TOI-6038 A b: A dense sub-Saturn in the transition regime between the Neptunian ridge and savanna
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2025
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| author | Baliwal, Sanjay Sharma, Rishikesh Chakraborty, Abhijit Nikitha, K. J. Castro-González, A. Bhaskar, Hareesh G. Khandelwal, Akanksha Latham, David W. Bieryla, Allyson Bourrier, Vincent Prasad, Neelam J. S. S. V. Bharadwaj, Kapil K. Lad, Kevikumar A. Nayak, Ashirbad Joshi, Vishal Eastman, Jason D. |
| author_facet | Baliwal, Sanjay Sharma, Rishikesh Chakraborty, Abhijit Nikitha, K. J. Castro-González, A. Bhaskar, Hareesh G. Khandelwal, Akanksha Latham, David W. Bieryla, Allyson Bourrier, Vincent Prasad, Neelam J. S. S. V. Bharadwaj, Kapil K. Lad, Kevikumar A. Nayak, Ashirbad Joshi, Vishal Eastman, Jason D. |
| contents | 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 ($m_V=9.9$), metal-rich late F-type star, TOI-6038~A, with $T_{\rm{eff}}=6110\pm100~\mathrm{K}$, $\log{g}=4.118^{+0.015}_{-0.025}$, and $[{\rm{Fe/H}}]=0.124^{+0.079}_{-0.077}$ dex. The system also contains a wide-orbit binary companion, TOI-6038~B, an early K-type star at a projected separation of $\approx3217$ AU. We combined radial velocity data from PARAS-2 with photometric data from the Transiting Exoplanet Survey Satellite (TESS) for joint modeling. TOI-6038~A~b has a mass of $78.5^{+9.5}_{-9.9}~M_\oplus$ and a radius of $6.41^{+0.20}_{-0.16}~R_\oplus$, orbiting in a circular orbit with a period of $5.8267311^{+0.0000074}_{-0.0000068}$ days. Internal structure modeling suggests that $\approx74\%$ 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 $ρ_{\rm{P}}=1.62^{+0.23}_{-0.24}\rm~g\,cm^{-3}$, TOI-6038~A~b is compatible with the population of dense ridge planets ($ρ_{\rm{P}}\simeq$ 1.5-2.0 $\rm~g\,cm^{-3}$), 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. 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2501_02272 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | TOI-6038 A b: A dense sub-Saturn in the transition regime between the Neptunian ridge and savanna Baliwal, Sanjay Sharma, Rishikesh Chakraborty, Abhijit Nikitha, K. J. Castro-González, A. Bhaskar, Hareesh G. Khandelwal, Akanksha Latham, David W. Bieryla, Allyson Bourrier, Vincent Prasad, Neelam J. S. S. V. Bharadwaj, Kapil K. Lad, Kevikumar A. Nayak, Ashirbad Joshi, Vishal Eastman, Jason D. Earth and Planetary Astrophysics 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 ($m_V=9.9$), metal-rich late F-type star, TOI-6038~A, with $T_{\rm{eff}}=6110\pm100~\mathrm{K}$, $\log{g}=4.118^{+0.015}_{-0.025}$, and $[{\rm{Fe/H}}]=0.124^{+0.079}_{-0.077}$ dex. The system also contains a wide-orbit binary companion, TOI-6038~B, an early K-type star at a projected separation of $\approx3217$ AU. We combined radial velocity data from PARAS-2 with photometric data from the Transiting Exoplanet Survey Satellite (TESS) for joint modeling. TOI-6038~A~b has a mass of $78.5^{+9.5}_{-9.9}~M_\oplus$ and a radius of $6.41^{+0.20}_{-0.16}~R_\oplus$, orbiting in a circular orbit with a period of $5.8267311^{+0.0000074}_{-0.0000068}$ days. Internal structure modeling suggests that $\approx74\%$ 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 $ρ_{\rm{P}}=1.62^{+0.23}_{-0.24}\rm~g\,cm^{-3}$, TOI-6038~A~b is compatible with the population of dense ridge planets ($ρ_{\rm{P}}\simeq$ 1.5-2.0 $\rm~g\,cm^{-3}$), 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. 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. |
| title | TOI-6038 A b: A dense sub-Saturn in the transition regime between the Neptunian ridge and savanna |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2501.02272 |