The secrets of T Pyxidis - II. A recurrent nova that will not become a SN Ia (original) (raw)

A&A 492, 787-803 (2008)

II. A recurrent nova that will not become a SN Ia

1 INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, Trieste, 34143 Trieste, Italy e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
2 INAF-IFSI, via del Fosso del Cavaliere 100, 00133 Roma, Italy, and Dipartimento di Fisica, Universita' Roma Tre, 00146 Roma, Italy
3 European Southern Observatory, Karl-Schwarzschild-Str 2, 85748 Garching bei München, Germany
4 XMM-Newton Science Operations Centre, ESAC, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain

Received: 25 July 2008
Accepted: 1 October 2008

Abstract

Aims. We compare the observed and theoretical parameters for the quiescent and outburst phases of the recurring nova T Pyx.

Methods. IUE data were used to derive the disk luminosity and the mass accretion rate, and to exclude the presence of quasi-steady burning at the WD surface. XMM-NEWTON data were used to verify this conclusion.

Results. By various methods, we obtained _L_disk ~ 70 $Mathematical equation: <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msub><mi>L</mi><mo lspace="0em" rspace="0em">⊙</mo></msub></mrow><annotation encoding="application/x-tex">L_{\odot}</annotation></semantics></math>L⊙$ and $Mathematical equation: <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mover accent="true"><mi>M</mi><mo>˙</mo></mover></mrow><annotation encoding="application/x-tex">\dot{M}</annotation></semantics></math>M˙$ ~ 1.1 $Mathematical equation: <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo>×</mo></mrow><annotation encoding="application/x-tex">\times</annotation></semantics></math>×$ 10 $Mathematical equation: <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msup><mrow></mrow><mrow><mo>−</mo><mn>8</mn></mrow></msup><mtext> </mtext><msub><mi>M</mi><mo lspace="0em" rspace="0em">⊙</mo></msub></mrow><annotation encoding="application/x-tex">^{-8}~M_{\odot}</annotation></semantics></math>−8 M⊙$ yr-1. These values were about twice as high in the pre-1966-outburst epoch. This allowed the first direct estimate of the total mass accreted before outburst, _M_accr = $Mathematical equation: <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msub><mover accent="true"><mi>M</mi><mo>˙</mo></mover><mrow><mi mathvariant="normal">p</mi><mi mathvariant="normal">r</mi><mi mathvariant="normal">e</mi><mo>−</mo><mi mathvariant="normal">O</mi><mi mathvariant="normal">B</mi></mrow></msub></mrow><annotation encoding="application/x-tex">\dot{M}_{\rm pre-OB}</annotation></semantics></math>M˙pre−OB$ $Mathematical equation: <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo>⋅</mo><mi mathvariant="normal">Δ</mi><mi>t</mi></mrow><annotation encoding="application/x-tex">\cdot \Delta t</annotation></semantics></math>⋅Δt$ , and its comparison with the critical ignition mass _M_ign. We found _M_accr and _M_ign to be in perfect agreement (with a value close to 5 $Mathematical equation: <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo>×</mo></mrow><annotation encoding="application/x-tex">\times</annotation></semantics></math>×$ 10 $Mathematical equation: <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msup><mrow></mrow><mrow><mo>−</mo><mn>7</mn></mrow></msup><mtext> </mtext><msub><mi>M</mi><mo lspace="0em" rspace="0em">⊙</mo></msub></mrow><annotation encoding="application/x-tex">^{-7}~M_{\odot}</annotation></semantics></math>−7 M⊙$ ) for _M_1 ~ 1.37 $Mathematical equation: <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msub><mi>M</mi><mo lspace="0em" rspace="0em">⊙</mo></msub></mrow><annotation encoding="application/x-tex">M_{\odot}</annotation></semantics></math>M⊙$ , which provides a confirmation of the thermonuclear runaway theory. The comparison of the observed parameters of the eruption phase, with the corresponding values in the grid of models by Yaron and collaborators, provides satisfactory agreement for values of _M_1 close to 1.35 $Mathematical equation: <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msub><mi>M</mi><mo lspace="0em" rspace="0em">⊙</mo></msub></mrow><annotation encoding="application/x-tex">M_{\odot}</annotation></semantics></math>M⊙$ and log $Mathematical equation: <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mover accent="true"><mi>M</mi><mo>˙</mo></mover></mrow><annotation encoding="application/x-tex">\dot{M}</annotation></semantics></math>M˙$ between -8.0 and -7.0, but the observed value of the decay time _t_3 is higher than expected. 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 $Mathematical equation: <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msup><mrow></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup><mtext> </mtext><msub><mi>M</mi><mo lspace="0em" rspace="0em">⊙</mo></msub></mrow><annotation encoding="application/x-tex">^{-4}~M_{\odot}</annotation></semantics></math>−4 M⊙$ . 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.

Key words: stars: novae, cataclysmic variables / stars: supernovae: general / X-rays: binaries / ultraviolet: general