Refined parameters of the HD 22946 planetary system and the true orbital period of planet d

Z. Garai; H. P. Osborn; D. Gandolfi; A. Brandeker; S. G. Sousa; M. Lendl; A. Bekkelien; C. Broeg; A. Collier Cameron; J. A. Egger; M. J. Hooton; Y. Alibert; L. Delrez; L. Fossati; S. Salmon; T. G. Wilson; A. Bonfanti; A. Tuson; S. Ulmer-Moll; L. M. Serrano; L. Borsato; R. Alonso; G. Anglada; J. Asquier; D. Barrado y Navascues; S. C. C. Barros; T. Bárczy; W. Baumjohann; M. Beck; T. Beck; W. Benz; N. Billot; F. Biondi; X. Bonfils; M. Buder; J. Cabrera; V. Cessa; S. Charnoz; Sz. Csizmadia; P. E. Cubillos; M. B. Davies; M. Deleuil; O. D. S. Demangeon; B.-O. Demory; D. Ehrenreich; A. Erikson; V. Van Eylen; A. Fortier; M. Fridlund; M. Gillon; V. Van Grootel; M. Güdel; M. N. Günther; S. Hoyer; K. G. Isaak; L. L. Kiss; M. H. Kristiansen; J. Laskar; A. Lecavelier des Etangs; C. Lovis; A. Luntzer; D. Magrin; P. F. L. Maxted; C. Mordasini; V. Nascimbeni; G. Olofsson; R. Ottensamer; I. Pagano; E. Pallé; G. Peter; G. Piotto; D. Pollacco; D. Queloz; R. Ragazzoni; N. Rando; H. Rauer; I. Ribas; N. C. Santos; G. Scandariato; D. Ségransan; A. E. Simon; A. M. S. Smith; M. Steller; Gy. M. Szabó; N. Thomas; S. Udry; J. Venturini; N. Walton

doi:10.1051/0004-6361/202345943

Refined parameters of the HD 22946 planetary system and the true orbital period of planet d

Z. Garai^*, H. P. Osborn, D. Gandolfi, A. Brandeker, S. G. Sousa, M. Lendl, A. Bekkelien, C. Broeg, A. Collier Cameron, J. A. Egger, M. J. Hooton, Y. Alibert, L. Delrez, L. Fossati, S. Salmon, T. G. Wilson, A. Bonfanti, A. Tuson, S. Ulmer-Moll, L. M. SerranoL. Borsato, R. Alonso, G. Anglada, J. Asquier, D. Barrado y Navascues, S. C. C. Barros, T. Bárczy, W. Baumjohann, M. Beck, T. Beck, W. Benz, N. Billot, F. Biondi, X. Bonfils, M. Buder, J. Cabrera, V. Cessa, S. Charnoz, Sz. Csizmadia, P. E. Cubillos, M. B. Davies, M. Deleuil, O. D. S. Demangeon, B.-O. Demory, D. Ehrenreich, A. Erikson, V. Van Eylen, A. Fortier, M. Fridlund, M. Gillon, V. Van Grootel, M. Güdel, M. N. Günther, S. Hoyer, K. G. Isaak, L. L. Kiss, M. H. Kristiansen, J. Laskar, A. Lecavelier des Etangs, C. Lovis, A. Luntzer, D. Magrin, P. F. L. Maxted, C. Mordasini, V. Nascimbeni, G. Olofsson, R. Ottensamer, I. Pagano, E. Pallé, G. Peter, G. Piotto, D. Pollacco, D. Queloz, R. Ragazzoni, N. Rando, H. Rauer, I. Ribas, N. C. Santos, G. Scandariato, D. Ségransan, A. E. Simon, A. M. S. Smith, M. Steller, Gy. M. Szabó, N. Thomas, S. Udry, J. Venturini, N. Walton

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

Abstract

Context. Multi-planet systems are important sources of information regarding the evolution of planets. However, the long-period planets in these systems often escape detection. These objects in particular may retain more of their primordial characteristics compared to close-in counterparts because of their increased distance from the host star. HD 22946 is a bright (G = 8.13 mag) late F-type star around which three transiting planets were identified via Transiting Exoplanet Survey Satellite (TESS) photometry, but the true orbital period of the outermost planet d was unknown until now.

Aims. We aim to use the Characterising Exoplanet Satellite (CHEOPS) space telescope to uncover the true orbital period of HD 22946d and to refine the orbital and planetary properties of the system, especially the radii of the planets.

Methods. We used the available TESS photometry of HD 22946 and observed several transits of the planets b, c, and d using CHEOPS. We identified two transits of planet d in the TESS photometry, calculated the most probable period aliases based on these data, and then scheduled CHEOPS observations. The photometric data were supplemented with ESPRESSO (Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations) radial velocity data. Finally, a combined model was fitted to the entire dataset in order to obtain final planetary and system parameters.

Results. Based on the combined TESS and CHEOPS observations, we successfully determined the true orbital period of the planet d to be 47.42489 ± 0.00011 days, and derived precise radii of the planets in the system, namely 1.362 ± 0.040 R_⊕, 2.328 ± 0.039 R_⊕, and 2.607 ± 0.060 R_⊕ for planets b, c, and d, respectively. Due to the low number of radial velocities, we were only able to determine 3σ upper limits for these respective planet masses, which are 13.71 M_⊕, 9.72 M_⊕, and 26.57 M_⊕. We estimated that another 48 ESPRESSO radial velocities are needed to measure the predicted masses of all planets in HD 22946. We also derived stellar parameters for the host star.

Conclusions. Planet c around HD 22946 appears to be a promising target for future atmospheric characterisation via transmission spectroscopy. We can also conclude that planet d, as a warm sub-Neptune, is very interesting because there are only a few similar confirmed exoplanets to date. Such objects are worth investigating in the near future, for example in terms of their composition and internal structure.

Original language	English
Article number	A44
Number of pages	14
Journal	Astronomy & Astrophysics
Volume	674
DOIs	https://doi.org/10.1051/0004-6361/202345943
Publication status	Published - 8 Jun 2023

Keywords

Methods: observational
Techniques: photometric
Planets and satellites: fundamental parameters

Access to Document

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Garai_2023_AaA_Refined-parameters-HD-22946-planetary-system_CC
© The Authors 2023. Open Access article published under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Final published version, 1.27 MBLicence: CC BY

https://arxiv.org/abs/2306.04468

Astronomy at St Andrews 2018-2021: Astronomy at St Andrews 2018-2021
Jardine, M. (PI), Bonnell, I. (CoI), Cameron, A. (CoI), Cyganowski, C. (CoI), Dominik, M. (CoI), Helling, C. (CoI), Horne, K. (CoI), Scholz, A. (CoI), Tojeiro, R. (CoI), Weijmans, A.-M. (CoI), Wild, V. (CoI), Woitke, P. (CoI), Wood, K. (CoI) & Zhao, H. (CoI)
1/04/18 → 31/03/22
Project: Standard
Support for the PLATO Development: Support for the PLATO Development Phase 2017-2022: Planet candidate ranking and validation
Cameron, A. (PI)
Science & Technology Facilities Council
1/08/17 → 31/12/22
Project: Standard

TESS, CHEOPS and ESPRESSO data of HD 22946 : J/A+A/674/A44
Cameron, A. (Creator) & Wilson, T. (Creator), VizieR On-line Data Catalog, 2025
DOI: 10.26093/cds/vizier.36740044
Dataset

Cite this

Garai, Z., Osborn, H. P., Gandolfi, D., Brandeker, A., Sousa, S. G., Lendl, M., Bekkelien, A., Broeg, C., Cameron, A. C., Egger, J. A., Hooton, M. J., Alibert, Y., Delrez, L., Fossati, L., Salmon, S., Wilson, T. G., Bonfanti, A., Tuson, A., Ulmer-Moll, S., ... Walton, N. (2023). Refined parameters of the HD 22946 planetary system and the true orbital period of planet d. Astronomy & Astrophysics, 674, Article A44. https://doi.org/10.1051/0004-6361/202345943

@article{99964f9edd6549369ac3f01a158c7e7e,

title = "Refined parameters of the HD 22946 planetary system and the true orbital period of planet d",

abstract = "Context. Multi-planet systems are important sources of information regarding the evolution of planets. However, the long-period planets in these systems often escape detection. These objects in particular may retain more of their primordial characteristics compared to close-in counterparts because of their increased distance from the host star. HD 22946 is a bright (G = 8.13 mag) late F-type star around which three transiting planets were identified via Transiting Exoplanet Survey Satellite (TESS) photometry, but the true orbital period of the outermost planet d was unknown until now. Aims. We aim to use the Characterising Exoplanet Satellite (CHEOPS) space telescope to uncover the true orbital period of HD 22946d and to refine the orbital and planetary properties of the system, especially the radii of the planets. Methods. We used the available TESS photometry of HD 22946 and observed several transits of the planets b, c, and d using CHEOPS. We identified two transits of planet d in the TESS photometry, calculated the most probable period aliases based on these data, and then scheduled CHEOPS observations. The photometric data were supplemented with ESPRESSO (Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations) radial velocity data. Finally, a combined model was fitted to the entire dataset in order to obtain final planetary and system parameters. Results. Based on the combined TESS and CHEOPS observations, we successfully determined the true orbital period of the planet d to be 47.42489 ± 0.00011 days, and derived precise radii of the planets in the system, namely 1.362 ± 0.040 R⊕, 2.328 ± 0.039 R⊕, and 2.607 ± 0.060 R⊕ for planets b, c, and d, respectively. Due to the low number of radial velocities, we were only able to determine 3σ upper limits for these respective planet masses, which are 13.71 M⊕, 9.72 M⊕, and 26.57 M⊕. We estimated that another 48 ESPRESSO radial velocities are needed to measure the predicted masses of all planets in HD 22946. We also derived stellar parameters for the host star. Conclusions. Planet c around HD 22946 appears to be a promising target for future atmospheric characterisation via transmission spectroscopy. We can also conclude that planet d, as a warm sub-Neptune, is very interesting because there are only a few similar confirmed exoplanets to date. Such objects are worth investigating in the near future, for example in terms of their composition and internal structure.",

keywords = "Methods: observational, Techniques: photometric, Planets and satellites: fundamental parameters",

author = "Z. Garai and Osborn, \{H. P.\} and D. Gandolfi and A. Brandeker and Sousa, \{S. G.\} and M. Lendl and A. Bekkelien and C. Broeg and Cameron, \{A. Collier\} and Egger, \{J. A.\} and Hooton, \{M. J.\} and Y. Alibert and L. Delrez and L. Fossati and S. Salmon and Wilson, \{T. G.\} and A. Bonfanti and A. Tuson and S. Ulmer-Moll and Serrano, \{L. M.\} and L. Borsato and R. Alonso and G. Anglada and J. Asquier and Navascues, \{D. Barrado y\} and Barros, \{S. C. C.\} and T. B{\'a}rczy and W. Baumjohann and M. Beck and T. Beck and W. Benz and N. Billot and F. Biondi and X. Bonfils and M. Buder and J. Cabrera and V. Cessa and S. Charnoz and Sz. Csizmadia and Cubillos, \{P. E.\} and Davies, \{M. B.\} and M. Deleuil and Demangeon, \{O. D. S.\} and B.-O. Demory and D. Ehrenreich and A. Erikson and Eylen, \{V. Van\} and A. Fortier and M. Fridlund and M. Gillon and Grootel, \{V. Van\} and M. G{\"u}del and G{\"u}nther, \{M. N.\} and S. Hoyer and Isaak, \{K. G.\} and Kiss, \{L. L.\} and Kristiansen, \{M. H.\} and J. Laskar and Etangs, \{A. Lecavelier des\} and C. Lovis and A. Luntzer and D. Magrin and Maxted, \{P. F. L.\} and C. Mordasini and V. Nascimbeni and G. Olofsson and R. Ottensamer and I. Pagano and E. Pall{\'e} and G. Peter and G. Piotto and D. Pollacco and D. Queloz and R. Ragazzoni and N. Rando and H. Rauer and I. Ribas and Santos, \{N. C.\} and G. Scandariato and D. S{\'e}gransan and Simon, \{A. E.\} and Smith, \{A. M. S.\} and M. Steller and Szab{\'o}, \{Gy. M.\} and N. Thomas and S. Udry and J. Venturini and N. Walton",

note = "Funding: Z.G. acknowledges the support of the Hungarian National Research, Development and Innovation Office (NKFIH) grant K-125015, the PRODEX Experiment Agreement No. 4000137122 between the ELTE E{\"o}tv{\"o}s Lor{\'a}nd University and the European Space Agency (ESA-D/SCI-LE-2021-0025), the VEGA grant of the Slovak Academy of Sciences No. 2/0031/22, the Slovak Research and Development Agency contract No. APVV-20-0148, and the support of the city of Szombathely. Gy.M.Sz. acknowledges the support of the Hungarian National Research, Development and Innovation Office (NKFIH) grant K-125015, a PRODEX Institute Agreement between the ELTE E{\"o}tv{\"o}s Lor{\'a}nd University and the European Space Agency (ESA-D/SCI-LE-2021-0025), the Lend{\"u}let LP2018-7/2021 grant of the Hungarian Academy of Science and the support of the city of Szombathely. A.Br. was supported by the SNSA. A.C.C. acknowledges support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1. B.-O.D. acknowledges support from the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number MB22.00046. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (project FOUR ACES; grant agreement No 724427). It has also been carried out in the frame of the National Centre for Competence in Research PlanetS supported by the Swiss National Science Foundation (SNSF). D.E. acknowledges financial support from the Swiss National Science Foundation for project 200021\_200726. D.G. gratefully acknowledges financial support from the CRT foundation under Grant No. 2018.2323 “Gaseousor rocky? Unveiling the nature of small worlds”. This work was also partially supported by a grant from the Simons Foundation (PI Queloz, grant number 327127). This work has been carried out within the framework of the NCCR PlanetS supported by the Swiss National Science Foundation under grants 51NF40\_182901 and 51NF40\_205606. I.R.I. acknowledges support from the Spanish Ministry of Science and Innovation and the European Regional Development Fund through grant PGC2018-098153-B-C33, as well as the support of the Generalitat de Catalunya/CERCA programme. L.D. is an F.R.S.-FNRS Postdoctoral Researcher. L.M.S. gratefully acknowledges financial support from the CRT foundation under Grant No. 2018.2323 “Gaseous or rocky? Unveiling the nature of small worlds”. This project was supported by the CNES. M.F. and C.M.P. gratefully acknowledge the support of the Swedish National Space Agency (DNR 65/19, 174/18). M.G. is an F.R.S.-FNRS Senior Research Associate. M.L. acknowledges support of the Swiss National Science Foundation under grant number PCEFP2\_194576. N.A.W. acknowledges UKSA grant ST/R004838/1. This work was supported by FCT – Funda{\c c}{\~a}o para a Ci{\^e}ncia e a Tecnologia through national funds and by FEDER through COMPETE2020 – Programa Operacional Competitividade e Internacionalizac{\~a}o by these grants: UID/FIS/04434/2019, UIDB/04434/2020, UIDP/04434/2020, PTDC/FIS-AST/32113/2017 \& POCI-01-0145-FEDER-032113, PTDC/FIS-AST/28953/2017 \& POCI-01-0145-FEDER-028953, PTDC/FIS-AST/28987/2017 \& POCI-01-0145-FEDER-028987, O.D.S.D. is supported in the form of work contract (DL 57/2016/CP1364/CT0004) funded by national funds through FCT. P.M. acknowledges support from STFC research grant number ST/M001040/1. We acknowledge support from 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, PGC2018-098153-B-C33, PGC2018-098153-B-C31, ESP2017-87676-C5-1-R, MDM-2017-0737 Unidad de Excelencia Maria de Maeztu-Centro de Astrobiolog{\'i}a (INTA-CSIC), as well as the support of the Generalitat de Catalunya/CERCA programme. The MOC activities have been supported by the ESA contract No. 4000124370. S.H. gratefully acknowledges CNES funding through the grant 837319. S.C.C.B. acknowledges support from FCT through FCT contracts nr. IF/01312/2014/CP1215/CT0004. S.G.S. acknowledges support from FCT through FCT contract no. CEECIND/00826/2018 and POPH/FSE (EC). A.C.C. and T.W. acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1. V.V.G. is an F.R.S-FNRS Research Associate. X.B., S.C., D.G., M.F. and J.L. acknowledge their role as ESA-appointed CHEOPS science team members. Y.A. and M.J.H. acknowledge the support of the Swiss National Fund under grant 200020\_172746. L.Bo., V.Na., I.Pa., G.Pi., R.Ra. and G.Sc. acknowledge support from CHEOPS ASI-INAF agreement n. 2019-29-HH.0. NCS acknowledges support from the European Research Council through the grant agreement 101052347 (FIERCE). This work was supported by FCT – Funda{\c c}{\~a}o para a Ci{\^e}ncia e a Tecnologia through national funds and by FEDER through COMPETE2020 – Programa Operacional Competitividade e Internacionaliza{\c c}{\~a}o by these grants: UIDB/04434/2020; UIDP/04434/2020. A.T. thanks the Science and Technology Facilities Council (STFC) for a PhD studentship. P.E.C. is funded by the Austrian Science Fund (FWF) Erwin Schroedinger Fellowship, program J4595-N.",

year = "2023",

month = jun,

day = "8",

doi = "10.1051/0004-6361/202345943",

language = "English",

volume = "674",

journal = "Astronomy \& Astrophysics",

issn = "0004-6361",

publisher = "EDP Sciences",

}

Garai, Z, Osborn, HP, Gandolfi, D, Brandeker, A, Sousa, SG, Lendl, M, Bekkelien, A, Broeg, C, Cameron, AC, Egger, JA, Hooton, MJ, Alibert, Y, Delrez, L, Fossati, L, Salmon, S, Wilson, TG, Bonfanti, A, Tuson, A, Ulmer-Moll, S, Serrano, LM, Borsato, L, Alonso, R, Anglada, G, Asquier, J, Navascues, DBY, Barros, SCC, Bárczy, T, Baumjohann, W, Beck, M, Beck, T, Benz, W, Billot, N, Biondi, F, Bonfils, X, Buder, M, Cabrera, J, Cessa, V, Charnoz, S, Csizmadia, S, Cubillos, PE, Davies, MB, Deleuil, M, Demangeon, ODS, Demory, B-O, Ehrenreich, D, Erikson, A, Eylen, VV, Fortier, A, Fridlund, M, Gillon, M, Grootel, VV, Güdel, M, Günther, MN, Hoyer, S, Isaak, KG, Kiss, LL, Kristiansen, MH, Laskar, J, Etangs, ALD, Lovis, C, Luntzer, A, Magrin, D, Maxted, PFL, Mordasini, C, Nascimbeni, V, Olofsson, G, Ottensamer, R, Pagano, I, Pallé, E, Peter, G, Piotto, G, Pollacco, D, Queloz, D, Ragazzoni, R, Rando, N, Rauer, H, Ribas, I, Santos, NC, Scandariato, G, Ségransan, D, Simon, AE, Smith, AMS, Steller, M, Szabó, GM, Thomas, N, Udry, S, Venturini, J & Walton, N 2023, 'Refined parameters of the HD 22946 planetary system and the true orbital period of planet d', Astronomy & Astrophysics, vol. 674, A44. https://doi.org/10.1051/0004-6361/202345943

TY - JOUR

T1 - Refined parameters of the HD 22946 planetary system and the true orbital period of planet d

AU - Garai, Z.

AU - Osborn, H. P.

AU - Gandolfi, D.

AU - Brandeker, A.

AU - Sousa, S. G.

AU - Lendl, M.

AU - Bekkelien, A.

AU - Broeg, C.

AU - Cameron, A. Collier

AU - Egger, J. A.

AU - Hooton, M. J.

AU - Alibert, Y.

AU - Delrez, L.

AU - Fossati, L.

AU - Salmon, S.

AU - Wilson, T. G.

AU - Bonfanti, A.

AU - Tuson, A.

AU - Ulmer-Moll, S.

AU - Serrano, L. M.

AU - Borsato, L.

AU - Alonso, R.

AU - Anglada, G.

AU - Asquier, J.

AU - Navascues, D. Barrado y

AU - Barros, S. C. C.

AU - Bárczy, T.

AU - Baumjohann, W.

AU - Beck, M.

AU - Beck, T.

AU - Benz, W.

AU - Billot, N.

AU - Biondi, F.

AU - Bonfils, X.

AU - Buder, M.

AU - Cabrera, J.

AU - Cessa, V.

AU - Charnoz, S.

AU - Csizmadia, Sz.

AU - Cubillos, P. E.

AU - Davies, M. B.

AU - Deleuil, M.

AU - Demangeon, O. D. S.

AU - Demory, B.-O.

AU - Ehrenreich, D.

AU - Erikson, A.

AU - Eylen, V. Van

AU - Fortier, A.

AU - Fridlund, M.

AU - Gillon, M.

AU - Grootel, V. Van

AU - Güdel, M.

AU - Günther, M. N.

AU - Hoyer, S.

AU - Isaak, K. G.

AU - Kiss, L. L.

AU - Kristiansen, M. H.

AU - Laskar, J.

AU - Etangs, A. Lecavelier des

AU - Lovis, C.

AU - Luntzer, A.

AU - Magrin, D.

AU - Maxted, P. F. L.

AU - Mordasini, C.

AU - Nascimbeni, V.

AU - Olofsson, G.

AU - Ottensamer, R.

AU - Pagano, I.

AU - Pallé, E.

AU - Peter, G.

AU - Piotto, G.

AU - Pollacco, D.

AU - Queloz, D.

AU - Ragazzoni, R.

AU - Rando, N.

AU - Rauer, H.

AU - Ribas, I.

AU - Santos, N. C.

AU - Scandariato, G.

AU - Ségransan, D.

AU - Simon, A. E.

AU - Smith, A. M. S.

AU - Steller, M.

AU - Szabó, Gy. M.

AU - Thomas, N.

AU - Udry, S.

AU - Venturini, J.

AU - Walton, N.

N1 - Funding: Z.G. acknowledges the support of the Hungarian National Research, Development and Innovation Office (NKFIH) grant K-125015, the PRODEX Experiment Agreement No. 4000137122 between the ELTE Eötvös Loránd University and the European Space Agency (ESA-D/SCI-LE-2021-0025), the VEGA grant of the Slovak Academy of Sciences No. 2/0031/22, the Slovak Research and Development Agency contract No. APVV-20-0148, and the support of the city of Szombathely. Gy.M.Sz. acknowledges the support of the Hungarian National Research, Development and Innovation Office (NKFIH) grant K-125015, a PRODEX Institute Agreement between the ELTE Eötvös Loránd University and the European Space Agency (ESA-D/SCI-LE-2021-0025), the Lendület LP2018-7/2021 grant of the Hungarian Academy of Science and the support of the city of Szombathely. A.Br. was supported by the SNSA. A.C.C. acknowledges support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1. B.-O.D. acknowledges support from the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number MB22.00046. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (project FOUR ACES; grant agreement No 724427). It has also been carried out in the frame of the National Centre for Competence in Research PlanetS supported by the Swiss National Science Foundation (SNSF). D.E. acknowledges financial support from the Swiss National Science Foundation for project 200021_200726. D.G. gratefully acknowledges financial support from the CRT foundation under Grant No. 2018.2323 “Gaseousor rocky? Unveiling the nature of small worlds”. This work was also partially supported by a grant from the Simons Foundation (PI Queloz, grant number 327127). This work has been carried out within the framework of the NCCR PlanetS supported by the Swiss National Science Foundation under grants 51NF40_182901 and 51NF40_205606. I.R.I. acknowledges support from the Spanish Ministry of Science and Innovation and the European Regional Development Fund through grant PGC2018-098153-B-C33, as well as the support of the Generalitat de Catalunya/CERCA programme. L.D. is an F.R.S.-FNRS Postdoctoral Researcher. L.M.S. gratefully acknowledges financial support from the CRT foundation under Grant No. 2018.2323 “Gaseous or rocky? Unveiling the nature of small worlds”. This project was supported by the CNES. M.F. and C.M.P. gratefully acknowledge the support of the Swedish National Space Agency (DNR 65/19, 174/18). M.G. is an F.R.S.-FNRS Senior Research Associate. M.L. acknowledges support of the Swiss National Science Foundation under grant number PCEFP2_194576. N.A.W. acknowledges UKSA grant ST/R004838/1. This work was supported by FCT – Fundação para a Ciência e a Tecnologia through national funds and by FEDER through COMPETE2020 – Programa Operacional Competitividade e Internacionalizacão by these grants: UID/FIS/04434/2019, UIDB/04434/2020, UIDP/04434/2020, PTDC/FIS-AST/32113/2017 & POCI-01-0145-FEDER-032113, PTDC/FIS-AST/28953/2017 & POCI-01-0145-FEDER-028953, PTDC/FIS-AST/28987/2017 & POCI-01-0145-FEDER-028987, O.D.S.D. is supported in the form of work contract (DL 57/2016/CP1364/CT0004) funded by national funds through FCT. P.M. acknowledges support from STFC research grant number ST/M001040/1. We acknowledge support from 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, PGC2018-098153-B-C33, PGC2018-098153-B-C31, ESP2017-87676-C5-1-R, MDM-2017-0737 Unidad de Excelencia Maria de Maeztu-Centro de Astrobiología (INTA-CSIC), as well as the support of the Generalitat de Catalunya/CERCA programme. The MOC activities have been supported by the ESA contract No. 4000124370. S.H. gratefully acknowledges CNES funding through the grant 837319. S.C.C.B. acknowledges support from FCT through FCT contracts nr. IF/01312/2014/CP1215/CT0004. S.G.S. acknowledges support from FCT through FCT contract no. CEECIND/00826/2018 and POPH/FSE (EC). A.C.C. and T.W. acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1. V.V.G. is an F.R.S-FNRS Research Associate. X.B., S.C., D.G., M.F. and J.L. acknowledge their role as ESA-appointed CHEOPS science team members. Y.A. and M.J.H. acknowledge the support of the Swiss National Fund under grant 200020_172746. L.Bo., V.Na., I.Pa., G.Pi., R.Ra. and G.Sc. acknowledge support from CHEOPS ASI-INAF agreement n. 2019-29-HH.0. NCS acknowledges support from the European Research Council through the grant agreement 101052347 (FIERCE). This work was supported by FCT – Fundação para a Ciência e a Tecnologia through national funds and by FEDER through COMPETE2020 – Programa Operacional Competitividade e Internacionalização by these grants: UIDB/04434/2020; UIDP/04434/2020. A.T. thanks the Science and Technology Facilities Council (STFC) for a PhD studentship. P.E.C. is funded by the Austrian Science Fund (FWF) Erwin Schroedinger Fellowship, program J4595-N.

PY - 2023/6/8

Y1 - 2023/6/8

N2 - Context. Multi-planet systems are important sources of information regarding the evolution of planets. However, the long-period planets in these systems often escape detection. These objects in particular may retain more of their primordial characteristics compared to close-in counterparts because of their increased distance from the host star. HD 22946 is a bright (G = 8.13 mag) late F-type star around which three transiting planets were identified via Transiting Exoplanet Survey Satellite (TESS) photometry, but the true orbital period of the outermost planet d was unknown until now. Aims. We aim to use the Characterising Exoplanet Satellite (CHEOPS) space telescope to uncover the true orbital period of HD 22946d and to refine the orbital and planetary properties of the system, especially the radii of the planets. Methods. We used the available TESS photometry of HD 22946 and observed several transits of the planets b, c, and d using CHEOPS. We identified two transits of planet d in the TESS photometry, calculated the most probable period aliases based on these data, and then scheduled CHEOPS observations. The photometric data were supplemented with ESPRESSO (Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations) radial velocity data. Finally, a combined model was fitted to the entire dataset in order to obtain final planetary and system parameters. Results. Based on the combined TESS and CHEOPS observations, we successfully determined the true orbital period of the planet d to be 47.42489 ± 0.00011 days, and derived precise radii of the planets in the system, namely 1.362 ± 0.040 R⊕, 2.328 ± 0.039 R⊕, and 2.607 ± 0.060 R⊕ for planets b, c, and d, respectively. Due to the low number of radial velocities, we were only able to determine 3σ upper limits for these respective planet masses, which are 13.71 M⊕, 9.72 M⊕, and 26.57 M⊕. We estimated that another 48 ESPRESSO radial velocities are needed to measure the predicted masses of all planets in HD 22946. We also derived stellar parameters for the host star. Conclusions. Planet c around HD 22946 appears to be a promising target for future atmospheric characterisation via transmission spectroscopy. We can also conclude that planet d, as a warm sub-Neptune, is very interesting because there are only a few similar confirmed exoplanets to date. Such objects are worth investigating in the near future, for example in terms of their composition and internal structure.

AB - Context. Multi-planet systems are important sources of information regarding the evolution of planets. However, the long-period planets in these systems often escape detection. These objects in particular may retain more of their primordial characteristics compared to close-in counterparts because of their increased distance from the host star. HD 22946 is a bright (G = 8.13 mag) late F-type star around which three transiting planets were identified via Transiting Exoplanet Survey Satellite (TESS) photometry, but the true orbital period of the outermost planet d was unknown until now. Aims. We aim to use the Characterising Exoplanet Satellite (CHEOPS) space telescope to uncover the true orbital period of HD 22946d and to refine the orbital and planetary properties of the system, especially the radii of the planets. Methods. We used the available TESS photometry of HD 22946 and observed several transits of the planets b, c, and d using CHEOPS. We identified two transits of planet d in the TESS photometry, calculated the most probable period aliases based on these data, and then scheduled CHEOPS observations. The photometric data were supplemented with ESPRESSO (Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations) radial velocity data. Finally, a combined model was fitted to the entire dataset in order to obtain final planetary and system parameters. Results. Based on the combined TESS and CHEOPS observations, we successfully determined the true orbital period of the planet d to be 47.42489 ± 0.00011 days, and derived precise radii of the planets in the system, namely 1.362 ± 0.040 R⊕, 2.328 ± 0.039 R⊕, and 2.607 ± 0.060 R⊕ for planets b, c, and d, respectively. Due to the low number of radial velocities, we were only able to determine 3σ upper limits for these respective planet masses, which are 13.71 M⊕, 9.72 M⊕, and 26.57 M⊕. We estimated that another 48 ESPRESSO radial velocities are needed to measure the predicted masses of all planets in HD 22946. We also derived stellar parameters for the host star. Conclusions. Planet c around HD 22946 appears to be a promising target for future atmospheric characterisation via transmission spectroscopy. We can also conclude that planet d, as a warm sub-Neptune, is very interesting because there are only a few similar confirmed exoplanets to date. Such objects are worth investigating in the near future, for example in terms of their composition and internal structure.

KW - Methods: observational

KW - Techniques: photometric

KW - Planets and satellites: fundamental parameters

U2 - 10.1051/0004-6361/202345943

DO - 10.1051/0004-6361/202345943

M3 - Article

SN - 0004-6361

VL - 674

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

M1 - A44

ER -

Refined parameters of the HD 22946 planetary system and the true orbital period of planet d

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Astronomy at St Andrews 2018-2021: Astronomy at St Andrews 2018-2021

Support for the PLATO Development: Support for the PLATO Development Phase 2017-2022: Planet candidate ranking and validation

Datasets

TESS, CHEOPS and ESPRESSO data of HD 22946 : J/A+A/674/A44

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