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 (SN Ia) within the framework of single-degenerate models. This exemplar can be tested by measuring whether the white dwarf (WD) mass ( M WD ) is increasing over each eruption cycle. This is a balance between the mass ejected during each nova event ( M ejecta ) and the mass accreted onto the WD between the nova events ( M accreted ). I have used all 206 radial velocities from 1946 to 2024 to measure the orbital period just after the 1946 eruption, which is P post = 227.6043 days, while the steady orbital period change ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> </mml:math> ) is (−3.1 ± 1.6) × 10 −6 . I have used my full 213,730 magnitude B and V light curve from 1842 to 2025 to measure the times of maximum brightness in the ellipsoidal modulations to construct the O − C from 1866 to 1946. I fit the broken parabola shape to find the orbital period immediately before the 1946 eruption, which is <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">pre</mml:mi> </mml:mrow> </mml:msub> </mml:math> = 227.4586 days. The orbital period changed by Δ P = +0.146 ± 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 ± 0.00009 M ⊙ . M accreted is reliably measured to be 1.38 × 10 −6 M ⊙ from the accretion luminosity. M ejecta is larger than M accreted by 540×, so M WD is decreasing every eruption cycle. T CrB can never become an SN Ia.