Near-infrared spectroscopy of the LMC recurrent nova LMCN 1968-12a

TL;DR

This study presents the first near-infrared spectra of an extragalactic nova, revealing extremely high coronal temperatures and unique spectral features during its eruption, providing new insights into nova physics.

Contribution

It provides the first near-infrared spectral analysis of an extragalactic nova and identifies exceptionally high coronal temperatures during eruption.

Findings

Detected the [SiX] 1.43μm line with high luminosity

Implied coronal temperatures exceeding 3 million Kelvin

Spectra lacked typical metal lines due to high ionization

Abstract

We have obtained near-infrared ($0.80-2.45\mu$m) spectra of the recurrent nova LMCN 1968-12a on two occasions during its 2024 August eruption. This is the first near-infrared spectroscopy of an extragalactic nova. The initial spectrum, on day 8.48, caught the nova in the coronal phase, with the [SiX] $1.43\mu$m line being extremely strong. This line had a luminosity of $\sim95$L$_\odot$, and is clearly a very powerful coolant. Its presence, together with the absence of [SiIX] 1.56$\mu$m, implies a coronal temperature $\gtrsim3\times10^6$K, possibly amongst the highest recorded coronal temperature in a nova eruption. With the exception of the [SiX] line, the near-infrared spectra are remarkable for being devoid of metal lines. We suggest that this is due, in part, to the exceptionally high temperature of the coronal gas, causing ions, whose emission lines would normally appear in the near-infrared spectrum, to be collisionally ionised to higher stages.