UV and X-ray observations of T Pyx, a recurrent nova that will not become a SN Ia

We have accurately determined, from UV and other observations, the accretion disk luminosity of T Pyx during both the pre- and post-1966 inter-outburst phases. For M_1 ∼ 1.37 M_⊙, we have found that dot {M}_pre-OB ∼ 2.2 × 10^-8 M_⊙ yr^-1. By combining the measured accretion rate with the duration of the inter-outburst phase (Delta t = 22 yrs), the total accreted mass is inferred to be M_accr=dot {M}_pre-OB * Delta t ∼ 5.2 × 10^-7 M_⊙. This value is in excellent agreement with the theoretical ignition mass (M_ign) ∼ 5.0 × 10^-7M_⊙ expected for a massive white dwarf accreting at the quoted rate. However, the long duration of the optically thick phase during the recorded outbursts of T Pyx, a spectroscopic behavior typical of classical novae, and the persistence of P Cyg profiles, constrains the ejected mass M_ign to within 10^-5 - 10^-4 M_⊙. Therefore, T Pyx ejects far more material than it has accreted, and the mass of the white dwarf will not increase to the Chandrasekhar limit as generally believed in recurrent novae. A detailed study based on the UV data excludes the possibility that T Pyx belongs to the class of the supersoft X-ray sources, as has been postulated. XMM-NEWTON observations have revealed a weak, hard source and confirmed this interpretation.