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

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

aa45943-23.pdf - Published Version
Available under License Creative Commons: Attribution (CC-BY).

Download (1MB) | Preview

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.

Item Type:

Journal Article (Original Article)


08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences > Theoretical Astrophysics and Planetary Science (TAPS)
08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences
08 Faculty of Science > Physics Institute
10 Strategic Research Centers > Center for Space and Habitability (CSH)
08 Faculty of Science > Physics Institute > NCCR PlanetS

UniBE Contributor:

Osborn, Hugh Patrick, Broeg, Christopher, Egger, Jo Ann, Hooton, Matthew John, Alibert, Yann Daniel Pierre, Ulmer-Moll, Solène Chloé, Beck, Thomas, Benz, Willy, Cessa, Virginie, Demory, Brice-Olivier Denys, Fortier, A., Mordasini, Christoph, Simon, Attila, Thomas, Nicolas, Venturini Corbellini, Julia Elisa


500 Science > 520 Astronomy
600 Technology > 620 Engineering
500 Science > 530 Physics
500 Science




EDP Sciences




Danielle Zemp

Date Deposited:

15 Apr 2024 11:13

Last Modified:

15 Apr 2024 11:13

Publisher DOI:





Actions (login required)

Edit item Edit item
Provide Feedback