Orbital Period Changes in Recurrent Nova T Corona Borealis Prove That It Is Not a Type Ia Supernovae Progenitor

Abstract

T Corona Borealis (T CrB) is a recurrent nova and a symbiotic star that is commonly highlighted as the best case for being a progenitor of a Type Ia supernova (SNIa) within the framework of single-degenerate models. This exemplar can be tested by measuring whether the white dwarf (WD) mass ($M_{\rm WD}$) is increasing over each eruption cycle. This is a balance between the mass ejected during each nova event ($M_{\rm ejecta}$) and the mass accreted onto the WD between the nova events ($M_{\rm accreted}$). I have used all 206 radial velocities from 1946--2024 to measure the orbital period just after the 1946 eruption to be $P_{\rm post}$=227.6043 days, while the steady orbital period change ($\dot{P}$) is ($-$3.1$\pm$1.6)$\times$10$^{-6}$. I have used my full 213,730 magnitude $B$ and $V$ light curve from 1842--2025 to measure the times of maximum brightness in the ellipsoidal modulations to construct the $O-C$ from 1866--1946. I fit the broken parabola shape, to find the orbital period immediately before the 1946 eruption to be $P_{\rm pre}$=227.4586 days. The orbital period changed by $\Delta P$=$+$0.146$\pm$0.019 days. With Kepler's Law, conservation of angular momentum, and the well-measured binary properties, the ejecta mass in 1946 is 0.00074$\pm$0.00009 M$_{\odot}$. $M_{\rm accreted}$ is reliably measured to be 1.38$\times$10$^{-6}$ M$_{\odot}$ from the accretion luminosity. $M_{\rm ejecta}$ is larger than $M_{\rm accreted}$ by 540$\times$, so $M_{\rm WD}$ is {\it decreasing} every eruption cycle. T CrB can never become a SNIa.