Nova Ophiuchus 2017 as a probe of $^{13}$C nucleosynthesis and carbon monoxide formation and destruction in classical novae

TL;DR

This study provides detailed near-infrared spectral observations of Nova Ophiuchus 2017, tracking CO emission evolution, analyzing destruction mechanisms, and determining the $^{12}$C/$^{13}$C ratio, which aligns with nucleosynthesis predictions for low-mass white dwarf novae.

Contribution

It offers the first detailed temporal analysis of CO emission in a nova and securely measures the $^{12}$C/$^{13}$C ratio, linking observations to nucleosynthesis models.

Findings

CO emission declines rapidly within 25 days post-maximum

$^{12}$C/$^{13}$C ratio is 1.6 ± 0.3, consistent with low-mass white dwarf models

Multiple mechanisms for CO destruction are considered and analyzed

Abstract

We present a series of near-infrared spectra of Nova Ophiuchus 2017 in the $K$ band that record the evolution of the first overtone CO emission in unprecedented detail. Starting from 11.7d after maximum, when CO is first detected at great strength, the spectra track the CO emission to +25.6d by which time it is found to have rapidly declined in strength by almost a factor of $\sim$ 35. The cause for the rapid destruction of CO is examined in the framework of different mechanisms for CO destruction viz. an increase in photoionizating flux, chemical pathways of destruction or destruction by energetic non-thermal particles created in shocks. From LTE modelling of the CO emission, the $^{12}$C/$^{13}$C ratio is determined to be 1.6 $\pm$ 0.3. This is consistent with the expected value of this parameter from nucleosynthesis theory for a nova eruption occuring on a low mass ($\sim$ 0.6 M$_\odot$) carbon-oxygen core white dwarf. The present $^{12}$C/$^{13}$C estimate constitutes one of the most secure estimates of this ratio in a classical nova.