Abstract
Abstract Nova eruptions, thermonuclear explosions on the surfaces of white dwarfs (WDs), are now recognized to be among the most common shock-powered astrophysical transients. We present the early discovery and rapid ultraviolet (UV), optical, and infrared (IR) temporal development of AT 2019qyl, a recent nova in the nearby Sculptor Group galaxy NGC 300. The light curve shows a rapid rise lasting ≲1 day, reaching a peak absolute magnitude of M V = −9.2 mag and a very fast decline, fading by 2 mag over 3.5 days. A steep dropoff in the light curves after 71 days and the rapid decline timescale suggest a low-mass ejection from a massive WD with M WD ≳ 1.2 M ⊙. We present an unprecedented view of the early spectroscopic evolution of such an event. Three spectra prior to the peak reveal a complex, multicomponent outflow giving rise to internal collisions and shocks in the ejecta of an He/N-class nova. We identify a coincident IR-variable counterpart in the extensive preeruption coverage of the transient location and infer the presence of a symbiotic progenitor system with an O-rich asymptotic-giant-branch donor star, as well as evidence for an earlier UV-bright outburst in 2014. We suggest that AT 2019qyl is analogous to the subset of Galactic recurrent novae with red-giant companions such as RS Oph and other embedded nova systems like V407 Cyg. Our observations provide new evidence that internal shocks between multiple, distinct outflow components likely contribute to the generation of the shock-powered emission from such systems.
Highlights
Novae are a class of cataclysmic variables (CVs) whose eruptions are the result of a thermonuclear runaway (TNR) on the surface of a white dwarf (WD) accreting hydrogen-rich material from a nondegenerate companion (Gallagher & Starrfield 1978)
By the continued nuclear burning, used as a proxy for the WD mass (e.g., Henze et al 2011; Schwarz et al 2011; Wolf et al 2013). We show their predicted power laws in comparison to our light curves in Figure 2, and, while the measured power-law indices for t > 10 days (α2 in Table 3) do not precisely match the predicted value, we note a qualitative similarity between the predictions and the observed slowdecline phase and subsequent dropoff
We have described the early discovery and prompt follow-up observations of AT 2019qyl, a very fast nova with an O-rich AGB donor in NGC 300
Summary
Novae are a class of cataclysmic variables (CVs) whose eruptions are the result of a thermonuclear runaway (TNR) on the surface of a white dwarf (WD) accreting hydrogen-rich material from a nondegenerate companion (Gallagher & Starrfield 1978). Aydi et al (2020a) revisited this topic with a sample of premaximum spectra of 12 novae, all showing consistent evidence for distinct velocity components in their ejecta This scenario is expected to invariably give rise to shocks (McLaughlin 1947; Friedjung 1987, 2011; Friedjung & Duerbeck 1993) and provides important clues on the yet poorly understood mass-loss mechanisms that may operate in nova eruptions. High-cadence transient surveys are well equipped to discover fast and faint transients in galaxies beyond the Local Group and offer the most expedient route to obtaining the early (within hours of eruption) observations necessary to probe the outflow structure and massloss mechanisms of embedded RG novae and rapidly evolving, extragalactic analogs to RNe in the Milky Way. Here we present the discovery of the recent nova AT 2019qyl in the nearby Sculptor Group galaxy NGC 300 and identify its luminous RG counterpart.
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