Euclid: Quick Data Release (Q1) – Ultracool dwarfs in the Euclid Deep Fields
Astronomy and Astrophysics, vol. 713, pp. A245
Abstract
Ultracool dwarfs (UCDs) encompass the lowest-mass stars and brown dwarfs at the stellar–substellar boundary. These intrinsically faint objects are challenging to detect. However, the wide coverage and deep sensitivity of the Euclid survey will increase the number of confirmed and well-characterised UCDs by several orders of magnitude. We carried out a systematic study using Euclid Quick Data Release (Q1) low-resolution near-infrared (NIR) spectra to identify and characterise UCDs. A sample of previously known UCDs in Q1 was compiled to validate the analysis, which was then applied to newly identified UCD candidates in Euclid Deep Field North (EDF-N; 22.9 deg 2 , down to J E ≈ 24.5 mag). We confirm 33 new UCDs in EDF-N, spanning spectral types (SpTs) M7–T1 ( J E = 17–21 mag) and distances of 50–600 pc. Six of them were also independently identified in other Q1 studies. We followed up on two of these objects with ground-based optical and NIR observations using the Gran Telescopio Canarias, providing an independent validation of the Euclid spectral classification and the ability of Q1 spectra to constrain the stellar parameters of UCDs. We determined the SpTs from Euclid Q1 spectra of 33 newly identified UCDs and 167 previously known UCDs by fitting spectral standards from the SpeX Prism Library Analysis Toolkit. The known UCD sample includes 103 objects in common with the Dark Energy Survey (M7–T0, J E = 17–22 mag, and d = 50–600 pc), 6 objects from literature compilations of UCD sources (M8–T7, J E = 18–20 mag, and d = 30–300 pc), and 58 in common with Gaia (M7–L1, J E = 17–24 mag, and d = 70–300 pc). We derived independent stellar parameter estimates through atmospheric model fitting; the resulting effective temperatures are in good agreement with Euclid SpTs. Combined with complementary ground- and space-based data, these results demonstrate the potential for determining proper motions and identifying companions. Additionally, we investigated Gaia UCDs in Q1 by combining their mean XP spectra with Euclid NIR spectra, extending the wavelength coverage and enabling more comprehensive determinations of stellar parameters, including radii. To support broader classification efforts, we analysed the UCDs in colour–colour space and assessed their separation from quasar loci. We present a publicly available, machine-readable catalogue that includes Euclid observations of known and newly identified sources, with spectral classifications and stellar parameters. This work demonstrates Euclid ’s capability to identify and characterise the faintest stellar populations, establishing a foundation for large-scale UCD studies with forthcoming survey data.
Authors 99
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Centre National de la Recherche Scientifique · Institut UTINAM · Observatoire des Sciences de l’Univers Terre Homme Environnement Temps Astronomie · Université Marie et Louis Pasteur
Affiliation as printed
Université Marie et Louis Pasteur, CNRS, Observatoire des Sciences de l’Univers THETA Franche-Comté Bourgogne, Institut UTINAM
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University of Hertfordshire · Osservatorio Astrofisico di Torino · National Institute for Astrophysics
Affiliation as printed
Department of Physics, Astronomy and Mathematics, University of Hertfordshire
INAF – Osservatorio Astrofisico di Torino
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Centre National de la Recherche Scientifique · Institut UTINAM · Observatoire des Sciences de l’Univers Terre Homme Environnement Temps Astronomie · Université Marie et Louis Pasteur
Affiliation as printed
Université Marie et Louis Pasteur, CNRS, Observatoire des Sciences de l’Univers THETA Franche-Comté Bourgogne, Institut UTINAM
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Centre National de la Recherche Scientifique · Aix-Marseille Université
Affiliation as printed
Aix-Marseille Université, CNRS, CNES, LAM
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Universidad Politécnica de Cartagena
Affiliation as printed
Departamento Física Aplicada, Universidad Politécnica de Cartagena, Campus Muralla del Mar
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Max Planck Institute for Astronomy
Affiliation as printed
Max-Planck-Institut für Astronomie
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Affiliation as printed
Department of Physics, Astronomy and Mathematics, University of Hertfordshire
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International Space University · International Space University
Affiliation as printed
International Space University
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Centre National de la Recherche Scientifique · University of Leicester · Observatoire astronomique de Strasbourg · Université de Strasbourg
Affiliation as printed
School of Physics and Astronomy, University of Leicester
Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg
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Affiliation as printed
Centro de Astrobiología (CAB), CSIC-INTA, ESAC Campus, Camino Bajo del Castillo s/n
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Royal Observatory · University of Edinburgh
Affiliation as printed
Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill
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European Southern Observatory · European Southern Observatory
Affiliation as printed
European Southern Observatory
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Universidad de La Laguna · Instituto de Astrofísica de Canarias
Affiliation as printed
Instituto de Astrofísica de Canarias
Universidad de La Laguna, Dpto. Astrofísica
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Universidad de La Laguna · Instituto de Astrofísica de Canarias
Affiliation as printed
Instituto de Astrofísica de Canarias
Universidad de La Laguna, Dpto. Astrofísica
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Universidad de La Laguna · Instituto de Astrofísica de Canarias
Affiliation as printed
Instituto de Astrofísica de Canarias
Universidad de La Laguna, Dpto. Astrofísica
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Universidad de La Laguna · Instituto de Astrofísica de Canarias
Affiliation as printed
Instituto de Astrofísica de Canarias
Universidad de La Laguna, Dpto. Astrofísica
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Affiliation as printed
Centro de Astrobiología (CAB), CSIC-INTA, ESAC Campus, Camino Bajo del Castillo s/n
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Universidad de La Laguna · Instituto de Astrofísica de Canarias
Affiliation as printed
Instituto de Astrofísica de Canarias, 38205 La Laguna; Universidad de La Laguna, Dpto. Astrofísica
Universidad de La Laguna, Dpto. Astrofísica
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Affiliation as printed
Centro de Astrobiología (CAB), CSIC-INTA, ESAC Campus, Camino Bajo del Castillo s/n
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Astronomical Observatory of Capodimonte · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio Astronomico di Capodimonte
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Consejo Superior de Investigaciones Científicas · Universidad de La Laguna · Instituto de Astrofísica de Canarias
Affiliation as printed
Consejo Superior de Investigaciones Cientificas
Instituto de Astrofísica de Canarias
Universidad de La Laguna, Dpto. Astrofísica
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Royal Observatory · University of Edinburgh
Affiliation as printed
Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill
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Universidad de La Laguna · Instituto de Astrofísica de Canarias
Affiliation as printed
Instituto de Astrofísica de Canarias
Universidad de La Laguna, Dpto. Astrofísica
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Centre National de la Recherche Scientifique · Université Paris-Saclay · Institut d'Astrophysique Spatiale
Affiliation as printed
Université Paris-Saclay, CNRS, Institut d’astrophysique spatiale
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European Space Agency · European Space Astronomy Centre
Affiliation as printed
European Space Agency/ESAC, Camino Bajo del Castillo, s/n., Urb. Villafranca del Castillo
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Affiliation as printed
School of Mathematics and Physics, University of Surrey, Guildford
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Brera Astronomical Observatory · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio Astronomico di Brera
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Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna
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Scuola Internazionale Superiore di Studi Avanzati · Trieste Astronomical Observatory · Istituto Nazionale di Fisica Nucleare, Sezione di Trieste · Institute for Fundamental Physics of the Universe · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio Astronomico di Trieste
INFN, Sezione di Trieste
Institute for Fundamental Physics of the Universe (IFPU)
SISSA, International School for Advanced Studies
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Istituto Nazionale di Fisica Nucleare, Sezione di Bologna · Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics · University of Bologna
Affiliation as printed
Dipartimento di Fisica e Astronomia, Università di Bologna
INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna
INFN-Sezione di Bologna
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Osservatorio Astronomico di Padova · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio Astronomico di Padova
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Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna
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Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna
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Trieste Astronomical Observatory · Institute for Fundamental Physics of the Universe · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio Astronomico di Trieste
Institute for Fundamental Physics of the Universe (IFPU)
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Affiliation as printed
Space Science Data Center, Italian Space Agency, via del Politecnico snc
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Brera Astronomical Observatory · Istituto Nazionale di Fisica Nucleare, Sezione di Genova · University of Genoa · National Institute for Astrophysics
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Dipartimento di Fisica, Università di Genova
INAF-Osservatorio Astronomico di Brera
INFN-Sezione di Genova
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Astronomical Observatory of Capodimonte · University of Naples Federico II · National Institute for Astrophysics
Affiliation as printed
Department of Physics “E. Pancini”, University Federico II
INAF-Osservatorio Astronomico di Capodimonte
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Universidade do Porto · Institute of Astrophysics and Space Sciences · Centro de Astrofísica da Universidade do Porto
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Faculdade de Ciências da Universidade do Porto, Rua do Campo de Alegre
Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas
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Istituto Nazionale di Fisica Nucleare, Sezione di Torino · Osservatorio Astrofisico di Torino · University of Turin · National Institute for Astrophysics
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Dipartimento di Fisica, Università degli Studi di Torino
INAF – Osservatorio Astrofisico di Torino
INFN-Sezione di Torino
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Leiden University · European Space Agency · Leiden Observatory · European Space Research and Technology Centre
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European Space Agency/ESTEC
Institute Lorentz, Leiden University
Leiden Observatory, Leiden University
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Osservatorio Astrofisico di Torino · National Institute for Astrophysics
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INAF – Osservatorio Astrofisico di Torino
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National Institute for Astrophysics
Affiliation as printed
INAF-IASF Milano
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Port d'Informació Científica · Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas
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Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT)
Port d’Informació Científica, Campus UAB, c. Albareda s/n
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Affiliation as printed
Institut für Theoretische Teilchenphysik und Kosmologie (TTK), RWTH Aachen University
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Astronomical Observatory of Rome · National Institute for Astrophysics
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INAF-Osservatorio Astronomico di Roma
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Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna
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Istituto Nazionale di Fisica Nucleare · Astronomical Observatory of Capodimonte · Istituto Nazionale di Fisica Nucleare, Sezione di Napoli · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio Astronomico di Capodimonte
INFN section of Naples
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University of Hawaiʻi at Mānoa · University of Hawaii System
Affiliation as printed
Institute for Astronomy, University of Hawaii
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Affiliation as printed
Dipartimento di Fisica e Astronomia “Augusto Righi”, Alma Mater Studiorum Università di Bologna
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Instituto de Astrofísica de Canarias
Affiliation as printed
Instituto de Astrofísica de Canarias
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Royal Observatory · University of Edinburgh
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Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill
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Affiliation as printed
Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, University of Manchester
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European Space Agency · European Space Astronomy Centre · European Space Research Institute
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European Space Agency/ESAC, Camino Bajo del Castillo, s/n., Urb. Villafranca del Castillo
European Space Agency/ESRIN
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Lyon 1 Université · Centre National de la Recherche Scientifique · Institut National de Physique Nucléaire et de Physique des Particules · Institut de Physique des 2 Infinis de Lyon
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Université Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, UMR 5822
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Centre National de la Recherche Scientifique · Aix-Marseille Université
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Aix-Marseille Université, CNRS, CNES, LAM
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Institució Catalana de Recerca i Estudis Avançats · Institut de Ciències del Cosmos · Universitat de Barcelona
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Institució Catalana de Recerca i Estudis Avançats (ICREA)
Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB)
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Lyon 1 Université · Centre National de la Recherche Scientifique · Institut National de Physique Nucléaire et de Physique des Particules · Institut de Physique des 2 Infinis de Lyon
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Université Claude Bernard Lyon 1 (UCBL), CNRS/IN2P3, IUF, IP2I Lyon
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Affiliation as printed
Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking
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University of Lisbon · Institute of Astrophysics and Space Sciences
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Departamento de Física, Faculdade de Ciências, Universidade de Lisboa
Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências, Universidade de Lisboa
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Département d’astronomie, Université de Genève,
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Trieste Astronomical Observatory · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio Astronomico di Trieste
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Centre National de la Recherche Scientifique · Université Paris-Saclay · Institut d'Astrophysique Spatiale
Affiliation as printed
Université Paris-Saclay, CNRS, Institut d’astrophysique spatiale
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Centre National de la Recherche Scientifique · Université Paris-Saclay · Institut d'Astrophysique Spatiale
Affiliation as printed
Université Paris-Saclay, CNRS, Institut d’astrophysique spatiale
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Affiliation as printed
Département d’astronomie, Université de Genève,
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European Space Agency · European Space Astronomy Centre
Affiliation as printed
European Space Agency/ESAC, Camino Bajo del Castillo, s/n., Urb. Villafranca del Castillo
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Istituto Nazionale di Fisica Nucleare · Istituto Nazionale di Fisica Nucleare, Sezione di Padova
Affiliation as printed
INFN-Padova
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Centre National de la Recherche Scientifique · Aix-Marseille Université · Centre de physique des particules de Marseille · Institut National de Physique Nucléaire et de Physique des Particules
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Aix-Marseille Université, CNRS/IN2P3, CPPM
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Institute for Space Astrophysics and Planetology · National Institute for Astrophysics
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INAF-Istituto di Astrofisica e Planetologia Spaziali
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Astronomical Observatory of Rome · Agenzia Spaziale Italiana · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio Astronomico di Roma
Space Science Data Center, Italian Space Agency, via del Politecnico snc
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Lyon 1 Université · Centre National de la Recherche Scientifique · Institut National de Physique Nucléaire et de Physique des Particules · Institut de Physique des 2 Infinis de Lyon
Affiliation as printed
Université Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, UMR 5822
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Affiliation as printed
School of Physics, HH Wills Physics Laboratory, University of Bristol
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Trieste Astronomical Observatory · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio Astronomico di Trieste
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Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna
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Trieste Astronomical Observatory · National Institute for Astrophysics
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INAF-Osservatorio Astronomico di Trieste
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Ludwig-Maximilians-Universität München
Affiliation as printed
Universitäts-Sternwarte München, Fakultät für Physik, Ludwig-Maximilians-Universität München
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Centre National de la Recherche Scientifique · Aix-Marseille Université · Centre de physique des particules de Marseille · Institut National de Physique Nucléaire et de Physique des Particules
Affiliation as printed
Aix-Marseille Université, CNRS/IN2P3, CPPM
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Royal Observatory · University of Edinburgh
Affiliation as printed
Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill
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Istituto Nazionale di Fisica Nucleare, Sezione di Bologna · Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna
INFN-Sezione di Bologna
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Max Planck Institute for Extraterrestrial Physics
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Max-Planck-Institut für extraterrestrische Physik
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Brera Astronomical Observatory · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio Astronomico di Brera
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Osservatorio Astronomico di Padova · National Institute for Astrophysics
Affiliation as printed
INAF-Osservatorio Astronomico di Padova
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Max Planck Institute for Extraterrestrial Physics · Ludwig-Maximilians-Universität München
Affiliation as printed
Max-Planck-Institut für extraterrestrische Physik
Universitäts-Sternwarte München, Fakultät für Physik, Ludwig-Maximilians-Universität München
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Affiliation as printed
Institutt for teoretisk astrofysikk, University of Oslo
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European Space Agency · European Space Astronomy Centre
Affiliation as printed
European Space Agency/ESAC, Camino Bajo del Castillo, s/n., Urb. Villafranca del Castillo
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Affiliation as printed
Jet Propulsion Laboratory, California Institute of Technology
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Affiliation as printed
Felix Hormuth Engineering
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Technical University of Denmark
Affiliation as printed
Cosmic Dawn Center (DAWN)
Danmarks Tekniske Universitet
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Max Planck Institute for Astronomy
Affiliation as printed
Max-Planck-Institut für Astronomie
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Affiliation as printed
NASA Goddard Space Flight Center
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Affiliation as printed
Department of Physics and Helsinki Institute of Physics
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Centre National de la Recherche Scientifique · Aix-Marseille Université · Centre de physique des particules de Marseille · Institut National de Physique Nucléaire et de Physique des Particules
Affiliation as printed
Aix-Marseille Université, CNRS/IN2P3, CPPM
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Affiliation as printed
Jet Propulsion Laboratory, California Institute of Technology
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Lyon 1 Université · Centre National de la Recherche Scientifique · Institut National de Physique Nucléaire et de Physique des Particules · Institut de Physique des 2 Infinis de Lyon
Affiliation as printed
Université Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, UMR 5822
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University
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Ludwig-Maximilians-Universität München
Affiliation as printed
Universitäts-Sternwarte München, Fakultät für Physik, Ludwig-Maximilians-Universität München
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Affiliation as printed
Université de Genève, Département de Physique Théorique and Centre for Astroparticle Physics
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Affiliation as printed
Department of Physics
Helsinki Institute of Physics
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Centre National de la Recherche Scientifique · Centre de Calcul de l’Institut National de Physique Nucléaire et de Physique des Particules
Affiliation as printed
Centre de Calcul de l’IN2P3/CNRS
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Centre National de la Recherche Scientifique · Université Paris Sciences et Lettres · Observatoire de Paris · Sorbonne Université · Laboratoire d'Étude de l'Univers et des Phénomènes Extrêmes
Affiliation as printed
Laboratoire d’etude de l’Univers et des phenomenes eXtremes, Observatoire de Paris, Université PSL, Sorbonne Université, CNRS
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