TOI-1055 b: Neptunian planet characterised with HARPS, TESS, and CHEOPS

• Published in: Astronomy and astrophysics (Berlin) Vol. 671; p. L8
• Main Authors: Bonfanti, A., Gandolfi, D., Egger, J. A., Fossati, L., Cabrera, J., Krenn, A., Alibert, Y., Benz, W., Billot, N., Florén, H.-G., Lendl, M., Adibekyan, V., Salmon, S., Santos, N. C., Sousa, S. G., Wilson, T. G., Barragán, O., Collier Cameron, A., Delrez, L., Esposito, M., Goffo, E., Osborne, H., Osborn, H. P., Serrano, L. M., Van Eylen, V., Alarcon, J., Alonso, R., Anglada, G., Bárczy, T., Barrado Navascues, D., Barros, S. C. C., Baumjohann, W., Beck, M., Beck, T., Bedell, M., Bonfils, X., Borsato, L., Brandeker, A., Broeg, C., Charnoz, S., Corral Van Damme, C., Csizmadia, Sz, Cubillos, P. E., Davies, M. B., Deleuil, M., Demangeon, O. D. S., Demory, B.-O., Ehrenreich, D., Erikson, A., Fortier, A., Fridlund, M., Gillon, M., Güdel, M., Hoyer, S., Isaak, K. G., Kerschbaum, F., Kiss, L. L., Laskar, J., Lecavelier des Etangs, A., Lorenzo-Oliveira, D., Lovis, C., Magrin, D., Marafatto, L., Maxted, P. F. L., Meléndez, J., Mordasini, C., Nascimbeni, V., Olofsson, G., Ottensamer, R., Pagano, I., Pallé, E., Peter, G., Piazza, D., Piotto, G., Pollacco, D., Queloz, D., Ragazzoni, R., Rando, N., Rauer, H., Ribas, I., Scandariato, G., Ségransan, D., Simon, A. E., Smith, A. M. S., Steller, M., Szabó, Gy. M., Thomas, N., Udry, S., Ulmer, B., Van Grootel, V., Venturini, J., Walton, N. A.
• Format: Journal Article Web Resource
• Language: English
• Published: EDP Sciences 2023
• Subjects: Astronomi, astrofysik och kosmologi; Astronomy, Astrophysics and Cosmology; Astrophysics - Earth and Planetary Astrophysics; Aérospatiale, astronomie & astrophysique; Fysik; Interplanetary flight; Markov processes; Measurements of; Monte Carlo methods; Natural Sciences; Naturvetenskap; Orbits; Photometry; Physical Sciences; Physical, chemical, mathematical & earth Sciences; Physique, chimie, mathématiques & sciences de la terre; Planetary mass; Planets; planets and; Planets and satellites: fundamental parameters; Radial velocity; Satellites; satellites: fundamental parameters; Sciences of the Universe; Space science, astronomy & astrophysics; Spectra's; Stars; Stars: fundamental parameters; Techniques: photometric; Techniques: radial velocities; Time series; Time series analysis; Times series; Velocity analysis; stars: fundamental parameters; techniques: radial velocities; techniques: photometric; Astrophysics - Earth and Planetary Astrophysics; planets and satellites: fundamental parameters
• ISSN: 0004-6361; 1432-0746; 1432-0746; 1432-0756
• DOI: 10.1051/0004-6361/202245607

Context. TOI-1055 is a Sun-like star known to host a transiting Neptune-sized planet on a 17.5-day orbit (TOI-1055 b). Radial velocity (RV) analyses carried out by two independent groups using nearly the same set of HARPS spectra have provided measurements of planetary masses that differ by ∼2 σ . Aims. Our aim in this work is to solve the inconsistency in the published planetary masses by significantly extending the set of HARPS RV measurements and employing a new analysis tool that is able to account and correct for stellar activity. Our further aim was to improve the precision on measurements of the planetary radius by observing two transits of the planet with the CHEOPS space telescope. Methods. We fit a skew normal function to each cross correlation function extracted from the HARPS spectra to obtain RV measurements and hyperparameters to be used for the detrending. We evaluated the correlation changes of the hyperparameters along the RV time series using the breakpoint technique. We performed a joint photometric and RV analysis using a Markov chain Monte Carlo scheme to simultaneously detrend the light curves and the RV time series. Results. We firmly detected the Keplerian signal of TOI-1055 b, deriving a planetary mass of M b  = 20.4 −2.5 +2.6   M ⊕ (∼12%). This value is in agreement with one of the two estimates in the literature, but it is significantly more precise. Thanks to the TESS transit light curves combined with exquisite CHEOPS photometry, we also derived a planetary radius of R b  = 3.490 −0.064 +0.070   R ⊕ (∼1.9%). Our mass and radius measurements imply a mean density of ρ b  = 2.65 −0.35 +0.37 g cm −3 (∼14%). We further inferred the planetary structure and found that TOI-1055 b is very likely to host a substantial gas envelope with a mass of 0.41 −0.20 +0.34   M ⊕ and a thickness of 1.05 −0.29 +0.30   R ⊕ . Conclusions. Our RV extraction combined with the breakpoint technique has played a key role in the optimal removal of stellar activity from the HARPS time series, enabling us to solve the tension in the planetary mass values published so far for TOI-1055 b.