[Astronomy & Astrophysics] Close-in substellar companions experience strong tidal and magnetic interactions with their host stars and are therefore subject to fast orbital evolution.
Moreover, due to the strong irradiation of their surface, they exhibit orbital phase modulations of significant amplitudes, allowing their atmospheric radiative properties to be characterised.
Close-in substellar companions experience strong tidal and magnetic interactions with their host stars and are therefore subject to fast orbital evolution. — Astronomy & Astrophysics
In particular, this means that companions can be detected and characterised even in the absence of transits. The solar-type pulsator KIC 9139163 exhibits, in its light curve, a stable 0.6-day modulation for which the best explanation is the presence of a close-in non-transiting companion that we therefore attempt to characterise.
We combined Kepler and TESS photometric data with spectroscopic observations obtained with the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N). We validated the KIC 9139163 surface stellar rotation period and we used the HARPS-N spectra to refine the stellar modelling. The analysis of the radial velocities obtained with HARPS-N provides a companion mass Mp ~ i = 7.3 ± 1.4 M⊕.
Using a joint grid fitting of the Kepler and TESS phase curves with an ultra-hot exoplanet model, we inferred a planetary radius of 2.43 ± 0.14 R⊕, which, combined with the measured mass and retrieved inclination, implies a bulk density consistent with a hot water-rich world.
This places the non-transiting companion candidate of KIC 9139163 within the Neptunian desert, a regime where planets are expected either to have lost their primordial hydrogen or helium envelopes or to harbour metal-enriched atmospheres.
We further detected significant variations in amplitude between the Kepler and TESS phase curves, obtained 6 years apart, as well as a secular increase in amplitude over the Kepler baseline. Our joint fit favours a model with two distinct longitudinal cloud offsets over a single-offset scenario. Both datasets indicate a moderate-to-high geometric albedo and low-to-moderate heat redistribution.
The opposite phase offsets observed in the Kepler and TESS datasets suggest a time-variable longitudinal brightness distribution, potentially driven by evolving cloud properties or changes in scattering behaviour.
Nevertheless, given the larger noise level and contamination affecting the TESS photometry, this interpretation remains tentative. These results point towards a dynamic and evolving reflective component in the atmosphere of the candidate planet.
While making KIC 9139163 an interesting candidate for future ground follow-ups, it also suggests that searching for other non-transiting planets around fast stellar rotators in space-borne photometric surveys might provide new insights into the physics of the Neptunian planets located in the desert.
Hidden worlds: A non-transiting candidate planet in the Neptunian desert around the solar-type pulsator KIC 9139163, Astronomy & Astrophysics
Astrobiology, Astronomy, Exoplanet,
