), is that of the red giant secondary, on which are superimposed several emission lines which most likely arise in the red giant wind. Spectra obtained during the eruption consist of emission (including coronal) lines, superimposed on a bremsstrahlung continuum at 8900K. The temperature of the coronal gas is estimated to be $10^{6.0}$K on day 11.7, and $10^{5.9}$K on day 31.7. The high cadence observations, obtained on day 31.7 of the eruption, provide no conclusive evidence for rapid ($<\sim1$~minute) variations in the HeI 1.0833$\,\mu$m line. Data obtained about one year after the eruption show that there may have been changes in the spectral type of the secondary after the 2021 eruption.