Novae heat their food: mass transfer by irradiation

Abstract

A nova eruption irradiates and heats the donor star in a cataclysmic variable to high temperatures $T_{\mathrm{irr}}$, causing its outer layers to expand and overflow the Roche lobe. We calculate the donor's heating and expansion both analytically and numerically, under the assumption of spherical symmetry, and find that irradiation drives enhanced mass transfer from the donor at a rate $\dot{m}\propto T_{\mathrm{irr}}^{5/3}$, which reaches $\dot{m}\sim 10^{-6}{\text{ M}}_{\odot }{\text{ yr}}^{-1}$ at the peak of the eruption - about a thousand times faster than during quiescence. As the nova subsides and the white dwarf cools down, $\dot{m}$ drops to lower values. We find that under certain circumstances, the decline halts and the mass transfer persists at a self-sustaining rate of $\dot{m}\sim 10^{-7}{\text{ M}}_{\odot }{\text{ yr}}^{-1}$ for up to $\sim 10^3$ yr after the eruption. At this rate, irradiation by the white dwarf's accretion luminosity is sufficient to drive the mass transfer on its own. The self-sustaining rate is close to the white dwarf's stable burning limit, such that this bootstrapping mechanism can simultaneously explain two classes of puzzling binary systems: recurrent novae with orbital periods $\approx 2$ h (T Pyxidis and IM Normae) and long-lived supersoft X-ray sources with periods $\approx 4$ h (RX J0537.7-7034 and 1E 0035.4-7230). Whether or not a system reaches the self-sustaining state is sensitive to the donor's chromosphere structure, as well as to the orbital period change during nova eruptions.

Matches published version: added order-unity coefficients, a more detailed comparison with previous calculations, and some discussion

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• Binary Interaction Dominates Mass Ejection in Classical Novae
• The first nova eruption in a novalike variable: YZ Ret as seen in X-rays and gamma-rays
• Transients from the Cataclysmic Deaths of Cataclysmic Variables
• Gamma-Ray Light Curves and Spectra of Classical Novae
• 1RXH J082623.6-505741: a new long-period cataclysmic variable with an evolved donor and a low mass transfer rate
• Short Duration Accretion States of Polars as seen in TESS and ZTF data
• The activity of the post-nova V1363 Cyg on long timescales
• V1047 Cen: The first Z And-type outburst observed in the classical nova binary
• The Periodic Signals of Nova V1674 Herculis (2021)
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