Orbital Period Changes of Recurrent Nova T Pyxidis Demonstrate that M_ejecta >> 11.3xM_accreted and Is Not a Type Ia Supernova Progenitor

TL;DR

This study uses a robust dynamical approach to resolve whether the recurrent nova T Pyxidis can become a Type Ia supernova by directly comparing total mass ejected per eruption cycle with total mass accreted. By measuring the orbital-period change $\Delta P$ across the 2011 eruption and combining it with a carefully reconstructed accretion history (informed by a long, multi-decade photometric record and the system’s spectral energy distribution), the paper derives a strict lower limit on $M_{ m ejecta}$ and a best estimate for $M_{ m ejecta}$ that far exceeds $M_{ m accreted}$, yielding $M_{ m ejecta} \gg 11.3\times M_{ m accreted}$. The inferred full-cycle budgets give $M_{ m accreted}\approx 220\times10^{-7}\,M_{\odot}$ and $M_{ m ejecta}>17120\times10^{-7}\,M_{\odot}$, implying the white dwarf is losing mass and cannot reach the Chandrasekhar mass. The result, reinforcing a growing suite of studies, demonstrates that certain popular SNIa progenitor channels are not viable and provides a powerful, distance-independent, and model-insensitive method to quantify nova mass budgets with broad implications for binary evolution and supernova progenitor demographics.

Abstract

Recurrent nova (RN) T Pyxidis (T Pyx) has a complex history of mass accreting-onto and ejection-from the white dwarf, with a classical nova eruption around 1866 kick-starting a RN-phase with six RN eruptions from 1890--2011. T Pyx is a primary progenitor candidate for Type Ia supernovae (SNIa). This is chiefly a question of whether the mass accreted by the white dwarf ($M_{\rm accreted}$) is more-or-less than the mass ejected by the nova eruptions ($M_{\rm ejecta}$) over the entire eruption cycle. Prior attempts to measure $M_{\rm ejecta}$ from the traditional methods have a scatter of $>$130$\times$, so only a new technique can provide a measure of adequate accuracy and reliability. This new technique is the timing experiment of measuring the orbital period from 1986 to 2025, where the period increased by $+$50.3$\pm$7.9 parts-per-million across the 2011 eruption. With simple and sure physics, the best estimate for the mass ejected by one RN event is $>$2400$\times$10$^{-7}$ M$_{\odot}$, with an extreme inviolate limit of $\gg$354$\times$10$^{-7}$ M$_{\odot}$. Over all eruptions in a cycle, $M_{ejecta}$$>$17120$\times$10$^{-7}$ M$_{\odot}$, with an inviolate limit of $M_{ejecta}$$\gg$2144$\times$10$^{-7}$ M$_{\odot}$. Over the full eruption cycle, the white dwarf accreted 220$\times$10$^{-7}$ M$_{\odot}$. So M$_{\rm ejecta}$$\gg$11.3$\times$M$_{\rm accreted}$, and T Pyx can never become a SNIa. This paper is the seventh in a series proving that each of various popular candidate SNIa progenitors cannot possibly evolve to a supernova; including V445 Pup, U Sco, T CrB, all symbiotic stars, FQ Cir, V1405 Cas, and now T Pyx.

Figures (4)

• Figure 1: T Pyx yearly-averaged $B$ light curve. This was constructed from 30,445 magnitudes, covering from before the 1890 eruption until near the end of 2025. Importantly, we see T Pyx declines from $B$=13.95 in early 1890 to $B$=16.06 in 2025 (a factor of 7.0$\times$ change in flux). This shows the slow decline of the extreme-high-accretion RN-phase (kicked off by the 1866 classical nova eruption) of the millennia-long T Pyx eruption cycle.
• Figure 2: T Pyx accretion rate from 1800 to 2200. The whole eruption cycle consists of an RN-phase alternating with a long quiescent phase. The quiescent phase lasts perhaps 13,000 years, during which the WD accumulates gas slowly with a low-$\dot{M}$, as appropriate for T Pyx being under the Period Gap. Around the year 1866, the gas accumulating on the WD reached the trigger mass, and the classical nova eruption ejects $\sim$10$^{-4.5}$$M_{\odot}$ with velocities 500--715 km/s, as shown with the orange star. For some reason (likely due to continued nuclear burning on the WD surface irradiating and bloating the companion star's atmosphere), the classical nova event drives extremely high $\dot{M}$. The resultant high accretion rate starts a recurrent nova phase that lasts more than two centuries. Throughout the RN-phase, we have been watching the accretion falling off (see Figure 1), as the feedback loop weakens. This unique secular decline in $\dot{M}$ make the star's brightness fade and the time between RN eruptions (the red stars) increase from 12 years to 44 years. The RN-phase has 6 observed RN events 1890--2011, plus another likely RN around 1883, indicated by the red stars. For the future, presumably the $\dot{M}$ will keep fading at the 2011--2025 observed rate of 0.044 mag/year, with the extrapolated decline indicated by the dotted line. After 2011, with any plausible decline rate, T Pyx will not accumulate the trigger mass until many millennia from now, so there will be no further RN eruptions in the current RN-phase. While the uncertainty is large, T Pyx will return to it normal quiescent level sometime around the year 2137. Then, it will take another 12,800 years or so to accumulate enough gas on the WD to trigger another classical nova eruption, to start the entire eruption cycle again.
• Figure 3: TESS folded and phase-averaged light curves. The light curves show an ordinary CV, with the broad minimum at the time when the radial velocity curve has the companion star exactly in front of the WD. Nevertheless, the primary minimum cannot be from an eclipse, because the total duration of the minimum is nearly 0.5 in phase.
• Figure 4: $O-C$ curve for T Pyx. This plot has 131 times of minimum (red diamonds) from 1986 to 2025, with the ephemeris having period 0.07622916 days and epoch HJD 2455665.9962. The best-fit broken parabola is shown with the black curve, which is a remarkably good match to the observed times. The main point of this figure is that T Pyx had a sharp upward kink at the time of the 2011 eruption (denoted by the blue vertical line), which shows that the orbital period increased by $+$50.3$\pm$7.9 parts-per-million. This is the long and hard result that provides a strict lower limit on the mass ejected during the 2011 eruption. A further important point is that the kink is at 108.4$\pm$12.6 days after the start of the eruption (see inset). This means that the median ejection was late in the eruption, and the mass ejection continued for hundreds of days. This disproves the old standard idea that the ejections are some optically thick wind blasted off by the original thermonuclear runaway, and rather that the ejections are driven by the companion orbiting within the hot envelope surrounding the WD. A third important point from this figure is that the very well-measured $\dot{P}$ (shown by the parabolic curvature) is large-and-positive before 2011, and much smaller and positive after the 2011 eruption. Something about the nova eruption changed the state of the binary for at least the next 15 years of quiescence, with the obvious mechanism being that the large mass ejection enlarged the binary orbit so that the Roche lobe rises in the companion's atmosphere, which lowers the $\dot{M}$ and decreases the $\dot{P}$. A fourth point is that the $\dot{P}$ values are positive, and this is impossible in the Magnetic Braking Model for CV evolution (Knigge et al. 2011), with this being just one of many counterexamples (Schaefer 2024; 2025b). A fifth point is that the T Pyx evolution has the period increasing from beginning-to-end, contrary to the pervasive idea that all CVs evolve from long-$P$ to short-$P$. This case is just one counterexample out of many, where roughly half of all CVs and XRBs have their periods increasing over the entire observed range (Schaefer 2024; 2025b). This sampling of 77 systems disproves the ubiquitous ideal that all CVs and XRBs evolve from long-period to short-period.