An international team of astronomers has leveraged NASA’s Transiting Exoplanet Survey Satellite (TESS) to scrutinize the outburst of Nova Vulpeculae 2021. Their findings, disclosed on November 8 via the arXiv pre-print server, unveil crucial insights into the distinctive nature of this classical nova, exposing intricate variability patterns.
Classical novae involve stars undergoing a sudden brightness surge followed by a gradual return to their initial state, a process spanning several months. This phenomenon stems from the accretion process within a tight binary system comprising a white dwarf (WD) and its companion.
While typical novae follow a rapid brightness ascent and a smooth decline, Nova Vulpeculae 2021 (or V606 Vul) diverges from this standard model. Discovered on July 16, 2021, nine days before TESS observations commenced, V606 Vul prompted astronomers, led by Kirill Sokolovsky from the University of Illinois at Urbana-Champaign, to delve into its complexities using TESS.
“We use TESS photometry of the V606 Vul eruption to characterize variability of a nova in exquisite detail,” state the researchers in their paper.
TESS observations covered the first of two primary peaks post the eruption, revealing that the nova reached its maximum visual magnitude during the second peak, occurring 64 days later.
Examining the light curve, the team identified periodic variations with a roughly 3.06-hour cycle and an average peak-to-peak amplitude of 0.01 mag, except when the nova approached peak brightness. Mini-flares, featuring peak-to-peak amplitudes up to 0.5 mag, appeared randomly, interspersed with undisturbed periodic variations.
The periodic variations vanished at the peak brightness, leading astronomers to propose an azimuthal asymmetry of the photosphere in the underlying binary system as the cause. However, alternative explanations, such as temperature-based azimuthal asymmetry, are not ruled out.
In summary, the paper’s authors highlight the pioneering use of TESS photometry in exploring nova eruptions, emphasizing TESS’s precision for detecting low-amplitude brightness variations and its capability for uninterrupted month-long observations, enabling exploration of variability on a 12–24-hour timescale challenging for ground-based observations interrupted by diurnal cycles.