The RoPES project with HARPS and HARPS-N

III. Two candidate planets orbiting the G-type star HD 161098

¹ Light Bridges S.L., Observatorio del Teide, Carretera del Observatorio s/n, Güimar, 38500 Tenerife, Spain
² Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁴ Consejo Superior de Investigaciones Científicas, Spain
⁵ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁶ Observatoire de Genève, Département d’Astronomie, Université de Genève, Chemin Pegasi 51b, 1290 Versoix, Switzerland
⁷ Department of Physics, University of Oxford, Oxford OX1 3RH, UK
⁸ Subaru Telescope, National Astronomical Observatory of Japan, 650 N Aohoku Place, Hilo, HI 96720, USA
⁹ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
¹⁰ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹¹ Dipartimento di Fisica, Università di Roma “Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Rome, Italy
¹² INAF – Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
¹³ Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, Campus Universitário, Natal, Rio Grande do Norte 59072-970, Brazil

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 23 January 2026
Accepted: 9 March 2026

Abstract

Context. The development of refined instruments and techniques for a detailed analysis of the radial velocities (RVs) of stars other than the Sun allows the presence of planetary signals of amplitude below 1 m s⁻¹ to be investigated. Long-term RV surveys allow the detection of Earth-like and super-Earth-like planets in the habitable zones of Sun-like stars, prime targets for future missions for the atmospheric characterization of exoplanets.

Aims. We present the analysis of the nearby G8 V-type star HD 161098 (V = 7.68 mag, d = 29.75 pc). We searched for terrestrial planets in the habitable zone.

Methods. We combined historical datasets with new data collected in an ongoing blind search program with HARPS, HARPS-N, and ESPRESSO. We utilized recently developed tools to extract RVs and to deal with the analysis of stellar activity. We performed a joint analysis of RVs and activity indicators to separate the planetary signals from those related to activity.

Results. We detected two sub-m s⁻¹ signals that we claim as candidate planets. We are not able to confirm their nature with certainty. Candidate HD 161098 b has an orbital period of 72.578_−0.060^+0.059 d and a minimum mass of 3.63 ± 0.59 M_⊕. HD 161098 c has an orbital period of 682.5_−9.9^+9.5 d and a minimum mass of 7.8_−1.4^+1.5 M_⊕. If confirmed, candidate HD 161098 c would reside in the optimistic habitable zone of the star. We find a magnetic cycle of 4090₋₁₃₀⁺¹⁴⁰ d period and a rotation period of 28.22_−0.35^+0.30 d. Our analysis sets the stage for future observing campaigns of the star, finalized for the confirmation of our results.

Conclusions. We are entering the sub-m s⁻¹ era at long orbital periods with a combination of stellar activity treatment and long-term campaigns.