Fate and detectability of rare gas hydride ions in nova ejecta: A case study with nova templates

TL;DR

This study models the formation and potential detectability of noble gas hydride ions, especially HeH$^+$, in nova ejecta, suggesting JWST could observe these molecules in certain nova environments to inform physical conditions.

Contribution

It provides the first detailed photoionization models of noble gas hydride ions in nova ejecta, predicting their formation and observability with JWST, using nova templates.

Findings

HeH$^+$ can form in dense nova ejecta regions.

JWST could detect HeH$^+$ lines in certain nova remnants.

Models predict observable HeH$^+$ transitions in specific nova environments.

Abstract

HeH$^+$ was the first heteronuclear molecule to form in the metal-free Universe after the Big Bang. The molecule gained significant attention following its first circumstellar detection in the young and dense planetary nebula NGC 7027. We target some hydride ions associated with the noble gases (HeH$^+$, ArH$^+$, and NeH$^+$) to investigate their formation in harsh environments like the nova outburst region. We use a photoionization modeling (based on previously published best-fit physical parameters) of the moderately fast ONe type nova, QU Vulpeculae 1984, and the CO type novae, RS Ophiuchi and V1716 Scorpii. Our steady-state modeling reveals a convincing amount of HeH$^+$, especially in the dense clump of RS Ophiuchi and V1716 Scorpii. The calculated upper limit on the surface brightness of HeH$^+$ transitions suggests that the James Webb Space Telescope (JWST) could detect some of them, particularly in sources like RS Ophiuchi and V1716 Scorpii, which have similar physical and chemical conditions and evolution. It must be clearly noted that the sources studied are used as templates, and not as targets for observations. The detection of these lines could be useful for determining the physical conditions in similar types of systems and for validating our predictions based on new electron-impact ro-vibrational collisional data at temperatures of up to 20,000 K.