An eclipsing substellar binary in a young triple system discovered by SPECULOOS

Abstract

Mass, radius and age are three of the most fundamental parameters for celestial objects, enabling insight into the evolution and internal physics of stars, brown dwarfs and planets. Brown dwarfs are hydrogen-rich objects that are unable to sustain core fusion reactions but are supported against collapse by electron degeneracy pressure1. As they age, brown dwarfs cool, reducing their radius and luminosity. Young exoplanets follow a similar behaviour. Brown dwarf evolutionary models are relied upon to infer the masses, radii and ages of young brown dwarfs2,3. Similar models are also used to infer the mass and radius of directly imaged exoplanets4. Unfortunately, only sparse empirical mass, radius and age measurements are currently available, and so the models remain mostly unvalidated. Double-line eclipsing binaries provide the most direct route towards the absolute determination of the masses and radii of stars5,6,7. Here we report the discovery by SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) of the 2M1510A triple system, consisting of a nearby, eclipsing, double-line brown dwarf binary and a widely separated tertiary brown dwarf companion. We find that the system is a member of Argus, a 45 ± 5 million-year-old moving group8,9. The system’s age matches those of currently known directly imaged exoplanets so 2M1510A provides an opportunity to benchmark evolutionary models of brown dwarfs and young planets. We find that widely used evolutionary models3 do reproduce the mass, radius and age of the binary components remarkably well, but overestimate their luminosity by up to 0.65 magnitudes, which could result in underestimations of 20% to 35% of photometric masses for directly imaged exoplanets and young-field brown dwarfs.

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Fig. 1: Data demonstrating that 2M1510A is a substellar eclipsing binary.
Fig. 2: Mass–radius diagram showing the position of the 2M1510Aab eclipsing pair (shown in black with their 1σ uncertainties).
Fig. 3: Radius and luminosity measurements as a function of system age, for stars, brown dwarfs and giant exoplanets with their 1σ uncertainties.

Data availability

All reduced photometric timeseries will be made available for download at the CDS, and on request to A.H.M.J.T. Raw SPECULOOS CCD frames will become available through the ESO archive in January 2021; they can be requested from the authors before this date. Eventually the archive will also contain lightcurves for all reference stars in the frames as well. Our UVES spectra are now publicly available on the ESO archive, and can be found by searching the archive for ProgID 299.C-5046 and 2100.C-5024. MONET-South raw images can be made available upon request. NIRSPEC spectra are available at the Keck Observatory Archive, and can be found be searching the archive for Principal Investigator A.J.B. and programmes U009, U010 and U136. SpeX spectra are now available via SPLAT (https://github.com/aburgasser/splat). Requests concerning the data used in this publication can be addressed to A.H.M.J.T. and A.J.B. Figure 1 contains SPECULOOS photometry, as well as UVES and NIRSPEC spectra.

Code availability

The photometric reduction packages use standard public routines such as PyRAF and astropy. Radial velocities were extracted from UVES and NIRSpec data from a code built from elements of SPLAT (https://github.com/aburgasser/splat). The amelie code combines ellc and emcee (see text), which are both public codes. amelie can be made available upon request, and a stable version is planned to be released on GitHub.

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Acknowledgements

We thank the personnel of ESO who host SPECULOOS at Paranal Observatory, and who have awarded two Director Discretionary Time (DDT) programmes to confirm this object (Prog ID 099.C-0138 and 2100.C-5024, Principal Investigator A.H.M.J.T.). In addition, we thank C. Alvarez, G. Doppman, P. Gomez, H. Hershey and J. Rivera at the Keck Observatory and G. Osterman and E. Volquardsen at the Infra-Red Telescope Facility, for their assistance with the observations reported here. This work also used observations from the Las Cumbres Observatory Global Telescope network, awarded through a DDT programme (PI Alonso). We made use of PyRAF, which is a product of the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA) for NASA. PyRAF uses the Image Reduction and Analysis Facility, which is distributed by the National Optical Astronomy Observatory, which is operated by AURA, under cooperative agreement with the National Science Foundation. We used the SIMBAD database, operated at Centre de Données astronomique de Strasbourg, Strasbourg, France; NASA’s Astrophysics Data System Bibliographic Services; the M, L, T and Y dwarf compendium housed at DwarfArchives.org; and the SpeX Prism Libraries (http://www.browndwarfs.org/spexprism). We recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate and grateful to have the opportunity to conduct observations from this mountain. This research also made use of Astropy (www.astropy.org), a community-developed core python package for astronomy as well as the open-source python packages numpy (www.numpy.org), scipy (www.scipy.org) and matplotlib (www.matplotlib.org). A.H.M.J.T. received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement number 803193/BEBOP). A.H.M.J.T. also received funding from the Leverhulme Trust (Research Project Grant number RPG-2018-418) and from the Science, Technology and Facilities Council (grant number ST/S00193X/1). A.J.B. acknowledges funding support from the National Science Foundation (award number AST-1517177). The material is based upon work supported by NASA (grant number NNX15AI75G). B.-O.D. acknowledges support from the Swiss National Science Foundation (PP00P2-163967). M.G. received funding from the ERC (FP/2007-2013 grant agreement number 336480/SPECULOOS), from an ARC grant for Concerted Research Actions, financed by the Wallonia-Brussels Federation, from the Simons Foundation, and from the MERAC foundation. M.G. and E.J. are Senior Research Associates at the Fonds de la Recherche Scientifique–Fond National de la Recherche Scientifique. L.D. acknowledges support from the Gruber Foundation Fellowship. V.K.H. is supported by a generous Birmingham Doctoral Scholarship and by a studentship from Birmingham’s School of Physics and Astronomy.

Author information

A.H.M.J.T. led the data acquisition, obtained UVES data, and organised the analysis and interpretation of this system. A.J.B. obtained the NIRSPEC data, extracted radial velocities from NIRSPEC and UVES data, produced early parameters of the system, and performed the spectral typing and assessment of Argus membership. A.B. and V.K.H. led the photometric follow-up. A.B., E.D., C.M., P.P.P., L.D. and M.G. reduced the photometric data. V.K.H. produced the global analysis. M.G., E.J., D.S., B.-O.D., D.Q., L.D., C.M., P.P.P., J.d.W., A.H.M.J.T., E.D., A.B. and S.T. participated with the preparation, construction and running of the SPECULOOS facility/survey. J.MC. provided the DONUTS software used for guiding. D.B.G. provided the SpeX data while R.A., F.H. and T.-O.H. participated in the photometric follow-up. V.V.G. calculated stellar models. All authors assisted in writing the manuscript.

Correspondence to Amaury H. M. J. Triaud or Adam J. Burgasser.

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Peer review information Nature Astronomy thanks Víctor Béjar, Keivan Stassun and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Triaud, A.H.M.J., Burgasser, A.J., Burdanov, A. et al. An eclipsing substellar binary in a young triple system discovered by SPECULOOS. Nat Astron (2020). https://doi.org/10.1038/s41550-020-1018-2

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