Near-infrared Studies of Nova V1674 Herculis: A Shocking Record Breaker

We present near-infrared spectroscopy of Nova Herculis 2021 (V1674 Her), obtained over the first 70 days of its evolution. This fastest nova on record displays a rich emission line spectrum, including strong coronal line emission with complex structures. The hydrogen line fluxes, combined with a distance of 4.7(-1.0)(+1.3) kpc, give an upper limit to the hydrogen ejected mass of M-ej = 1.4(-1.2)(+0.8) x 10(-3) M-circle dot. The coronal lines appeared at day 11.5, the earliest onset yet observed for any classical nova, before there was an obvious source of ionizing radiation. We argue that the gas cannot be photoionized, at least in the earliest phase, and must be shocked. Its temperature is estimated to be 10(5.57 +/- 0.05) K on day 11.5. Tentative analysis indicates a solar abundance of aluminum and an underabundance of calcium, relative to silicon, with respect to solar values in the ejecta. Further, we show that the vexing problem of whether collisional ionization or photoionization is responsible for coronal emission in classical novae can be resolved by correlating the temporal sequence in which the X-ray supersoft phase and the near-infrared coronal line emission appear.

Automated summary

This study presents near-infrared spectroscopy of Nova Herculis 2021, revealing a rich emission line spectrum with strong coronal line emissions. The hydrogen ejected mass is estimated to have an upper limit of 1.4 x 10(-3) solar masses, and coronal lines appeared at day 11.5, the earliest onset observed for any classical nova. The vexing problem of whether collisional ionization or photoionization is responsible for coronal emission in classical novae can be resolved by correlating the temporal sequence of X-ray supersoft phase and near-infrared coronal line emission.