Letter to the Editor

A very rapidly rotating white dwarf in nova YZ Reticuli

¹ Universidad Nacional de Hurlingham (UNAHUR). Laboratorio de Investigación y Desarrollo Experimental en Computación, Grupo de Astrofísica, Av. Gdor. Vergara 2222, Villa Tesei, Buenos Aires, Argentina
² Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
³ South African Astronomical Observatory, PO Box 9 Observatory, Cape Town, 7935, South Africa
⁴ International Gemini Observatory/NSF NOIRLab, Casilla 603, La Serena, Chile
⁵ INAF-Osservatorio Astronomico di Padova, vicolo Osservatorio, 5, 35122 Padova, Italy
⁶ Department of Astronomy, University of Wisconsin, 475 N. Charter Str., Madison WI 53706, WI, USA
⁷ Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
⁸ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80131 Naples, Italy
⁹ Advanced Technologies Research Institute, Faculty of Materials Science and Technology in Trnava, Slovak University of Technology in Bratislava, Bottova 25, 917 24 Trnava, Slovakia

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 15 May 2026
Accepted: 4 July 2026

Abstract

YZ Ret (Nova Reticuli 2020) is the first VY Scl-type nova-like variable observed to have undergone a classical nova eruption. Following the outburst, a timing analysis of 20-s cadence TESS data revealed a periodicity at approximately 42 s, suggesting its plausible classification as a fast-spinning intermediate polar (IP). To definitively identify the nature of this modulation, we performed a multi-instrument timing analysis using high-speed ground-based photometry Zorro/Gemini South (1 s cadence) and the South African Astronomical Observatory (5 s cadence) alongside TESS Sector 97 observations. Our ground-based data reveal a highly coherent period of 37.69131 ± 0.00001 s, which we identified as the true rotation period of the white dwarf. We demonstrate that the apparent 42.61 s signal in the TESS data is a Nyquist alias of this fundamental frequency. Furthermore, the signal amplitude in the TESS data is suppressed by a factor of ≈0.6 relative to the Gemini observations, a result that is consistent with the theoretical sinc-function damping expected for a 20-s integration time. The extreme coherence and long-term stability of the 37.69131 s signal rule out transient phenomena such as dwarf nova oscillations or non-radial pulsations. We conclude that YZ Ret hosts a fast-spinning magnetic white dwarf in an IP configuration. This discovery implies that mass loss during the nova eruption was likely driven by a fast magnetic rotator wind and provides a physical explanation for the missing supersoft X-ray phase, suggesting that nearly the entire accreted envelope was exhausted, promptly quenching the process of nuclear burning.