Decades ago, γ-ray observatories identified diffuse Galactic emission at 1.809 MeV1,2,3 originating from β+ decays of an isotope of aluminium, 26Al, that has a mean lifetime of 1.04 million years4. Objects responsible for the production of this radioactive isotope have never been directly identified owing to insufficient angular resolutions and sensitivities of the γ-ray observatories. Here, we report observations of millimetre-wave rotational lines of the isotopologue of aluminium monofluoride that contains the radioactive isotope (26AlF). The emission is observed towards CK Vul, which is thought to be a remnant of a stellar merger5,6,7. Our constraints on the production of 26Al, combined with the estimates on the merger rate, make it unlikely that objects similar to CK Vul are major producers of Galactic 26Al. However, the observation may be a stepping stone for unambiguous identification of other Galactic sources of 26Al. Moreover, a high content of 26Al in the remnant indicates that, before the merger, the CK Vul system contained at least one solar-mass star that evolved to the red giant branch.

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  1. 1.

    Mahoney, W. A., Ling, J. C., Jacobson, A. S. & Lingenfelter, R. E. Diffuse galactic gamma-ray line emission from nucleosynthetic Fe-60, Al-26, and Na-22—preliminary limits from HEAO 3. Astrophys. J. 262, 742 (1982).

  2. 2.

    Mahoney, W. A., Ling, J. C., Wheaton, W. A. & Jacobson, A. S. HEAO 3 discovery of Al-26 in the interstellar medium. Astrophys. J. 286, 578 (1984).

  3. 3.

    Diehl, R. et al. COMPTEL observations of Galactic 26Al emission. Astron. Astrophys. 298, 445 (1995).

  4. 4.

    Samworth, E. A., Warburton, E. K. & Engelbertink, G. A. P. Beta decay of the 26Al ground state. Phys. Rev. C 5, 138–142 (1972).

  5. 5.

    Kamiński, T. et al. Nuclear ashes and outflow in the eruptive star Nova Vul 1670. Nature 520, 322–324 (2015).

  6. 6.

    Kato, T. CK Vul as a candidate eruptive stellar merging event. Astron. Astrophys. 399, 695–697 (2003).

  7. 7.

    Tylenda, R. et al. OGLE-2002-BLG-360: from a gravitational microlensing candidate to an overlooked red transient. Astron. Astrophys. 555, A16 (2013).

  8. 8.

    Hevelius, J. An extract of a letter, written to the publisher by the excellent Johannes Hevelius, concerning his further observations of the new star near the beak of the Swan. Phil. Trans. R. Soc. Lond. I 6, 2197 (1671).

  9. 9.

    Shara, M. M., Moffat, A. F. J. & Webbink, R. F. Unraveling the oldest and faintest recovered nova—CK Vulpeculae (1670). Astrophys. J. 294, 271–285 (1985).

  10. 10.

    Tylenda, R. & Soker, N. Eruptions of the V838 Mon type: stellar merger versus nuclear outburst models. Astron. Astrophys. 451, 223–236 (2006).

  11. 11.

    Tylenda, R. et al. V1309 Scorpii: merger of a contact binary. Astron. Astrophys. 528, AA114 (2011).

  12. 12.

    Kamiński, T. et al. Organic molecules, ions, and rare isotopologues in the remnant of the stellar-merger candidate, CK Vulpeculae (Nova 1670). Astron. Astrophys. 607, A78 (2017).

  13. 13.

    Oberlack, U. et al. COMPTEL limits on 26Al 1.809 MeV line emission from γ2 Velorum. Astron. Astrophys. 353, 715–721 (2000).

  14. 14.

    Guelin, M. et al. Nucleosynthesis in AGB stars: observation of 25Mg and 26Mg in IRC + 10216 and possible detection of 26Al. Astron. Astrophys. 297, 183–196 (1995).

  15. 15.

    Banerjee, D. P. K. et al. A search for radioactive 26Al in the nova-like variable V4332 Sagittarii. Astrophys. J. 610, L29–L32 (2004).

  16. 16.

    Hajduk, M. et al. The enigma of the oldest ‘nova’: the central star and nebula of CK Vul. Mon. Not. R. Astron. Soc. 378, 1298–1308 (2007).

  17. 17.

    Hajduk, M., van Hoof, P. A. M. & Zijlstra, A. A. CK Vul: evolving nebula and three curious background stars. Mon. Not. R. Astron. Soc. 432, 167–175 (2013).

  18. 18.

    Highberger, J. L., Savage, C., Bieging, J. H. & Ziurys, L. M. Heavy‐metal chemistry in proto-planetary nebulae: detection of MgNC, NaCN, and AlF toward CRL 2688. Astrophys. J. 562, 790–798 (2001).

  19. 19.

    Agúndez, M. et al. Molecular abundances in the inner layers of IRC 10216. Astron. Astrophys. 543, A48 (2012).

  20. 20.

    Andreazza, C. M. & Almeida, A. A. D. The formation of AlF by radiative association. Mon. Not. R. Astron. Soc. 437, 2932–2935 (2013).

  21. 21.

    Arnould, M., Goriely, S. & Jorissen, A. Non-explosive hydrogen and helium burnings: abundance predictions from the NACRE reaction rate compilation. Astron. Astrophys. 347, 572–582 (1999).

  22. 22.

    Karakas, A. & Lattanzio, J. C. Stellar models and yields of asymptotic giant branch stars. Publ. Astron. Soc. Aust. 24, 103–117 (2007).

  23. 23.

    Evans, A. et al. CK Vul: a smorgasbord of hydrocarbons rules out a 1670 nova (and much else besides). Mon. Not. R. Astron. Soc. 457, 2871–2876 (2016).

  24. 24.

    Karakas, A. I. & Lugaro, M. Stellar yields from metal-rich asymptotic giant branch models. Astrophys. J. 825, 26 (2016).

  25. 25.

    Politano, M., Sluys, M. V. D., Taam, R. E. & Willems, B. Population synthesis of common envelope mergers. I. Giant stars with stellar or substellar companions. Astrophys. J. 720, 1752–1766 (2010).

  26. 26.

    Kochanek, C. S., Adams, S. M. & Belczynski, K. Stellar mergers are common. Mon. Not. R. Astron. Soc. 443, 1319–1328 (2014).

  27. 27.

    Glassgold, A. E. 26Al and circumstellar envelopes. Astrophys. J. 438, L111–L114 (1995).

  28. 28.

    Indriolo, N. et al. Herschel survey of galactic OH+, H2O+, and H3O+: probing the molecular hydrogen fraction and cosmic-ray ionization rate. Astrophys. J. 800, 40 (2015).

  29. 29.

    Diehl, R. et al. Radioactive 26Al from massive stars in the Galaxy. Nature 439, 45–47 (2006).

  30. 30.

    Diehl, R. et al. INTEGRAL/SPI gamma-ray line spectroscopy. Preprint at https://arxiv.org/abs/1710.10139 (2017).

  31. 31.

    Hedderich, H. G. & Bernath, P. F. The infrared emission spectrum of gaseous AlF. J. Mol. Spectrosc. 153, 73–80 (1992).

  32. 32.

    Hoeft, J., Lovas, F. & Tiemann, E. et al. Microwave absorption spectra of AlF, GaF, InF, and TIF. Z. Naturforsch. A 25, 1029–1035 (2014).

  33. 33.

    Lide, D. R. High‐temperature microwave spectroscopy. AlF and AlCl. J. Chem. Phys. 42, 1013–1018 (1965).

  34. 34.

    Western, C. M. PGOPHER: a program for simulating rotational, vibrational and electronic spectra. J. Quant. Spectrosc. Radiat. Transf. 186, 221–242 (2017).

  35. 35.

    Dunham, J. L. The energy levels of a rotating vibrator. Phys. Rev. 41, 721–731 (1932).

  36. 36.

    Lutz, J. J. & Hutson, J. M. Deviations from Born–Oppenheimer mass scaling in spectroscopy and ultracold molecular physics. J. Mol. Spectrosc. 330, 43–56 (2016).

  37. 37.

    McMullin, J. P., Waters, B., Schiebel, D., Young, W. & Golap, K. CASA architecture and applications. In Astronomical Data Analysis Software and Systems XVI (eds Shaw, R. A., Hill, F. & Bell, D. J.) 376 (Conference Series Volume 127, Astronomical Society of the Pacific, 2007).

  38. 38.

    Goodman, J. & Weare, J. Ensemble samplers with affine invariance. Commun. Appl. Math. Comput. Sci. 5, 65–80 (2010).

  39. 39.

    Foreman-Mackey, D. et al. emcee: the MCMC hammer. Publ. Astron. Soc. Pac 125, 306 (2013).

  40. 40.

    Goldsmith, P. F. & Langer, W. D. Population diagram analysis of molecular line emission. Astrophys. J. 517, 209–225 (1999).

  41. 41.

    Gotoum, N., Hammami, K., Owono Owono, L. C. & Jaidane, N.-E. Collision induced rotational excitation of AlF (X1Σ+) by para-H2 (j = 0). Astrophys. Space Sci. 337, 553–561 (2011).

  42. 42.

    Gotoum, N. et al. Rotational excitation of aluminium monofluoride (AlF) by He atom at low temperature. Astrophys. Space Sci. 332, 209–217 (2010).

  43. 43.

    Lattanzio, J. C. The asymptotic giant branch evolution of 1.0–3.0 solar mass stars as a function of mass and composition. Astrophys. J. 311, 708 (1986).

  44. 44.

    Karakas, A. I. Helium enrichment and carbon-star production in metal-rich populations. Mon. Not. R. Astron. Soc. 445, 347–358 (2014).

  45. 45.

    Young, P. A. et al. Observational tests and predictive stellar evolution. Astrophys. J. 556, 230 (2001).

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We are grateful to the directors K. Schuster, P. Cox, S. Dougherty, T. van Zeeuw, R. Blundell and T. Beasley for granting us discretionary time at NOEMA, ALMA, APEX, SMA and JVLA. T.K. thanks L. Matrá for an introduction to Markov chain Monte Carlo methods. R.T. acknowledges support from grant 2017/27/B/ST9/01128, financed by the Polish National Science Centre. A.A.B. and T.F.G. acknowledge funding through the DFG priority programme 1573 (Physics of the Interstellar Medium) under grants GI 319/3-1 and GI 319/3-2, and the University of Kassel through P/1052 Programmlinie ‘Zukunft’. K.T.W. acknowledges support from the International Max Planck Research School for Astronomy and Astrophysics at the Universities of Bonn and Cologne, and also from the Bonn–Cologne Graduate School of Physics and Astronomy. This study made use of APEX, which is a collaboration between the Max-Planck-Institut für Radioastronomie, European Southern Observatory and Onsala Space Observatory. Some of the APEX data were collected under the programmes 095.F-9543(A) and 296.D-5009(A). This paper makes use of the following ALMA data: ADS/JAO.ALMA#2015.A.00013.S and #2017.A.00030.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities. The IRAM 30 m observations were carried out under projects 183-14, 161-15 and D07-14, and those with NOEMA under W15BN, E15AE, S16AV and E16AC. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). The IRAM observations were supported by funding from the European Commission Seventh Framework Programme (FP/2007-2013) under grant agreement number 283393 (RadioNet3).

Author information


  1. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA

    • Tomasz Kamiński
    •  & Nimesh A. Patel
  2. Department for Astrophysics, Nicolaus Copernicus Astronomical Center, Toruń, Poland

    • Romuald Tylenda
  3. Max-Planck-Institut für Radioastronomie, Bonn, Germany

    • Karl M. Menten
  4. Monash Centre for Astrophysics, School of Physics and Astronomy, Monash University, Clayton, Victoria, Australia

    • Amanda Karakas
  5. IRAM, Domaine Universitaire de Grenoble, Grenoble, France

    • Jan Martin Winters
    •  & Ka Tat Wong
  6. Laborastrophysik, Institut für Physik, Universität Kassel, Kassel, Germany

    • Alexander A. Breier
    •  & Thomas F. Giesen


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T.K. wrote the text and analysed the observations. A.A.B. and T.F.G. prepared the spectroscopic data. J.M.W. prepared, executed and calibrated the NOEMA observations. K.T.W. prepared and reduced the JVLA observations. T.K. prepared and reduced the ALMA and all single-dish observations. N.A.P. prepared and calibrated the SMA observations. R.T. and A.K. ran stellar-evolution models. All authors contributed to the interpretation of the data.

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The authors declare no competing interests.

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Correspondence to Tomasz Kamiński.

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