‘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 brightening1,2,3,4. Achieving peak luminosities of up to one million times that of the Sun5, all classical novae are recurrent, on timescales of months6 to millennia7. 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 dwarfs8. Another type of outburst is the dwarf nova: these occur in binaries that have stellar masses and periods indistinguishable from those of novalikes9 but much lower mass-transfer rates10, when accretion-disk instabilities11 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 puzzle9. 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 novae14,15,16 display nova shells, but lack firm post-eruption ages17,18, and are also dwarf novae at present. We conclude that many old novae become dwarf novae for part of the millennia between successive nova eruptions19,20.
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J.M., K.I., K.D. and M.M.S. acknowledge support by the Polish Narodowe Centrum Nauki (grant DEC-2013/10/M/ST9/00086). M.M.S. acknowledges the late P. Newman and the Newman’s Own Foundation, whose support made the participation of the American Museum of Natural History (AMNH) in the South African Large Telescope (SALT) possible. A.F.J.M. thanks the National Sciences and Engineering Research Council of Canada and the Fonds de Recherche Nature et Technologies (Quebec) for financial support. A.P. acknowledges support from the AMNH’s Kathryn W. Davis Postdoctoral Scholar program, which is supported in part by the New York State Education Department and by the National Science Foundation (NSF) under grant numbers DRL-1119444 and DUE-1340006. M.M.S. acknowledges the hospitality of the Institute of Astronomy at the University of Cambridge. Some of the observations reported here were obtained with the SALT under programme 2016-1-SCI-044, and with the South African Astronomical Observatory’s 1.9-metre and 1.0-metre telescopes. Polish participation in SALT is funded by grant no. MNiSW DIR/WK/2016/07. We thank the Harvard–Smithsonian Center for Astrophysics team for making DASCH data available to the astronomical community. The DASCH project at Harvard is partially supported from NSF grants AST-0407380, AST-0909073 and AST-1313370. The Image Reduction and Analysis Facility (IRAF) is distributed by the National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy under a cooperative agreement with the NSF. This research has made use of data obtained from the Chandra Data Archive and software provided by the Chandra X-ray Center in application packages CIAO, ChIPS and Sherpa. All authors thank the referees for thoughtful and constructive suggestions.
The authors declare no competing financial interests.
Reviewer Information Nature thanks C. Knigge and S. Shore for their contribution to the peer review of this work.
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Extended data figures and tables
a–c, Phase plots of Nova 1437 photometry in V, g′ and B bands. The observations are phased with the orbital period (Porb), using the ephemeris of equation (1). d, Phase plot of g′ photometry, after subtracting all variability related to the orbital motion (see Methods). The observations were phased with the spin period (Pspin) of the white dwarf, using the ephemeris of equation (2). e, As for panel d, but with points binned with a bin size of 0.025 × Pspin. f, Chandra observations in the 0.2–10 keV band, phased with the spin period of the white dwarf using the ephemeris from equation (2). All error bars are 1σ.
Extended Data Figure 2 The phase dispersion minimization (PDM) statistic as a function of frequency for the light curves of Nova Scorpii 1437.
This PDM plot (see text) allows us to determine the binary orbital frequency to be 1.8725691 per day, corresponding to an orbital period of 0.5340257 days.
Measurements are shown in V, g′ and B filters, and the error bars are 1σ.
Extended Data Figure 4 SALT-based spectra of the nova shell, the old nova and a synthetic spectral standard.
Top, SALT spectra for the brightest region on the nova shell (southeast of the cataclysmic variable), with the main emission lines identified. Note the strong lines of [S II] 6,716 Å and 6,731 Å, and of [N II] at 6,548 Å and 6,583 Å. The y-axis shows the flux of the relevant emission line with respect to the flux of the Hα line. Bottom, SALT spectrum of the cataclysmic variable taken on 23 September 2016, with the synthetic spectrum of a K3 V star overlaid (with effective temperature Teff = 4,750 K, gravitational acceleration log g = 4.5, and Solar composition), reddened with A(V) ≈ 1. The insert shows the emission profiles of Hβ as well as those of He II and the Bowen C III-N III blend.
The radial velocities (VHEL, where ‘HEL’ is ‘heliocentric’) were obtained by measuring the wavelength differences between the 20 strongest absorption features in the observed spectrum and those in the synthetic spectrum of Fig. 4. The systemic velocity is −46 km per second, and the error bars are 1σ. The solid curve corresponds to the secondary star’s inferior conjunction occurring at mid-eclipse. The (better-fitting) dashed curve corresponds to the inferior conjunction that occurs 0.035 orbital periods after the eclipse. See text for details. Tconj and Tecl, time of conjunction and time of eclipse.
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Shara, M., Iłkiewicz, K., Mikołajewska, J. et al. Proper-motion age dating of the progeny of Nova Scorpii AD 1437. Nature 548, 558–560 (2017) doi:10.1038/nature23644
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