HARPS-N, TESS, and CHEOPS discover a transiting sub-Neptune and two outer companions around the bright solar analogue HD 85426

F Lienhard; A Mortier; A Collier Cameron; M Cretignier; L Borsato; A Anna John; J A Egger; M Stalport; T G Wilson; A Deline; A Fortier; D W Latham; L Malavolta; P F L Maxted; S G Sousa; S L Grimm; L Buchhave; Y Alibert; B S Lakeland; X Dumusque; J Cabrera; L Naponiello; A C M Correia; F Rescigno; L Fossati; A Sozzetti; R Alonso; T Bárczy; D Barrado; S C C Barros; W Baumjohann; W Benz; N Billot; A Brandeker; C Broeg; K Collins; Sz Csizmadia; P E Cubillos; M B Davies; M Deleuil; O D S Demangeon; B -O Demory; A Derekas; B Edwards; D Ehrenreich; A Erikson; M Fridlund; D Gandolfi; K Gazeas; M Gillon; M Güdel; M N Günther; R Haywood; A Heitzmann; Ch Helling; K G Isaak; J M Jenkins; L L Kiss; J Korth; K W F Lam; J Laskar; A Lecavelier des Etangs; A Leleu; M Lendl; D Magrin; A F Martínez Fiorenzano; B Merín; C Mordasini; V Nascimbeni; G Olofsson; H P Osborn; R Ottensamer; I Pagano; L Palethorpe; E Pallé; G Peter; D Piazza; G Piotto; D Pollacco; D Queloz; R Ragazzoni; N Rando; H Rauer; I Ribas; K Rice; N C Santos; G Scandariato; D Ségransan; A E Simon; A M S Smith; S Sulis; Gy M Szabó; S Udry; S Ulmer-Moll; V Van Grootel; J Venturini; E Villaver; N A Walton; T Zingales

doi:10.1093/mnras/staf1934

HARPS-N, TESS, and CHEOPS discover a transiting sub-Neptune and two outer companions around the bright solar analogue HD 85426

F Lienhard^*, A Mortier, A Collier Cameron, M Cretignier, L Borsato, A Anna John, J A Egger, M Stalport, T G Wilson, A Deline, A Fortier, D W Latham, L Malavolta, P F L Maxted, S G Sousa, S L Grimm, L Buchhave, Y Alibert, B S Lakeland, X DumusqueJ Cabrera, L Naponiello, A C M Correia, F Rescigno, L Fossati, A Sozzetti, R Alonso, T Bárczy, D Barrado, S C C Barros, W Baumjohann, W Benz, N Billot, A Brandeker, C Broeg, K Collins, Sz Csizmadia, P E Cubillos, M B Davies, M Deleuil, O D S Demangeon, B -O Demory, A Derekas, B Edwards, D Ehrenreich, A Erikson, M Fridlund, D Gandolfi, K Gazeas, M Gillon, M Güdel, M N Günther, R Haywood, A Heitzmann, Ch Helling, K G Isaak, J M Jenkins, L L Kiss, J Korth, K W F Lam, J Laskar, A Lecavelier des Etangs, A Leleu, M Lendl, D Magrin, A F Martínez Fiorenzano, B Merín, C Mordasini, V Nascimbeni, G Olofsson, H P Osborn, R Ottensamer, I Pagano, L Palethorpe, E Pallé, G Peter, D Piazza, G Piotto, D Pollacco, D Queloz, R Ragazzoni, N Rando, H Rauer, I Ribas, K Rice, N C Santos, G Scandariato, D Ségransan, A E Simon, A M S Smith, S Sulis, Gy M Szabó, S Udry, S Ulmer-Moll, V Van Grootel, J Venturini, E Villaver, N A Walton, T Zingales

^*Corresponding author for this work

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

Abstract

We provide a detailed characterization of the planetary system orbiting HD 85426 (TOI-1774). This bright G-type star (M_∗: 0.99 M_☉; R_∗: 1.13 R_☉; age: 7.4 Gyr; V mag: 8.25) hosts a transiting sub-Neptune, HD 85426 b, with an orbital period of 16.71 d and a blackbody equilibrium temperature of 824₋₁₁⁺¹¹ K. By jointly analysing HARPS-N RVs, TESS, and CHEOPS photometric data and using two different stellar activity mitigation techniques, we constrain planet b’s mass to 6.0_−1.6^+1.5 M_⊕ and 8.5_−1.4^+1.3 M_⊕, depending on the mitigation technique. We investigate the dependence of these results on the priors, data selection, and inclusion of other Keplerians in the modelling. Using this approach, we identify the presence of two non-transiting planetary companions with minimum masses near 10 M_⊕ and orbital periods of 35.7 and 89 d. Additionally, we reject the initial hypothesis that the 35.7-d periodic signal was due to stellar activity. We also determine HD 85426 b’s radius to be 2.78_−0.04^+0.05 R_⊕ and compute a transmission spectroscopy metric in the range of 82 to 115, making this planet a highly valuable target for atmospheric characterization.

Original language	English
Article number	staf1934
Number of pages	26
Journal	Monthly Notices of the Royal Astronomical Society
Volume	545
Issue number	3
DOIs	https://doi.org/10.1093/mnras/staf1934
Publication status	Published - 2 Jan 2026

Keywords

Techniques: photometric
Techniques: radial velocities
Techniques: spectroscopic
Planets and satellites: composition
Planets and satellites: fundamental parameters
Stars: individual (HD 85426)

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Lienhard_2026_MNRAS_HARPS-N-transiting-sub-Neptune-HD-85426_CC
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1 Active

REVEAL: REVEALing Signatures of Habitable Worlds Hidden by Stellar Activity
Cameron, A. (PI)
UKRI (EU)
1/08/24 → 31/07/30
Project: Standard
H2020 MSCA ITN EJD 2019: H2020 MSCA ITN EJD 2019 CHAMELEON
Helling, C. (PI)
Joint Research Centre European Commission
1/06/20 → 31/05/24
Project: Standard

Cite this

Lienhard, F., Mortier, A., Cameron, A. C., Cretignier, M., Borsato, L., John, A. A., Egger, J. A., Stalport, M., Wilson, T. G., Deline, A., Fortier, A., Latham, D. W., Malavolta, L., Maxted, P. F. L., Sousa, S. G., Grimm, S. L., Buchhave, L., Alibert, Y., Lakeland, B. S., ... Zingales, T. (2026). HARPS-N, TESS, and CHEOPS discover a transiting sub-Neptune and two outer companions around the bright solar analogue HD 85426. Monthly Notices of the Royal Astronomical Society, 545(3), Article staf1934. https://doi.org/10.1093/mnras/staf1934

@article{769d3508dc8d48429a004b27c18595d1,

title = "HARPS-N, TESS, and CHEOPS discover a transiting sub-Neptune and two outer companions around the bright solar analogue HD 85426",

abstract = "We provide a detailed characterization of the planetary system orbiting HD 85426 (TOI-1774). This bright G-type star (M∗: 0.99 M☉; R∗: 1.13 R☉; age: 7.4 Gyr; V mag: 8.25) hosts a transiting sub-Neptune, HD 85426 b, with an orbital period of 16.71 d and a blackbody equilibrium temperature of 824−11+11 K. By jointly analysing HARPS-N RVs, TESS, and CHEOPS photometric data and using two different stellar activity mitigation techniques, we constrain planet b{\textquoteright}s mass to 6.0−1.6+1.5 M⊕ and 8.5−1.4+1.3 M⊕, depending on the mitigation technique. We investigate the dependence of these results on the priors, data selection, and inclusion of other Keplerians in the modelling. Using this approach, we identify the presence of two non-transiting planetary companions with minimum masses near 10 M⊕ and orbital periods of 35.7 and 89 d. Additionally, we reject the initial hypothesis that the 35.7-d periodic signal was due to stellar activity. We also determine HD 85426 b{\textquoteright}s radius to be 2.78−0.04+0.05 R⊕ and compute a transmission spectroscopy metric in the range of 82 to 115, making this planet a highly valuable target for atmospheric characterization.",

keywords = "Techniques: photometric, Techniques: radial velocities, Techniques: spectroscopic, Planets and satellites: composition, Planets and satellites: fundamental parameters, Stars: individual (HD 85426)",

author = "F Lienhard and A Mortier and Cameron, \{A Collier\} and M Cretignier and L Borsato and John, \{A Anna\} and Egger, \{J A\} and M Stalport and Wilson, \{T G\} and A Deline and A Fortier and Latham, \{D W\} and L Malavolta and Maxted, \{P F L\} and Sousa, \{S G\} and Grimm, \{S L\} and L Buchhave and Y Alibert and Lakeland, \{B S\} and X Dumusque and J Cabrera and L Naponiello and Correia, \{A C M\} and F Rescigno and L Fossati and A Sozzetti and R Alonso and T B{\'a}rczy and D Barrado and Barros, \{S C C\} and W Baumjohann and W Benz and N Billot and A Brandeker and C Broeg and K Collins and Sz Csizmadia and Cubillos, \{P E\} and Davies, \{M B\} and M Deleuil and Demangeon, \{O D S\} and Demory, \{B -O\} and A Derekas and B Edwards and D Ehrenreich and A Erikson and M Fridlund and D Gandolfi and K Gazeas and M Gillon and M G{\"u}del and G{\"u}nther, \{M N\} and R Haywood and A Heitzmann and Ch Helling and Isaak, \{K G\} and Jenkins, \{J M\} and Kiss, \{L L\} and J Korth and Lam, \{K W F\} and J Laskar and Etangs, \{A Lecavelier des\} and A Leleu and M Lendl and D Magrin and Fiorenzano, \{A F Mart{\'i}nez\} and B Mer{\'i}n and C Mordasini and V Nascimbeni and G Olofsson and Osborn, \{H P\} and R Ottensamer and I Pagano and L Palethorpe and E Pall{\'e} and G Peter and D Piazza and G Piotto and D Pollacco and D Queloz and R Ragazzoni and N Rando and H Rauer and I Ribas and K Rice and Santos, \{N C\} and G Scandariato and D S{\'e}gransan and Simon, \{A E\} and Smith, \{A M S\} and S Sulis and Szab{\'o}, \{Gy M\} and S Udry and S Ulmer-Moll and V Van Grootel and J Venturini and E Villaver and Walton, \{N A\} and T Zingales",

note = "Funding: AM acknowledges funding from a UKRI Future Leader Fellowship, grant number MR/X033244/1 and a UK Science and Technology Facilities Council (STFC) small grant ST/Y002334/1. ACC acknowledges support from STFC consolidated grant number ST/V000861/1and UKRI/ERC Synergy Grant EP/Z000181/1(REVEAL). BSL acknowledges funding from a UKRI Future Leader Fellowship (grant number MR/X033244/1). RDH is funded by the UK Science and Technology Facilities Council (STFC){\textquoteright}s Ernest Rutherford Fellowship (grant number ST/V004735/1). LBo, GBr, VNa, IPa, GPi, RRa, GSc, VSi, and TZi acknowledge support from CHEOPS ASI-INAF agreement n. 2019-29-HH.0. LBo acknowledges financial support from the Bando Ricerca Fondamentale INAF 2023, Mini-Grant: {\textquoteleft}Decoding the dynamical properties of planetary systems observed by TESS and CHEOPS through TTV analysis with parallel computing{\textquoteright}. TZi acknowledges support from NVIDIA Academic Hardware Grant Program for the use of the Titan V GPU card and the Italian MUR Departments of Excellence grant 2023–2027 {\textquoteleft}Quantum Frontiers{\textquoteright}. 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. TWi acknowledges support from the UKSA and the University of Warwick. PM acknowledges support from STFC research grant number ST/R000638/1. SGS acknowledge support from FCT through FCT contract nr. CEECIND/00826/2018 and POPH/FSE (EC). The Portuguese team thanks the Portuguese Space Agency for the provision of financial support in the framework of the PRODEX Programme of the European Space Agency (ESA) under contract number 4000142255. YAl acknowledges support from the Swiss National Science Foundation (SNSF) under grant 200020\_192038. ACMC acknowledges support from the FCT, Portugal, through the CFisUC projects UIDB/04564/2020 and UIDP/04564/2020, with DOI identifiers 10.54499/UIDB/04564/2020 and 10.54499/UIDP/04564/2020, respectively. DB, EP, EV, IR, and RA acknowledge financial support from the Agencia Estatal de Investigaci{\'o}n of the Ministerio de Ciencia e Innovaci{\'o}n MCIN/AEI/10.13039/501100011033 and the ERDF {\textquoteleft}A way of making Europe{\textquoteright} through projects PID2021-125627OB-C31, PID2021-125627OB-C32, PID2021-127289NB-I00, PID2023-150468NB-I00 and PID2023-149439NB-C41. from the Centre of Excellence {\textquoteleft}Severo Ochoa{\textquoteright} award to the Instituto de Astrof{\'i}sica de Canarias (CEX2019-000920-S), the Centre of Excellence {\textquoteleft}Mar{\'i}a de Maeztu{\textquoteright} award to the Institut de Ci{\`e}ncies de l{\textquoteright}Espai (CEX2020-001058-M), and from the Generalitat de Catalunya/CERCA programme. SCCB acknowledges the support from Funda{\c c}{\~a}o para a Ci{\^e}ncia e Tecnologia (FCT) in the form of work contract through the Scientific Employment Incentive program with reference 2023.06687.CEECIND and DOI 10.54499/2023.06687.CEECIND/CP2839/CT0002. ABr was supported by the SNSA. CB and AS acknowledge support from the Swiss Space Office through the ESA PRODEX program. P.E.C. is funded by the Austrian Science Fund (FWF) Erwin Schroedinger Fellowship, programme J4595-N. This project was supported by the CNES. 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 through the research grants UIDB/04434/2020, UIDP/04434/2020, 2022.06962.PTDC. O.D.S.D. is supported in the form of work contract (DL 57/2016/CP1364/CT0004) funded by national funds through FCT. B-OD 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 Swiss National Science Foundation for project 200021\_200726. It has also been carried out within the framework of the National Centre of Competence in Research PlanetS supported by the Swiss National Science Foundation under grant 51NF40\_205606. The authors acknowledge the financial support of the SNSF. MF and CMP gratefully acknowledge the support of the Swedish National Space Agency (DNR 65/19, 174/18). DG gratefully acknowledges financial support from the CRT foundation under Grant No. 2018.2323 {\textquoteleft}Gaseous or rocky? Unveiling the nature of small worlds{\textquoteright}. CHe acknowledges financial support from the {\"O}sterreichische Akademie 1158 der Wissenschaften and from the European Union H2020-MSCA-ITN-2019 1159 under Grant Agreement no. 860470 (CHAMELEON). AL and JK acknowledge support of the Swiss National Science Foundation under grant number TMSGI2\_211697. ML acknowledges support of the Swiss National Science Foundation under grant number PCEFP2\_194576. This work was also partially supported by a grant from the Simons Foundation (PI Queloz, grant number 327127). NCSa acknowledges funding by the European Union (ERC, FIERCE, 101052347). GyMSz acknowledges the support of the Hungarian National Research, Development and Innovation Office (NKFIH) grant K-125015, a PRODEX Experiment Agreement No. 4000137122, the Lend{\"u}let LP2018-7/2021 grant of the Hungarian Academy of Science and the support of the city of Szombathely. VVG is an F.R.S-FNRS Research Associate. JV acknowledges support from the Swiss National Science Foundation (SNSF) under grant PZ00P2\_208945. NAW acknowledges UKSA grant ST/R004838/1.",

year = "2026",

month = jan,

day = "2",

doi = "10.1093/mnras/staf1934",

language = "English",

volume = "545",

journal = "Monthly Notices of the Royal Astronomical Society",

issn = "0035-8711",

publisher = "Oxford University Press",

number = "3",

}

Lienhard, F, Mortier, A, Cameron, AC, Cretignier, M, Borsato, L, John, AA, Egger, JA, Stalport, M, Wilson, TG, Deline, A, Fortier, A, Latham, DW, Malavolta, L, Maxted, PFL, Sousa, SG, Grimm, SL, Buchhave, L, Alibert, Y, Lakeland, BS, Dumusque, X, Cabrera, J, Naponiello, L, Correia, ACM, Rescigno, F, Fossati, L, Sozzetti, A, Alonso, R, Bárczy, T, Barrado, D, Barros, SCC, Baumjohann, W, Benz, W, Billot, N, Brandeker, A, Broeg, C, Collins, K, Csizmadia, S, Cubillos, PE, Davies, MB, Deleuil, M, Demangeon, ODS, Demory, B-O, Derekas, A, Edwards, B, Ehrenreich, D, Erikson, A, Fridlund, M, Gandolfi, D, Gazeas, K, Gillon, M, Güdel, M, Günther, MN, Haywood, R, Heitzmann, A, Helling, C, Isaak, KG, Jenkins, JM, Kiss, LL, Korth, J, Lam, KWF, Laskar, J, Etangs, ALD, Leleu, A, Lendl, M, Magrin, D, Fiorenzano, AFM, Merín, B, Mordasini, C, Nascimbeni, V, Olofsson, G, Osborn, HP, Ottensamer, R, Pagano, I, Palethorpe, L, Pallé, E, Peter, G, Piazza, D, Piotto, G, Pollacco, D, Queloz, D, Ragazzoni, R, Rando, N, Rauer, H, Ribas, I, Rice, K, Santos, NC, Scandariato, G, Ségransan, D, Simon, AE, Smith, AMS, Sulis, S, Szabó, GM, Udry, S, Ulmer-Moll, S, Van Grootel, V, Venturini, J, Villaver, E, Walton, NA & Zingales, T 2026, 'HARPS-N, TESS, and CHEOPS discover a transiting sub-Neptune and two outer companions around the bright solar analogue HD 85426', Monthly Notices of the Royal Astronomical Society, vol. 545, no. 3, staf1934. https://doi.org/10.1093/mnras/staf1934

TY - JOUR

T1 - HARPS-N, TESS, and CHEOPS discover a transiting sub-Neptune and two outer companions around the bright solar analogue HD 85426

AU - Lienhard, F

AU - Mortier, A

AU - Cameron, A Collier

AU - Cretignier, M

AU - Borsato, L

AU - John, A Anna

AU - Egger, J A

AU - Stalport, M

AU - Wilson, T G

AU - Deline, A

AU - Fortier, A

AU - Latham, D W

AU - Malavolta, L

AU - Maxted, P F L

AU - Sousa, S G

AU - Grimm, S L

AU - Buchhave, L

AU - Alibert, Y

AU - Lakeland, B S

AU - Dumusque, X

AU - Cabrera, J

AU - Naponiello, L

AU - Correia, A C M

AU - Rescigno, F

AU - Fossati, L

AU - Sozzetti, A

AU - Alonso, R

AU - Bárczy, T

AU - Barrado, D

AU - Barros, S C C

AU - Baumjohann, W

AU - Benz, W

AU - Billot, N

AU - Brandeker, A

AU - Broeg, C

AU - Collins, K

AU - Csizmadia, Sz

AU - Cubillos, P E

AU - Davies, M B

AU - Deleuil, M

AU - Demangeon, O D S

AU - Demory, B -O

AU - Derekas, A

AU - Edwards, B

AU - Ehrenreich, D

AU - Erikson, A

AU - Fridlund, M

AU - Gandolfi, D

AU - Gazeas, K

AU - Gillon, M

AU - Güdel, M

AU - Günther, M N

AU - Haywood, R

AU - Heitzmann, A

AU - Helling, Ch

AU - Isaak, K G

AU - Jenkins, J M

AU - Kiss, L L

AU - Korth, J

AU - Lam, K W F

AU - Laskar, J

AU - Etangs, A Lecavelier des

AU - Leleu, A

AU - Lendl, M

AU - Magrin, D

AU - Fiorenzano, A F Martínez

AU - Merín, B

AU - Mordasini, C

AU - Nascimbeni, V

AU - Olofsson, G

AU - Osborn, H P

AU - Ottensamer, R

AU - Pagano, I

AU - Palethorpe, L

AU - Pallé, E

AU - Peter, G

AU - Piazza, D

AU - Piotto, G

AU - Pollacco, D

AU - Queloz, D

AU - Ragazzoni, R

AU - Rando, N

AU - Rauer, H

AU - Ribas, I

AU - Rice, K

AU - Santos, N C

AU - Scandariato, G

AU - Ségransan, D

AU - Simon, A E

AU - Smith, A M S

AU - Sulis, S

AU - Szabó, Gy M

AU - Udry, S

AU - Ulmer-Moll, S

AU - Van Grootel, V

AU - Venturini, J

AU - Villaver, E

AU - Walton, N A

AU - Zingales, T

N1 - Funding: AM acknowledges funding from a UKRI Future Leader Fellowship, grant number MR/X033244/1 and a UK Science and Technology Facilities Council (STFC) small grant ST/Y002334/1. ACC acknowledges support from STFC consolidated grant number ST/V000861/1and UKRI/ERC Synergy Grant EP/Z000181/1(REVEAL). BSL acknowledges funding from a UKRI Future Leader Fellowship (grant number MR/X033244/1). RDH is funded by the UK Science and Technology Facilities Council (STFC)’s Ernest Rutherford Fellowship (grant number ST/V004735/1). LBo, GBr, VNa, IPa, GPi, RRa, GSc, VSi, and TZi acknowledge support from CHEOPS ASI-INAF agreement n. 2019-29-HH.0. LBo acknowledges financial support from the Bando Ricerca Fondamentale INAF 2023, Mini-Grant: ‘Decoding the dynamical properties of planetary systems observed by TESS and CHEOPS through TTV analysis with parallel computing’. TZi acknowledges support from NVIDIA Academic Hardware Grant Program for the use of the Titan V GPU card and the Italian MUR Departments of Excellence grant 2023–2027 ‘Quantum Frontiers’. 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. TWi acknowledges support from the UKSA and the University of Warwick. PM acknowledges support from STFC research grant number ST/R000638/1. SGS acknowledge support from FCT through FCT contract nr. CEECIND/00826/2018 and POPH/FSE (EC). The Portuguese team thanks the Portuguese Space Agency for the provision of financial support in the framework of the PRODEX Programme of the European Space Agency (ESA) under contract number 4000142255. YAl acknowledges support from the Swiss National Science Foundation (SNSF) under grant 200020_192038. ACMC acknowledges support from the FCT, Portugal, through the CFisUC projects UIDB/04564/2020 and UIDP/04564/2020, with DOI identifiers 10.54499/UIDB/04564/2020 and 10.54499/UIDP/04564/2020, respectively. DB, EP, EV, IR, and RA acknowledge financial support from the Agencia Estatal de Investigación of the Ministerio de Ciencia e Innovación MCIN/AEI/10.13039/501100011033 and the ERDF ‘A way of making Europe’ through projects PID2021-125627OB-C31, PID2021-125627OB-C32, PID2021-127289NB-I00, PID2023-150468NB-I00 and PID2023-149439NB-C41. from the Centre of Excellence ‘Severo Ochoa’ award to the Instituto de Astrofísica de Canarias (CEX2019-000920-S), the Centre of Excellence ‘María de Maeztu’ award to the Institut de Ciències de l’Espai (CEX2020-001058-M), and from the Generalitat de Catalunya/CERCA programme. SCCB acknowledges the support from Fundação para a Ciência e Tecnologia (FCT) in the form of work contract through the Scientific Employment Incentive program with reference 2023.06687.CEECIND and DOI 10.54499/2023.06687.CEECIND/CP2839/CT0002. ABr was supported by the SNSA. CB and AS acknowledge support from the Swiss Space Office through the ESA PRODEX program. P.E.C. is funded by the Austrian Science Fund (FWF) Erwin Schroedinger Fellowship, programme J4595-N. This project was supported by the CNES. This work was supported by FCT—Fundação para a Ciência e a Tecnologia through national funds and by FEDER through COMPETE2020 through the research grants UIDB/04434/2020, UIDP/04434/2020, 2022.06962.PTDC. O.D.S.D. is supported in the form of work contract (DL 57/2016/CP1364/CT0004) funded by national funds through FCT. B-OD 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 Swiss National Science Foundation for project 200021_200726. It has also been carried out within the framework of the National Centre of Competence in Research PlanetS supported by the Swiss National Science Foundation under grant 51NF40_205606. The authors acknowledge the financial support of the SNSF. MF and CMP gratefully acknowledge the support of the Swedish National Space Agency (DNR 65/19, 174/18). DG gratefully acknowledges financial support from the CRT foundation under Grant No. 2018.2323 ‘Gaseous or rocky? Unveiling the nature of small worlds’. CHe acknowledges financial support from the Österreichische Akademie 1158 der Wissenschaften and from the European Union H2020-MSCA-ITN-2019 1159 under Grant Agreement no. 860470 (CHAMELEON). AL and JK acknowledge support of the Swiss National Science Foundation under grant number TMSGI2_211697. ML acknowledges support of the Swiss National Science Foundation under grant number PCEFP2_194576. This work was also partially supported by a grant from the Simons Foundation (PI Queloz, grant number 327127). NCSa acknowledges funding by the European Union (ERC, FIERCE, 101052347). GyMSz acknowledges the support of the Hungarian National Research, Development and Innovation Office (NKFIH) grant K-125015, a PRODEX Experiment Agreement No. 4000137122, the Lendület LP2018-7/2021 grant of the Hungarian Academy of Science and the support of the city of Szombathely. VVG is an F.R.S-FNRS Research Associate. JV acknowledges support from the Swiss National Science Foundation (SNSF) under grant PZ00P2_208945. NAW acknowledges UKSA grant ST/R004838/1.

PY - 2026/1/2

Y1 - 2026/1/2

N2 - We provide a detailed characterization of the planetary system orbiting HD 85426 (TOI-1774). This bright G-type star (M∗: 0.99 M☉; R∗: 1.13 R☉; age: 7.4 Gyr; V mag: 8.25) hosts a transiting sub-Neptune, HD 85426 b, with an orbital period of 16.71 d and a blackbody equilibrium temperature of 824−11+11 K. By jointly analysing HARPS-N RVs, TESS, and CHEOPS photometric data and using two different stellar activity mitigation techniques, we constrain planet b’s mass to 6.0−1.6+1.5 M⊕ and 8.5−1.4+1.3 M⊕, depending on the mitigation technique. We investigate the dependence of these results on the priors, data selection, and inclusion of other Keplerians in the modelling. Using this approach, we identify the presence of two non-transiting planetary companions with minimum masses near 10 M⊕ and orbital periods of 35.7 and 89 d. Additionally, we reject the initial hypothesis that the 35.7-d periodic signal was due to stellar activity. We also determine HD 85426 b’s radius to be 2.78−0.04+0.05 R⊕ and compute a transmission spectroscopy metric in the range of 82 to 115, making this planet a highly valuable target for atmospheric characterization.

AB - We provide a detailed characterization of the planetary system orbiting HD 85426 (TOI-1774). This bright G-type star (M∗: 0.99 M☉; R∗: 1.13 R☉; age: 7.4 Gyr; V mag: 8.25) hosts a transiting sub-Neptune, HD 85426 b, with an orbital period of 16.71 d and a blackbody equilibrium temperature of 824−11+11 K. By jointly analysing HARPS-N RVs, TESS, and CHEOPS photometric data and using two different stellar activity mitigation techniques, we constrain planet b’s mass to 6.0−1.6+1.5 M⊕ and 8.5−1.4+1.3 M⊕, depending on the mitigation technique. We investigate the dependence of these results on the priors, data selection, and inclusion of other Keplerians in the modelling. Using this approach, we identify the presence of two non-transiting planetary companions with minimum masses near 10 M⊕ and orbital periods of 35.7 and 89 d. Additionally, we reject the initial hypothesis that the 35.7-d periodic signal was due to stellar activity. We also determine HD 85426 b’s radius to be 2.78−0.04+0.05 R⊕ and compute a transmission spectroscopy metric in the range of 82 to 115, making this planet a highly valuable target for atmospheric characterization.

KW - Techniques: photometric

KW - Techniques: radial velocities

KW - Techniques: spectroscopic

KW - Planets and satellites: composition

KW - Planets and satellites: fundamental parameters

KW - Stars: individual (HD 85426)

U2 - 10.1093/mnras/staf1934

DO - 10.1093/mnras/staf1934

M3 - Article

SN - 0035-8711

VL - 545

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

IS - 3

M1 - staf1934

ER -

HARPS-N, TESS, and CHEOPS discover a transiting sub-Neptune and two outer companions around the bright solar analogue HD 85426

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REVEAL: REVEALing Signatures of Habitable Worlds Hidden by Stellar Activity

H2020 MSCA ITN EJD 2019: H2020 MSCA ITN EJD 2019 CHAMELEON

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