The Accelerating Decline of the Mass Transfer Rate in the Recurrent Nova T Pyxidis*

Abstract The recurrent nova T Pyxidis (T Pyx) has erupted six times since 1890, with its last outburst in 2011, and the relatively short recurrence time between classical nova explosions indicates that T Pyx must have a massive white dwarf (WD) accreting at a high rate. It is believed that, since its outburst in 1890, the mass transfer rate in T Pyx was very large due to a feedback loop where the secondary is heated by the hot WD. The feedback loop has been slowly shutting off, reducing the mass transfer rate, and thereby explaining the magnitude decline of T Pyx from ∼13.8 (before 1890) to 15.7 just before the 2011 eruption. We present an analysis of the latest Hubble Space Telescope far-ultraviolet and optical spectra, obtained 12 yr after the 2011 outburst, showing that the mass transfer rate has been steadily declining and is now below its preoutburst level by about 40%: <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> <mml:mo>∼</mml:mo> <mml:mn>1</mml:mn> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>7</mml:mn> </mml:mrow> </mml:msup> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> </mml:math> yr −1 for a WD mass of ∼1.0–1.4 M ⊙ , an inclination of 50°–60°, reddening of E ( B − V ) = 0.30 ± 0.05, and a Gaia Data Release 3 distance of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>2860</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>471</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>816</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> pc. This steady decrease in the mass transfer rate in the ∼decade after the 2011 outburst is in sharp contrast with the more constant preoutburst ultraviolet continuum flux level from archival International Ultraviolet Explorer spectra. The flux (i.e., <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> </mml:math> ) decline rate is 29 times faster now in the last ∼decade than observed since 1890 to ∼2010. The feedback loop shut off seems to be accelerating, at least in the decade following its 2011 outburst. In all eventualities, our analysis confirms that T Pyx is going through an unusually peculiar short-lived phase.