Abstract
Abstract 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 × 10 − 3 M ⊙. 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 105.57±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.
Highlights
Classical nova (CN) systems consist of a semi-detached binary containing a white dwarf (WD) and a Roche-lobe-filling secondary star, usually a late-type dwarf
We present near infrared spectroscopy of Nova Herculis 2021 (V1674 Her), obtained over the first 70 days of its evolution
We show that the vexing problem of whether collisional 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
Summary
Classical nova (CN) systems consist of a semi-detached binary containing a white dwarf (WD) and a Roche-lobe-filling secondary star, usually a late-type dwarf. Material from the secondary spills on to the surface of the WD through the inner Lagrangian point, via an accretion disk. The material at the base of the accreted envelope becomes degenerate, triggering a thermonuclear runaway (TNR; for a review see Bode & Evans 2012; Starrfield et al 2020). There is a relation between the absolute magnitude at maximum and the rate of the light curve decline, the “MMRD” relation (see Della Valle & Izzo 2020, and references therein). These relationships are likely a consequence of the mass of the WD on which the TNR occurred (Starrfield et al 2020)
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