Novae heat their food: mass transfer by irradiation. (arXiv:2104.11250v1 [astro-ph.SR])

Novae heat their food: mass transfer by irradiation. (arXiv:2104.11250v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ginzburg_S/0/1/0/all/0/1">Sivan Ginzburg</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Quataert_E/0/1/0/all/0/1">Eliot Quataert</a>

A nova eruption irradiates and heats the donor star in a cataclysmic variable
to high temperatures $T_{rm irr}$, causing its outer layers to expand and
overflow the Roche lobe. We calculate the donor’s heating and expansion both
analytically and numerically and find that irradiation drives enhanced mass
transfer from the donor at a rate $dot{m}propto T_{rm irr}^{5/3}$, which
reaches $dot{m}sim 10^{-6}textrm{ M}_odottextrm{ yr}^{-1}$ 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 $dot{m}sim 10^{-7}textrm{
M}_odottextrm{ yr}^{-1}$ 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.

A nova eruption irradiates and heats the donor star in a cataclysmic variable
to high temperatures $T_{rm irr}$, causing its outer layers to expand and
overflow the Roche lobe. We calculate the donor’s heating and expansion both
analytically and numerically and find that irradiation drives enhanced mass
transfer from the donor at a rate $dot{m}propto T_{rm irr}^{5/3}$, which
reaches $dot{m}sim 10^{-6}textrm{ M}_odottextrm{ yr}^{-1}$ 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 $dot{m}sim 10^{-7}textrm{
M}_odottextrm{ yr}^{-1}$ 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.

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