Low-mass white-dwarf stars are the remnants of disrupted red-giant stars in binary millisecond pulsars1 and other exotic binary star systems2,3,4. Some low-mass white dwarfs cool rapidly, whereas others stay bright for millions of years because of stable fusion in thick surface hydrogen layers5. This dichotomy is not well understood, so the potential use of low-mass white dwarfs as independent clocks with which to test the spin-down ages of pulsars6,7 or as probes of the extreme environments in which low-mass white dwarfs form8,9,10 cannot fully be exploited. Here we report precise mass and radius measurements for the precursor to a low-mass white dwarf. We find that only models in which this disrupted red-giant star has a thick hydrogen envelope can match the strong constraints provided by our data. Very cool low-mass white dwarfs must therefore have lost their thick hydrogen envelopes by irradiation from pulsar companions11,12 or by episodes of unstable hydrogen fusion (shell flashes). We also find that this low-mass white-dwarf precursor is a type of pulsating star not hitherto seen. The observed pulsation frequencies are sensitive to internal processes that determine whether this star will undergo shell flashes.
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Lorimer, D. R. Binary and millisecond pulsars. Liv. Rev. Rel. 11, 8 (2008)
Kilic, M. et al. The ELM Survey. II. Twelve binary white dwarf merger systems. Astrophys. J. 727, 3 (2011)
Breton, R. P., Rappaport, S. A., van Kerkwijk, M. H. & Carter, J. A. KOI 1224: a fourth bloated hot white dwarf companion found with Kepler. Astrophys. J. 748, 115 (2012)
Hermes, J. J., Kilic, M., Brown, W. R., Montgomery, M. H. & Winget, D. E. Two new tidally distorted white dwarfs. Astrophys. J. 749, 42 (2012)
Webbink, R. F. Evolution of helium white dwarfs in close binaries. Mon. Not. R. Astron. Soc. 171, 555–568 (1975)
Kiziltan, B. & Thorsett, S. E. Millisecond pulsar ages: implications of binary evolution and a maximum spin limit. Astrophys. J. 715, 335–341 (2010)
van Kerkwijk, M. H., Bassa, C. G., Jacoby, B. A. & Jonker, P. G. Optical studies of companions to millisecond pulsars. Astron. Soc. Pacif. Conf. Ser. 328, 357–370 (2005)
Gezari, S. et al. An ultraviolet-optical flare from the tidal disruption of a helium-rich stellar core. Nature 485, 217–220 (2012)
Knigge, C. et al. Stellar exotica in 47 Tucanae. Astrophys. J. 683, 1006–1030 (2008)
Strickler, R. R. et al. Helium-core white dwarfs in the globular cluster NGC 6397. Astrophys. J. 699, 40–55 (2009)
Ergma, E., Sarna, M. J. & Gerškevitš-Antipova, J. The helium white dwarf in two pulsars: too cool in PSR J0751+1807 and too hot in PSR J1012+5307? Mon. Not. R. Astron. Soc. 321, 71–76 (2001)
Breton, R. P. et al. Discovery of the optical counterparts to four energetic Fermi millisecond pulsars. Astrophys. J. 769, 108 (2013)
Althaus, L. G., Serenelli, A. M. & Benvenuto, O. G. Diffusion and the occurrence of hydrogen-shell flashes in helium white dwarf stars. Mon. Not. R. Astron. Soc. 323, 471–483 (2001)
Driebe, T., Schönberner, D., Blöcker, T. & Herwig, F. The evolution of helium white dwarfs. I. The companion of the millisecond pulsar PSR J1012+5307. Astron. Astrophys. 339, 123–133 (1998)
Iben, I., Jr & Tutukov, A. V. On the formation and evolution of a helium degenerate dwarf in a close binary. Astrophys. J. 311, 742–752 (1986)
Bassa, C. G., van Kerkwijk, M. H. & Kulkarni, S. R. The ultra-cool white dwarf companion of PSR J0751+1807. Astron. Astrophys. 450, 295–303 (2006)
Espinoza, C. M., Lyne, A. G., Kramer, M., Manchester, R. N. & Kaspi, V. M. The braking index of PSR J1734–3333 and the magnetar population. Astrophys. J. 741, L13 (2011)
Noutsos, A., Schnitzeler, D., Keane, E., Kramer, M. & Johnston, S. Pulsar spin-velocity alignment: kinematic ages, birth periods and braking indices. Mon. Not. R. Astron. Soc. 430, 2281–2301 (2013)
Maxted, P. F. L. et al. Discovery of a stripped red giant core in a bright eclipsing binary system. Mon. Not. R. Astron. Soc. 418, 1156–1164 (2011)
Nelson, L. A., Dubeau, E. & MacCannell, K. A. Evolutionary properties of helium-rich, degenerate dwarfs in binaries containing compact companions. Astrophys. J. 616, 1124–1147 (2004)
Bíró, I. B. & Nuspl, J. Photometric mode identification methods of non-radial pulsations in eclipsing binaries—I. Dynamic eclipse mapping. Mon. Not. R. Astron. Soc. 416, 1601–1615 (2011)
Aerts, C., Christensen-Dalsgaard, J. & Kurtz, D. W. Asteroseismology Ch. 6 (Springer, 2010)
Beck, P. G. et al. Fast core rotation in red-giant stars as revealed by gravity-dominated mixed modes. Nature 481, 55–57 (2012)
Dupret, M.-A. et al. Asteroseismology of the β Cep star HD 129929. II. Seismic constraints on core overshooting, internal rotation and stellar parameters. Astron. Astrophys. 415, 251–257 (2004)
Maxted, P. F. L. et al. Discovery of a stripped red-giant core in a bright eclipsing binary star. In Fifth Meeting on Hot Subdwarf Stars and Related Objects ASP Conf. Ser. Vol. 452, 137–146 (Astronomical Society of the Pacific, 2012)
Dhillon, V. et al. ULTRACAM: an ultrafast, triple-beam CCD camera for high-speed astrophysics. Mon. Not. R. Astron. Soc. 378, 825–840 (2007)
Dotter, A. et al. The Dartmouth Stellar Evolution Database. Astrophys. J. 178 (Supp.). 89–101 (2008)
Dupret, M.-A., Grigahcène, A., Garrido, R., Gabriel, M. & Scuflaire, R. Theoretical instability strips for δ Scuti and γ Doradus stars. Astron. Astrophys. 414, L17–L20 (2004)
We thank the ESO staff who obtained our UVES data for carefully scheduling the observations at the correct orbital phases. We thank A. Cherman and D. Kurtz for comments on a draft version of the paper. This work is based on observations collected at the ESO, Chile (program ID: 086.D-0194). A.M.S. is partially supported by a Re-integration Grant (PIRG-GA-2009-247732; FP7-People), and a MICINN grant (AYA2011-24704). V.S. acknowledges funding by the Deutsches Zentrum für Luft- und Raumfahrt (grant 50 OR 1110) and by the Erika-Giehrl-Stiftung. T.R.M. acknowledges funding from the UK Science and Technology Facilities Council (ST/I001719/1).
The authors declare no competing financial interests.
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Maxted, P., Serenelli, A., Miglio, A. et al. Multi-periodic pulsations of a stripped red-giant star in an eclipsing binary system. Nature 498, 463–465 (2013). https://doi.org/10.1038/nature12192
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