A TESS View of Post-Eruption Variability in the Novae V1405 Cas,V1716 Sco, and V1674 Her

TL;DR

This study uses TESS data to analyze post-eruption variability in three novae, revealing rapid white dwarf spin-down, new orbital periods, and insights into magnetic states and accretion processes.

Contribution

First detailed TESS analysis of post-eruption white dwarf periods in multiple novae, uncovering rapid spin-down and challenging existing models of cataclysmic variable evolution.

Findings

V1405 Cas exhibits a rapid WD spin-down rate of 0.00165 s/d.

V1716 Sco has a newly measured orbital period of 1.357 days.

V1674 Her's known spin and orbital periods are confirmed, with implications for X-ray modulation.

Abstract

We analyzed TESS archival data of three novae after recent outbursts, searching the orbital and white dwarf (WD) rotation period and possible variations of these periods. In V1405 Cas, we detected a period of $\sim$116.88 seconds, which we identified as due to the WD spin, and measured a rate of increase of 0.00165$\pm0.000006\, {\rm s\, d}^{-1}$, one of the fastest spin-down rates ever recorded. The rapid spin-down coupled with an X-ray luminosity several orders of magnitude lower than the available spin-down power, strongly indicates that the system is in a magnetic ``propeller'' state, namely the rotational energy powers the system's X-ray luminosity. We measured a previously unknown orbital period of 1.357$\pm0.005\,{\rm days}$ for V1716 Sco. If the X-ray flux modulation with a period of 77.9 s detected in outburst for this nova is due to the rotation of an strongly magnetized white dwarf as in other novae with similar modulations of the supersoft X-ray source in outburst, the system is in a parameter space that challenges standard models of cataclysmic variable evolution. For V1674 Her, which has already been classified as an intermediate polar (IP), we confirm the known spin period of 501.328$\pm0.024\,{\rm s}$ and the orbital period of $0.15293 \pm 0.00004$ days, suggesting that the spin modulation was also the root cause of the periodicity in X-rays in outburst, and that the WD atmosphere in the supersoft X-ray phase was not thermally homogeneous. Our results highlight the power of high-cadence, continuous observations in revealing extreme and unexpected characteristics of accreting white dwarfs.