KOBE-1: The first planetary system from the KOBE survey

Context . K-dwarf stars are promising targets in the exploration of potentially habitable planets. Their properties, falling between G and M dwarfs, provide an optimal trade-off between the prospect of habitability and ease of detection. The KOBE experiment is a blind-search survey exploiting this niche, monitoring the radial velocity of 50 late-type K-dwarf stars. It employs the CARMENES spectrograph, with an observational strategy designed to detect planets in the habitable zone of their system. Aims . In this work, we exploit the KOBE data set to characterize planetary signals in the K7 V star HIP 5957 (KOBE-1) and to constrain the planetary population within its habitable zone. Methods . We used 82 CARMENES spectra over a time span of three years. We employed a generalized Lomb–Scargle periodogram to search for significant periodic signals that would be compatible with Keplerian motion on KOBE-1. We carried out a model comparison within a Bayesian framework to ensure the significance of the planetary model over alternative configurations of lower complexity. We also inspected two available TESS sectors in search of planetary signals. Results . We identified two signals: at P b = 8.5 d and P c = 29.7 d. We confirmed their planetary nature through ruling out other non-planetary configurations. Their minimum masses are 8.80 ± 0.76 M ⊕ (KOBE-1 b), and 12.4 ± 1.1 M ⊕ (KOBE-1 c), corresponding to absolute masses within the planetary regime at a high certainty (>99.7%). By analyzing the sensitivity of the CARMENES time series to additional signals, we discarded planets above 8.5 M ⊕ within the habitable zone. We identified a single transit-like feature in TESS, whose origin is still uncertain, but still compatible within 1 σ with a transit from planet c. Conclusions . The KOBE-1 multi-planetary system, consisting of a relatively quiet K7-dwarf hosting two sub-Neptune-minimum- mass planets, establishes the first discovery from the KOBE experiment. We have explored future prospects for characterizing this system, concluding that Gaia DR4 will be insensitive to their astrometric signature. Meanwhile, nulling interferometry with the Large Interferometer For Exoplanets (LIFE) mission could be capable of directly imaging both planets and characterizing their atmospheres in future studies.

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Journal
Astronomy and Astrophysics
Published
2025-02-01
DOI
https://doi.org/10.1051/0004-6361/202452631
Citations
4
Primary Topic
Stellar, planetary, and galactic studies
Type
article
Field-Weighted Citation Impact
4.62

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article

KOBE-1: The first planetary system from the KOBE survey

J. Lillo-Box, O. Balsalobre-Ruza, J. F. Agüí Fernández, E. Solano et al.
4 citations
Astronomy and Astrophysics
Stellar, planetary, and galactic studies
4.62
article

KOBE-1: The first planetary system from the KOBE survey

J. Lillo-Box, O. Balsalobre-Ruza, J. F. Agüí Fernández, E. Solano, P. Figueira, A. Fernández-Martín, S. Góngora, A. Guijarro, A. Santerne, Jesús Victoria Flores Salazar, S. Grouffal, J. P. Faria, V. Adibekyan, J. Aceituno, E. Nagel, G. Bergond, M. Azzaro, A. Castro-González, Matthew R. Standing, I. Hermelo, José Ignacio Linares, E. Delgado Mena, S. Cikota, D. Barrado, N. Huélamo, M. Morales‐Calderón, A. Abreu Aramburu, S. C. C. Barros, N. C. Santos, J. C. Morales, C. Cifuentes, A. M. Silva, Á. Berihuete, E. Marfil, Artyom Aguichine, S. G. Sousa, V. Pinter, L. González-Ramírez
article en
4 citations

Abstract

Context . K-dwarf stars are promising targets in the exploration of potentially habitable planets. Their properties, falling between G and M dwarfs, provide an optimal trade-off between the prospect of habitability and ease of detection. The KOBE experiment is a blind-search survey exploiting this niche, monitoring the radial velocity of 50 late-type K-dwarf stars. It employs the CARMENES spectrograph, with an observational strategy designed to detect planets in the habitable zone of their system. Aims . In this work, we exploit the KOBE data set to characterize planetary signals in the K7 V star HIP 5957 (KOBE-1) and to constrain the planetary population within its habitable zone. Methods . We used 82 CARMENES spectra over a time span of three years. We employed a generalized Lomb–Scargle periodogram to search for significant periodic signals that would be compatible with Keplerian motion on KOBE-1. We carried out a model comparison within a Bayesian framework to ensure the significance of the planetary model over alternative configurations of lower complexity. We also inspected two available TESS sectors in search of planetary signals. Results . We identified two signals: at P b = 8.5 d and P c = 29.7 d. We confirmed their planetary nature through ruling out other non-planetary configurations. Their minimum masses are 8.80 ± 0.76 M ⊕ (KOBE-1 b), and 12.4 ± 1.1 M ⊕ (KOBE-1 c), corresponding to absolute masses within the planetary regime at a high certainty (>99.7%). By analyzing the sensitivity of the CARMENES time series to additional signals, we discarded planets above 8.5 M ⊕ within the habitable zone. We identified a single transit-like feature in TESS, whose origin is still uncertain, but still compatible within 1 σ with a transit from planet c. Conclusions . The KOBE-1 multi-planetary system, consisting of a relatively quiet K7-dwarf hosting two sub-Neptune-minimum- mass planets, establishes the first discovery from the KOBE experiment. We have explored future prospects for characterizing this system, concluding that Gaia DR4 will be insensitive to their astrometric signature. Meanwhile, nulling interferometry with the Large Interferometer For Exoplanets (LIFE) mission could be capable of directly imaging both planets and characterizing their atmospheres in future studies.

Astronomy and AstrophysicsVol. 694
University of Geneva (CH), Universidad Complutense de Madrid (ES), Centre National de la Recherche Scientifique (FR), Institute of Space Sciences (ES), University of Lisbon (PT), Universidade do Porto (PT), University of California, Santa Cruz (US), Aix-Marseille Université (FR), Universidad de Cádiz (ES), Calar Alto Observatory (ES), Institute of Astrophysics and Space Sciences (PT), Institut d'Estudis Espacials de Catalunya (ES), European Space Astronomy Centre (ES), Institute of Space Sciences (ES), Centro de Astrobiología (ES), Institut de Ciència de Materials de Barcelona (ES), Instituto de Astrofísica de Andalucía (ES), University of Göttingen (DE), Universidad Politécnica de Madrid (ES), Universitat Politècnica de Catalunya (ES)
National Aeronautics and Space Administration, California Institute of Technology, Aix-Marseille Université, European Space Agency, European Commission, Indian Council of Agricultural Research, Deutsche Forschungsgemeinschaft, Centre National d’Etudes Spatiales, Universidad Complutense de Madrid, Nuclear Safety and Security Commission, Centre National de la Recherche Scientifique, Ministerio de Ciencia e Innovación, Fundação para a Ciência e a Tecnologia, European Regional Development Fund, Agencia Estatal de Investigación, European Social Fund
Openalex Percentile: Top 7%
Stellar, planetary, and galactic studies
4.62
DOIOpen Access PDFOpenAlex
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