TOI-5005 b: A super-Neptune in the savanna near the ridge
astro-ph.EP
/ Authors
A. Castro-González, J. Lillo-Box, D. J. Armstrong, L. Acuña, A. Aguichine, V. Bourrier, S. Gandhi, S. G. Sousa, E. Delgado-Mena, A. Moya
and 31 more authors
V. Adibekyan, A. C. M. Correia, D. Barrado, M. Damasso, J. N. Winn, N. C. Santos, K. Barkaoui, S. C. C. Barros, Z. Benkhaldoun, F. Bouchy, C. Briceño, D. A. Caldwell, K. A. Collins, Z. Essack, M. Ghachoui, M. Gillon, R. Hounsell, E. Jehin, J. M. Jenkins, M. A. F. Keniger, N. Law, A. W. Mann, L. D. Nielsen,
/ Abstract
The Neptunian desert and savanna have recently been found to be separated by a ridge, an overdensity of planets in the period range of $\simeq$3-5 days. These features are thought to be shaped by dynamical and atmospheric processes, but their roles are not yet well understood. Our aim was to confirm and characterize the super-Neptune TESS candidate TOI-5005.01, which orbits a moderately bright (V = 11.8) solar-type star (G2 V) with an orbital period of 6.3 days. We confirm TOI-5005 b to be a transiting super-Neptune with a radius of $R_{\rm p}$ = $6.25\pm 0.24$ $\rm R_{\rm \oplus}$ ($R_{\rm p}$ = $0.558\pm 0.021$ $\rm R_{\rm J}$) and a mass of $M_{\rm p}$ = $32.7\pm 5.9$ $\rm M_{\oplus}$ ($M_{\rm p}$ = $0.103\pm 0.018$ $\rm M_{\rm J}$), which corresponds to a mean density of $ρ_{\rm p}$ = $0.74 \pm 0.16$ $\rm g \, cm^{-3}$. Our internal structure modelling indicates that the overall metal mass fraction is well constrained to a value slightly lower than that of Neptune and Uranus ($Z_{\rm planet}$ = $0.76^{+0.04}_{-0.11}$). We also estimated the present-day atmospheric mass-loss rate of TOI-5005 b, but found contrasting predictions depending on the choice of photoevaporation model. At a population level, we find statistical evidence ($p$-value = $0.0092^{+0.0184}_{-0.0066}$) that planets in the savanna such as TOI-5005 b tend to show lower densities than planets in the ridge, with a dividing line around 1 $\rm g \, cm^{-3}$, which supports the hypothesis of different evolutionary pathways populating the two regimes. TOI-5005 b is located in a key region of the period-radius space to study the transition between the Neptunian ridge and the savanna. It orbits the brightest star of all such planets, which makes it a target of interest for atmospheric and orbital architecture observations that will bring a clearer picture of its overall evolution.