2025AJ....169..147B -
Astron. J., 169, 147 (2025/March-0)
TOI-6038 A b: A Dense Sub-Saturn in the Transition Regime between the Neptunian Ridge and Savanna.
BALIWAL S., SHARMA R., CHAKRABORTY A., NIKITHA K.J., CASTRO-GONZALEZ A., BHASKAR H.G., KHANDELWAL A., LATHAM D.W., BIERYLA A., BOURRIER V., PRASAD N.J.S.S.V., BHARADWAJ K.K., LAD K.A., NAYAK A., JOSHI V. and EASTMAN J.D.
Abstract (from CDS):
We present the discovery and characterization of a sub-Saturn exoplanet, TOI-6038 A b, using the PARAS-2 spectrograph. The planet orbits a bright (mV = 9.9), metal-rich late F-type star, TOI-6038 A, with Teff = 6110 ± 100 K, $\mathrm{log}\,g=4.11{8}_{-0.025}^{+0.015}$, and $[{\rm{Fe/H}}]=0.12{4}_{-0.077}^{+0.079}$ dex. The system also contains a wide-orbit binary companion, TOI-6038 B, an early K-type star at a projected separation of ≈3217 au. We combined radial velocity data from PARAS-2 with photometric data from the Transiting Exoplanet Survey Satellite for joint modeling. TOI-6038 A b has a mass of $78.{5}_{-9.9}^{+9.5}\,{M}_{\oplus }$ and a radius of $6.4{1}_{-0.16}^{+0.20}\,{R}_{\oplus }$, orbiting in a circular orbit with a period of $5.826731{1}_{-0.0000068}^{+0.0000074}$ days. Internal structure modeling suggests that ≈74% of the planet's mass is composed of dense materials, such as rock and iron, forming a core, while the remaining mass consists of a low-density H/He envelope. TOI-6038 A b lies at the transition regime between the recently identified Neptunian ridge and savanna. Having a density of ${\rho }_{{\rm{P}}}=1.6{2}_{-0.24}^{+0.23}\,{{\rm{g}}\,{\rm{cm}}}^{-3}$, TOI-6038 A b is compatible with the population of dense ridge planets (ρP ≃ 1.5-2.0 g cm–3), which have been proposed to have reached their close-in locations through high-eccentricity tidal migration (HEM). First-order estimates suggest that the secular perturbations induced by TOI-6038 B may be insufficient to drive the HEM of TOI-6038 A b. Therefore, it is not clear whether HEM driven by a still undetected companion or early disk-driven migration brought TOI-6038 A b to its present-day close-in orbit. Interestingly, its bright host star makes TOI-6038 A b a prime target for atmospheric escape and orbital architecture observations, which will help us to better understand its overall evolution.
Abstract Copyright:
© 2025. The Author(s). Published by the American Astronomical Society.
Journal keyword(s):
Exoplanet systems - Wide binary stars - Transit photometry - Radial velocity - Extrasolar gaseous planets - Exoplanet dynamics
Simbad objects:
6
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