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NOVAE WITH LONG-LASTING SUPERSOFT EMISSION THAT DRIVE A HIGH ACCRETION RATE

机译:NOVAE WITH LONG-LASTING SUPERSOFT EMISSION THAT DRIVE A HIGH ACCRETION RATE

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摘要

We identify a new class of novae characterized by the post-eruption quiescent light curve being more than roughlya factor of 10 brighter than the pre-eruption light curve. Eight novae (V723 Cas, V1500 Cyg, V1974 Cyg, GQ Mus,CP Pup, T Pyx, V4633 Sgr, and RW UMi) are separated out as being significantly distinct from other novae. Thisgroup shares a suite of uncommon properties, characterized by the post-eruption magnitude being much brighterthan before eruption, short orbital periods, long-lasting supersoft emission following the eruption, a highly magnetizedwhite dwarf (WD), and secular declines during the post-eruption quiescence. We present a basic physicalpicture which shows why all five uncommon properties are causally connected. In general, novae show supersoftemission due to hydrogen burning on the WD in the final portion of the eruption, and this hydrogen burning willbe long-lasting if new hydrogen is poured onto the surface at a sufficient rate. Most novae do not have adequateaccretion for continuous hydrogen burning, but some can achieve this if the companion star is nearby (with shortorbital period) and a magnetic field channels the matter onto a small area on the WD so as to produce a locallyhigh accretion rate. The resultant supersoft flux irradiates the companion star and drives a higher accretion rate(with a brighter post-eruption phase), which serves to keep the hydrogen burning and the supersoft flux going. Thefeedback loop cannot be perfectly self-sustaining, so the supersoft flux will decline over time, forcing a decline inthe accretion rate and the system brightness. We name this new group after the prototype, V1500 Cyg. V1500 Cygstars are definitely not progenitors of Type Ia supernovae. The V1500 Cyg stars have similar physical mechanismsand appearances as predicted for nova by the hibernation model, but with this group accounting for only 14 ofnovae.

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