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An irradiated-Jupiter analogue hotter than the Sun

Nature Astronomy volume 7, pages 1329–1340 (2023)Cite this article

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Abstract

Planets orbiting close to hot stars experience intense extreme-ultraviolet radiation, potentially leading to atmosphere evaporation and to thermal dissociation of molecules. However, this extreme regime remains mainly unexplored due to observational challenges. Only a single known ultra-hot giant planet, KELT-9b, receives enough ultraviolet radiation for molecular dissociation, with a day-side temperature of ~4,600 K. An alternative approach uses irradiated brown dwarfs as hot-Jupiter analogues. With atmospheres and radii similar to those of giant planets, brown dwarfs orbiting close to hot Earth-sized white dwarf stars can be directly detected above the glare of the star. Here we report observations revealing an extremely irradiated low-mass companion to the hot white dwarf WD 0032–317. Our analysis indicates a day-side temperature of ~8,000 K, and a day-to-night temperature difference of ~6,000 K. The amount of extreme-ultraviolet radiation (with wavelengths 100–912 Å) received by WD 0032–317B is equivalent to that received by planets orbiting close to stars as hot as late B-type stars, and about 5,600 times higher than that of KELT-9b. With a mass of ~75–88 Jupiter masses, this near-hydrogen-burning-limit object is potentially one of the most massive brown dwarfs known.

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Fig. 1: Phased radial-velocity curves of WD 0032–317.
Fig. 2: Observed spectral energy distribution for WD 0032–317 compared to the best-fitting composite theoretical model spectra of a white dwarf and a black body or a brown dwarf.
Fig. 3: Equilibrium temperature of WD 0032–317 compared to other known systems.
Fig. 4: Brown-dwarf and low-mass stars mass–radius relation.

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Data availability

The UVES spectroscopic data are available through the ESO archive facility (http://archive.eso.org/cms.html) under programme IDs 165.H-0588(A), 0103.D-0731(A) and 105.20NQ.001. The FLAMINGOS-2 spectroscopic data are available through the Gemini Observatory archive (https://archive.gemini.edu) under programme ID GS-2022A-FT-108. The LCOGT photometric data are available at the LCOGT science archive (https://archive.lco.global) under programme IDs TAU2021B-004 and TAU2022B-004. The TESS photometric data are publicly available from the Mikulski Archive for Space Telescopes (MAST; https://mast.stsci.edu). The WISE photometric data are publicly available from the Infrared Processing and Analysis Center (IPAC) Infrared Science Archive (IRSA; https://irsa.ipac.caltech.edu/). The white dwarf theoretical evolutionary tracks used in the analysis will be published in a future publication led by A.G.I. and are available upon request from the corresponding author. Source data are provided with this paper.

Code availability

This research has made use of the Python package GAIAXPY (https://gaia-dpci.github.io/GaiaXPy-website/, https://doi.org/10.5281/zenodo.7374213), developed and maintained by members of the Gaia Data Processing and Analysis Consortium (DPAC), and in particular, Coordination Unit 5 (CU5) and the Data Processing Centre located at the Institute of Astronomy, Cambridge, UK (DPCI); and ASTROPY (http://www.astropy.org), a community-developed core Python package for Astronomy87,88, CORNER89, EMCEE61, LIGHTKURVE90, MATPLOTLIB91, NUMPY92,93, SCIPY94, SPARTA (https://github.com/SPARTA-dev/SPARTA), STSYNPHOT95, SYNPHOT96 and UNCERTAINTIES (http://pythonhosted.org/uncertainties/), a Python package for calculations with uncertainties by E. O. Lebigot.

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Acknowledgements

We thank S. Shahaf for useful discussions, J. Spyromilio for comments on the observing proposals and manuscript, J. Pritchard from ESO User Support for assistance with the observation planning and A. Binnenfeld for help in verifying the orbital period. This work was supported by a Benoziyo-prize postdoctoral fellowship (N.H.). This work was supported by a grant from the European Research Council (ERC) under the European Union’s FP7 Programme, Grant No. 833031 (D.M.). A.G.I. acknowledges support from the Netherlands Organisation for Scientific Research (NWO). C.B. acknowledges support from the National Science Foundation grant no. AST-1909022. E.B. acknowledges support from the Science and Technology Facilities Council (STFC) grant no. ST/S000623/1. B.T.G. acknowledges support from the UK’s Science and Technology Facilities Council (STFC), grant no. ST/T000406/1. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement no. 101020057). A.R.M. acknowledges support from the Spanish MINECO grant no. PID2020-117252GB-I00 and from the AGAUR/Generalitat de Catalunya grant no. SGR-386/2021. F.M. acknowledges support from the INAF Large Grant ‘Dual and binary supermassive black holes in the multi-messenger era: from galaxy mergers to gravitational waves’ (Bando Ricerca Fondamentale INAF 2022), from the INAF project ‘VLT-MOONS’ CRAM 1.05.03.07. Based on observations collected at the European Southern Observatory under ESO programmes 165.H-0588(A), 0103.D-0731(A) and 105.20NQ.001. This research has made use of the services of the ESO Science Archive Facility. This work makes use of observations from the Las Cumbres Observatory global telescope network under programme TAU2021B-004. This work is based on observations obtained at the international Gemini Observatory, a programme of NSF’s NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory Partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil) and Korea Astronomy and Space Science Institute (Republic of Korea). This work was enabled by observations made from the Gemini North telescope, located within the Maunakea Science Reserve and adjacent to the summit of Maunakea. We are grateful for the privilege of observing the Universe from a place that is unique in both its astronomical quality and its cultural significance. This paper includes data collected by the TESS mission, which are publicly available from the Mikulski Archive for Space Telescopes (MAST). Funding for the TESS mission is provided by the NASA’s Science Mission Directorate. This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France. This research has made use of the Spanish Virtual Observatory (http://svo.cab.inta-csic.es) supported from Ministerio de Ciencia e Innovación through grant no. PID2020-112949GB-I00. This publication makes use of data products from the Wide-Field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.

Author information

Author notes

  1. Deceased: Thomas R. Marsh.

Authors and Affiliations

  1. Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot, Israel

    Na’ama Hallakoun

  2. School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv, Israel

    Dan Maoz

  3. Department of Astrophysics/IMAPP, Radboud University Nijmegen, Nijmegen, the Netherlands

    Alina G. Istrate & Gijs Nelemans

  4. Department of Physics and Astronomy and Pittsburgh Particle Physics, Astrophysics and Cosmology Center (PITT PACC), University of Pittsburgh, Pittsburgh, PA, USA

    Carles Badenes

  5. Institute of Astronomy, University of Cambridge, Cambridge, UK

    Elmé Breedt

  6. Department of Physics, University of Warwick, Coventry, UK

    Boris T. Gänsicke & Thomas R. Marsh

  7. Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ, USA

    Saurabh W. Jha

  8. European Southern Observatory, Garching, Germany

    Bruno Leibundgut & Ferdinando Patat

  9. INAF – Osservatorio Astrofisico di Arcetri, Firenze, Italy

    Filippo Mannucci

  10. Institute for Astronomy, KU Leuven, Leuven, Belgium

    Gijs Nelemans

  11. SRON, Netherlands Institute for Space Research, Leiden, the Netherlands

    Gijs Nelemans

  12. Departament de Física, Universitat Politècnica de Catalunya, Castelldefels, Spain

    Alberto Rebassa-Mansergas

  13. Institut d’Estudis Espacials de Catalunya, Ed. Nexus-201, Barcelona, Spain

    Alberto Rebassa-Mansergas

Authors
  1. Na’ama Hallakoun
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  2. Dan Maoz
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  3. Alina G. Istrate
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  4. Carles Badenes
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  5. Elmé Breedt
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  6. Boris T. Gänsicke
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  7. Saurabh W. Jha
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  8. Bruno Leibundgut
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  9. Filippo Mannucci
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  10. Thomas R. Marsh
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  11. Gijs Nelemans
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  12. Ferdinando Patat
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  13. Alberto Rebassa-Mansergas
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Contributions

N.H. led the observational follow-up effort, analysed the data and wrote the majority of this manuscript. D.M. and N.H. analysed the original SPY survey data and flagged this object as a potential binary system. A.G.I. generated and fitted the helium- and hybrid-core white dwarf models. S.W.J. was the principal investigator of the Gemini follow-up programme. B.L., T.R.M. and G.N. were part of the team of the original SPY programme. All of the authors applied for spectroscopic follow-up telescope time, contributed to the discussion and commented on the manuscript.

Corresponding author

Correspondence to Na’ama Hallakoun.

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The authors declare no competing interests.

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Nature Astronomy thanks the anonymous reviewers for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Hα line profile of WD0032–317 as a function of orbital phase.

Hα line profile (black) and fit (red) of all the UVES epochs, vertically shifted for visual clarity, and sorted by orbital phase from bottom to top. The absorption line of the white-dwarf component is seen in all the epochs, while the inverted-core emission from the companion disappears when its night side is facing us.

Extended Data Fig. 2 Binned and normalised spectra of all the UVES epochs, vertically shifted for visual clarity, and sorted by orbital phase from bottom to top.

The Balmer line absorption of the white dwarf is seen throughout the orbital phase, while the companion’s Balmer line emission is visible between phases 0.19 and 0.81. Other spectral lines seen in the spectra are of either telluric or interstellar origin, with fixed radial velocities with respect to the system’s components.

Extended Data Fig. 3 Lomb-Scargle periodogram of the radial-velocity curve of the white-dwarf component.

The false-alarm probability (FAP) levels of 0.1, 1, and 50% are marked with the red dashed lines.

Extended Data Fig. 4 One- and two-dimensional projections of the posterior probability distributions of the MCMC fit parameters for the radial-velocity curves.

The vertical dashed lines mark the median value and its 1σ uncertainty.

Extended Data Fig. 5 Folded light curves of WD0032–317.

Normalised (grey dots) and binned (black error bars) light curves of the WD0032–317 system from LCOGT (left), WISE W1 band (top right; unbinned), and TESS (middle and bottom right), phase-folded over the orbital period (P = 8340.9090 s). No phase shift is seen between the various bands. The orbital period matches the one obtained from the spectroscopy. The error bars of the binned light curves show 1.48 times the median absolute deviation of the flux divided by the square root of the number of data points in each bin. A sine function fitted to orbital phases ∣φ∣> 0.2 is plotted in red. The residual plot for each model is shown in the sub-panel below each light curve. The illustrations on top demonstrate the system’s configuration at each orbital phase. The flat bottom corresponds to the companion’s night side.

Source data

Extended Data Fig. 6 Lomb-Scargle periodogram of the various light curves (see Extended Data Fig. 5).

The false-alarm probability (FAP) level of 0.01% (or 10% for the WISE W1 band) is marked with a red dashed line. The frequency of the highest peak in all of the light curves is consistent with the one of the radial-velocity curve (Extended Data Fig. 3).

Extended Data Fig. 7 Observed spectral energy distribution for WD0032–317 compared to the best-fitting composite theoretical model spectra of a white dwarf and a black body/brown dwarf.

The archival GALEX ultraviolet photometry, where the contribution from the companion is negligible, appears as blue square-shaped error bars. Minimal/maximal photometric values in different bands, extracted from the light curves, appear as green-shades circle-shaped error bars for LCOGT’s r′, i′, and z bands, and as red-shades diamond-shaped error bars for the WISE W1 band. A theoretical model spectrum of a hydrogen-dominated white dwarf with an effective temperature of 37,000K and a surface gravity log g=7.263 is shown in dashed light blue. The best-fitting brown-dwarf (64,65; for the night side, with [M/H] = -0.5 (He) or [M/H] = -1.0 (hybrid) and log g = 5.5) and black-body (for the day side) models are plotted in solid purple and dotted orange, respectively. The theoretical spectra were scaled using the system’s distance measured by the Gaia mission, and the estimated component radii (left: assuming a helium-core white dwarf (He), right: assuming a ‘hybrid’ carbon-oxygen core white dwarf with a thick helium envelope). The brown-dwarf model is shown multiplied by a factor of 4, to fit the displayed range. The composite model of the system at orbital phase 0 (0.5) is plotted in solid dark grey (black). The units shown on the y axis are the flux per wavelength, λ, multiplied by λ4, for visual clarity. The bottom panels show the residuals of the day-side (middle) and the night-side (bottom) fits. The error bars in the residual plots show the standard deviation and take into account both the photometric and the model uncertainties.

Extended Data Fig. 8 One- and two-dimensional projections of the posterior probability distributions of the MCMC fit parameters for the SED, assuming a He-core white dwarf.

The vertical dashed lines mark the median value and its 1σ uncertainty.

Extended Data Fig. 9 One- and two-dimensional projections of the posterior probability distributions of the MCMC fit parameters for the SED, assuming a hybrid-core white dwarf.

The vertical dashed lines mark the median value and its 1σ uncertainty.

Extended Data Fig. 10 Near-infrared spectra of WD0032–317.

Binned flux-calibrated Gemini South’s FLAMINGOS-2 near-infrared spectra of WD0032–317 (the unbinned spectra appear as semi-transparent lines), taken near orbital phases 0 (grey) and 0.35 (orange). The red ticks mark the hydrogen Brackett series in the reference frame of the companion. The Brackett 10 → 4 line is possibly seen in emission at ≈ 17,357 Å in the phase 0.35 spectrum. The greyed-out regions mark bands of high telluric atmospheric absorption. The bottom panel shows the phase-0 spectrum along with the theoretical models from Fig. 2, scaled to reflect their contribution at orbital phase 0: the white-dwarf model is plotted in dashed light blue, the brown-dwarf model is plotted in solid purple (multiplied by a factor of 20 for visual clarity), the black-body model is plotted in dotted orange, and the composite model is plotted in solid red.

Source data

Source data

Source Data Fig. 1

Radial velocity measurements.

Source Data Extended Data Fig. 5

Light curves from LCOGT (r′, i′, z bands) and WISE (W1 band).

Source Data Extended Data Fig. 10

Unbinned, flux-calibrated, Gemini South’s FLAMINGOS-2 spectra, taken near orbital phases 0 and 0.35.

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Hallakoun, N., Maoz, D., Istrate, A.G. et al. An irradiated-Jupiter analogue hotter than the Sun. Nat Astron 7, 1329–1340 (2023). https://doi.org/10.1038/s41550-023-02048-z

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