Proper-motion age dating of the progeny of Nova Scorpii AD 1437

• Published in: Nature (London) Vol. 548; no. 7669; pp. 558 - 560
• Main Authors: Shara, M. M., Iłkiewicz, K., Mikołajewska, J., Pagnotta, A., Bode, M. F., Crause, L. A., Drozd, K., Faherty, J., Fuentes-Morales, I., Grindlay, J. E., Moffat, A. F. J., Pretorius, M. L., Schmidtobreick, L., Stephenson, F. R., Tappert, C., Zurek, D.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 31.08.2017; Nature Publishing Group
• Subjects: 639/33/34/865; 639/33/34/867; Accretion; Accretion disks; Astronomy; Binary stars; Brightening; Cataclysmic variables; Companion stars; Dating techniques; Dwarf novae; Humanities and Social Sciences; Hydrogen; letter; Mass transfer; multidisciplinary; Novae; Observations; Orbits; Outbursts; Proper motion; Science; Stars; Stars & galaxies; Stellar systems; Telescopes; White dwarf stars
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature23644

The re-discovery of the binary star system that created the Nova Scorpii AD 1437 stellar outburst shows that it is now a dwarf nova, suggesting that nova systems spend some time as dwarf novae in between larger outbursts. Scorpii exploded from a dwarf nova Novae occur in binary star systems with a white dwarf and a very close red dwarf. Gas from the red dwarf is accreted onto the white dwarf and occasionally 'explodes' in a thermonuclear runaway that increases the luminosity of the system to up to a million solar luminosities. Binaries known as dwarf novae, which otherwise look like the nova binaries, have more frequent, but much smaller explosions. Michael Shara and colleagues have tracked down the binary system that created the Nova Scorpii AD 1437 explosion, and find that it is now a dwarf nova. They conclude that nova systems spend some time as dwarf novae in between the larger outbursts. ‘Cataclysmic variables’ are binary star systems in which one star of the pair is a white dwarf, and which often generate bright and energetic stellar outbursts. Classical novae are one type of outburst: when the white dwarf accretes enough matter from its companion, the resulting hydrogen-rich atmospheric envelope can host a runaway thermonuclear reaction that generates a rapid brightening 1 , 2 , 3 , 4 . Achieving peak luminosities of up to one million times that of the Sun 5 , all classical novae are recurrent, on timescales of months 6 to millennia 7 . During the century before and after an eruption, the ‘novalike’ binary systems that give rise to classical novae exhibit high rates of mass transfer to their white dwarfs 8 . Another type of outburst is the dwarf nova: these occur in binaries that have stellar masses and periods indistinguishable from those of novalikes 9 but much lower mass-transfer rates 10 , when accretion-disk instabilities 11 drop matter onto the white dwarfs. The co-existence at the same orbital period of novalike binaries and dwarf novae—which are identical but for their widely varying accretion rates—has been a longstanding puzzle 9 . Here we report the recovery of the binary star underlying the classical nova eruption of 11 March AD 1437 (refs 12 , 13 ), and independently confirm its age by proper-motion dating. We show that, almost 500 years after a classical-nova event, the system exhibited dwarf-nova eruptions. The three other oldest recovered classical novae 14 , 15 , 16 display nova shells, but lack firm post-eruption ages 17 , 18 , and are also dwarf novae at present. We conclude that many old novae become dwarf novae for part of the millennia between successive nova eruptions 19 , 20 .