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Transit detection of the long-period volatile-rich super-Earth ν2 Lupi d with CHEOPS

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Abstract

Exoplanets transiting bright nearby stars are key objects for advancing our knowledge of planetary formation and evolution. The wealth of photons from the host star gives detailed access to the atmospheric, interior and orbital properties of the planetary companions. ν2 Lupi (HD 136352) is a naked-eye (V = 5.78) Sun-like star that was discovered to host three low-mass planets with orbital periods of 11.6, 27.6 and 107.6 d via radial-velocity monitoring1. The two inner planets (b and c) were recently found to transit2, prompting a photometric follow-up by the brand new Characterising Exoplanets Satellite (CHEOPS). Here, we report that the outer planet d is also transiting, and measure its radius and mass to be 2.56 ± 0.09 R and 8.82 ± 0.94 M, respectively. With its bright Sun-like star, long period and mild irradiation (~5.7 times the irradiation of Earth), ν2 Lupi d unlocks a completely new region in the parameter space of exoplanets amenable to detailed characterization. We refine the properties of all three planets: planet b probably has a rocky mostly dry composition, while planets c and d seem to have retained small hydrogen–helium envelopes and a possibly large water fraction. This diversity of planetary compositions makes the ν2 Lupi system an excellent laboratory for testing formation and evolution models of low-mass planets.

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Fig. 1: CHEOPS transit photometry of the ν2 Lupi planets.
Fig. 2: The ν2 Lupi planets in the context of other known transiting exoplanets.
Fig. 3: Internal structures of the ν2 Lupi planets.

Data availability

The CHEOPS light curves used in this work will be made available for download at the CDS (Centre de Données astronomiques de Strasbourg). We will provide both the raw and detrended light curves. All other data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

Code availability

The CHEOPS DRP is built over several public Python libraries, such as Astropy148,149, NumPy150 and SciPy151. The TESS light curve was extracted using the lightkurve31 open-source Python package. The data analysis was performed using the juliet Python library, which is also publicly available. The figures were produced using the Matplotlib152 and corner153 open-source Python modules. The codes used in this work are available upon reasonable request from the corresponding author.

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Acknowledgements

CHEOPS is a European Space Agency (ESA) mission in partnership with Switzerland with important contributions to the payload and the ground segment from Austria, Belgium, France, Germany, Hungary, Italy, Portugal, Spain, Sweden and the United Kingdom. The Swiss participation in CHEOPS has been supported by the Swiss Space Office in the framework of PRODEX and the Activités Nationales Complémentaires and the Universities of Bern and Geneva as well as the NCCR PlanetS and the Swiss National Science Foundation. The MOC activities have been supported by ESA contract 4000124370. S.C. acknowledges financial support by LabEx UnivEarthS (ANR-10-LABX-0023 and ANR-18-IDEX-0001). This work was supported by FCT (Fundação para a Ciência e a Tecnologia) through national funds and by FEDER (Fundo Europeu de Desenvolvimento Regional) through COMPETE2020—Programa Operacional Competitividade e Internacionalização with these grants: UID/FIS/04434/2019; UIDB/04434/2020; UIDP/04434/2020; PTDC/FIS-AST/32113/2017 and POCI-01-0145-FEDER-032113; PTDC/FIS-AST/28953/2017 and POCI-01-0145-FEDER-028953; PTDC/FIS-AST/28987/2017 and POCI-01-0145-FEDER-028987. S.C.C.B., S.G.S. and V.A. acknowledge support from FCT through contracts IF/01312/2014/CP1215/CT0004, CEECIND/00826/2018, POPH/FSE (EC) and IF/00650/2015/CP1273/CT0001. O.D.S.D. is supported in the form of a work contract (DL 57/2016/CP1364/CT0004) with national funds through FCT. M.J.H. acknowledges the support of the Swiss National Fund under grant 200020_172746. A.D. and D.E. acknowledge support from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (project Four Aces; grant agreement 724427). S.H. acknowledges CNES funding through grant 837319. The Spanish scientific participation in CHEOPS has been supported by the Spanish Ministry of Science and Innovation and the European Regional Development Fund through grants ESP2016-80435-C2-1-R, ESP2016-80435-C2-2-R, ESP2017-87676-C5-1-R, PGC2018-098153-B-C31, PGC2018-098153-B-C33 and MDM-2017-0737 Unidad de Excelencia María de Maeztu–Centro de Astrobiología (INTA-CSIC), as well as by the Generalitat de Catalunya/CERCA programme. The Belgian participation in CHEOPS has been supported by the Belgian Federal Science Policy Office in the framework of the PRODEX Programme of the ESA under contract PEA 4000131343, and by the University of Liège through an ARC grant for Concerted Research Actions financed by the Wallonia–Brussels Federation. L.D. is an FRS-FNRS Postdoctoral Researcher. M. Gillon is an FRS–FNRS Senior Research Associate. V.V.G. is an FRS–FNRS Research Associate. M.L. acknowledges support from the Austrian Research Promotion Agency (FFG) under project 859724 ‘GRAPPA’. B.-O.D. acknowledges support from the Swiss National Science Foundation (PP00P2-190080). S. Salmon has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant agreement 833925, project STAREX). G.M.S. acknowledges funding from the Hungarian National Research, Development and Innovation Office (NKFIH) grant GINOP-2.3.2-15-2016-00003 and K-119517. For Italy, CHEOPS activities have been supported by the Italian Space Agency, under the programmes ASI-INAF 2013-016-R.0 and ASI-INAF 2019-29-HH.0. L.B., G.P., I.P., G.S. and V.N. acknowledge funding support from the Italian Space Agency (ASI) regulated by ‘Accordo ASI-INAF 2013-016-R.0 del 9 luglio 2013 e integrazione del 9 luglio 2015’. A.C.C. and T.G.W. acknowledge support from STFC consolidated grant ST/M001296/1. D.G., X.B., S.C., M.F. and J.L. acknowledge their roles as ESA-appointed CHEOPS science team members. We thank S. R. Kane for sharing some RV data before their publication and L. D. Nielsen for helping to plan the CHEOPS observations on the basis of her analysis of the TESS data. We also thank M. Cretignier for his independent analysis of the HARPS RV data.

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L.D. led the data analysis, with support from L.B., M.J.H., S.H., A. Brandeker, A.D., P.G., N.H., M.O. and T.G.W. L.D. also coordinated the interpretation of the results and writing of the manuscript. D.E. designed and coordinated, with support from A.D., the CHEOPS Early Science programme, within which these observations took place. Y.A. led the analysis of the internal structures, with support from J.H., A. Bonfanti and L.F. performed the atmospheric evolution simulations. L.B. carried out the TTV simulations. F.J.P. studied the orbital stability and tidal interactions. S. Salmon, V.A., A. Bonfanti, S.G.S., V.V.G. and T.G.W. performed the stellar characterization. S. Sulis analysed the stellar granulation and oscillations. V.B. assessed the potential of the system for atmospheric characterization. S.C. evaluated the possibility of ν2 Lupi d having moons or rings. The other authors provided key contributions to the development of the CHEOPS mission. All authors read and commented on the manuscript, and helped with its revision.

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Correspondence to Laetitia Delrez.

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Delrez, L., Ehrenreich, D., Alibert, Y. et al. Transit detection of the long-period volatile-rich super-Earth ν2 Lupi d with CHEOPS. Nat Astron 5, 775–787 (2021). https://doi.org/10.1038/s41550-021-01381-5

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