The double-degenerate, super-Chandrasekhar nucleus of the planetary nebula Henize 2-428

Journal name:
Nature
Volume:
519,
Pages:
63–65
Date published:
DOI:
doi:10.1038/nature14124
Received
Accepted
Published online

The planetary nebula stage is the ultimate fate of stars with masses one to eight times that of the Sun ( ). The origin of their complex morphologies is poorly understood1, although several mechanisms involving binary interaction have been proposed2, 3. In close binary systems, the orbital separation is short enough for the primary star to overfill its Roche lobe as the star expands during the asymptotic giant branch phase. The excess gas eventually forms a common envelope surrounding both stars. Drag forces then result in the envelope being ejected into a bipolar planetary nebula whose equator is coincident with the orbital plane of the system. Systems in which both stars have ejected their envelopes and are evolving towards the white dwarf stage are said to be double degenerate. Here we report that Henize 2-428 has a double-degenerate core with a combined mass of ~1.76 , which is above the Chandrasekhar limit (the maximum mass of a stable white dwarf) of 1.4 . This, together with its short orbital period (4.2 hours), suggests that the system should merge in 700 million years, triggering a type Ia supernova event. This supports the hypothesis of the double-degenerate, super-Chandrasekhar evolutionary pathway for the formation of type Ia supernovae4.

At a glance

Figures

  1. Close-up view of the bipolar planetary nebula Henize 2-428.
    Figure 1: Close-up view of the bipolar planetary nebula Henize 2-428.

    This 2-h exposure in Hα 656.3 nm was observed with the INT/WFC. North is up and East is to the left.

  2. Light-curve measurements and model.
    Figure 2: Light-curve measurements and model.

    a, Light curves of Henize 2-428 in the Johnson B-band and Sloan i-band filters (0.44 µm and 0.78 µm, respectively) and model, along with their respective residuals (b). The B-band data have been shifted up by one magnitude for display purposes. The data are shown here folded on the orbital period of the system—0.1758 day (or 4.2 h)—along with the model (solid line). Error bars represent 1σ formal measurement errors.

  3. Time evolution of the spectrum profile of Henize 2-428.
    Figure 3: Time evolution of the spectrum profile of Henize 2-428.

    The double He ii 541.2 nm absorption lines show clear Doppler shifts in the VLT spectra. The flux is normalized with respect to the continuum. Velocities with respect to the He ii 541.2 nm rest wavelength are displayed on the x axis. The top spectrum (a) corresponds to the night of 19 June 2010, while the three remaining, consecutive spectra were taken on 8 July 2012 and are chronologically ordered from top to bottom (bd).

  4. Radial-velocity measurements and orbit solution.
    Figure 4: Radial-velocity measurements and orbit solution.

    a, Radial-velocity curves of the central stars of Henize 2-428 obtained with GTC/OSIRIS on 11 August 2013, and the model, along with their respective residuals (b). The data have been folded on the 4.2-h period determined in the text. The primary star is depicted by black points and the secondary star by white ones, and the dashed horizontal line represents the systemic velocity. Error bars represent 1σ formal measurement errors.

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Author information

Affiliations

  1. Observatorio Astronómico Nacional, Apartado de Correos 112, E-28803, Alcalá de Henares, Spain

    • M. Santander-García
  2. Instituto de Ciencia de Materiales de Madrid (CSIC), Sor Juana Inés de la Cruz, 3, E-28049 Madrid, Spain

    • M. Santander-García
  3. Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain

    • P. Rodríguez-Gil,
    • R. L. M. Corradi &
    • D. Jones
  4. Departamento de Astrofísica, Universidad de La Laguna, E-38205 La Laguna, Tenerife, Spain

    • P. Rodríguez-Gil,
    • R. L. M. Corradi &
    • D. Jones
  5. South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa

    • B. Miszalski &
    • M. M. Kotze
  6. Southern African Large Telescope Foundation, PO Box 9, Observatory 7935, South Africa

    • B. Miszalski
  7. European Southern Observatory, Alonso de Córdova 3107, 19001 Casilla, Santiago, Chile

    • H. M. J. Boffin
  8. Centro de Astrobiología, CSIC-INTA, Carretera de Torrejón a Ajalvir, km 4, E-28850 Torrejón de Ardoz, Spain

    • M. M. Rubio-Díez

Contributions

M.S.-G., P.R.-G., D.J., M.M.R.-D., H.M.J.B. and M.M.K. conducted the observations at the various telescopes. M.S.-G., P.R.-G., D.J. and M.M.K. reduced the data. M.S.-G. performed the light-curve and radial-velocity-curve modelling, and wrote the paper. All authors discussed the results and implications and commented on the manuscript at all stages.

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The authors declare no competing financial interests.

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