The GAPS programme at TNG. XLIX. TOI-5398, the youngest compact multi-planet system composed of an inner sub-Neptune and an outer warm Saturn
Journal
Date Issued
2024
Author(s)
Mantovan, G.
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Zingales, T.
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Piotto, G.
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Polychroni, D.
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Baratella, M.
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Nardiello, D.
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Stassun, K.
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John, A. Anna
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Watkins, C.
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Bieryla, A.
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Lissauer, J. J.
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Twicken, J. D.
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Winn, J. N.
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Montalto, M.
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Boffin, H.
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Cheryasov, D.
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Strakhov, I.
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Murgas, F.
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D'Arpa, M.
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Barkaoui, K.
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Benni, P.
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Cabona, L.
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Cameron, A. C.
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Cochran, W.
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Collins, K. A.
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Dong, J.
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Endl, M.
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Fukui, A.
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Fűrész, G.
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Gandolfi, D.
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Ghedina, A.
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Jenkins, J.
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Kabáth, P.
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Latham, D. W.
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Lorenzi, V.
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Luque, R.
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McLeod, K.
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Narita, N.
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Nowak, G.
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Orell-Miquel, J.
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Pallé, E.
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Parviainen, H.
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Pedani, M.
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Quinn, S. N.
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Relles, H.
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Rowden, P.
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Schwarz, R.
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Seager, S.
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Shporer, A.
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Vanderburg, A.
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Wilson, T. G.
Abstract
Context. Short-period giant planets (P ≲ 10 days, Mp >0.1 MJ) are frequently found to be solitary compared to other classes of exo-planets. Small inner companions to giant planets with P ≲ 15 days are known only in five compact systems: WASP-47, Kepler-730, WASP-132, TOI-1130, and TOI-2000. Here, we report the confirmation of TOI-5398, the youngest known compact multi-planet system composed of a hot sub-Neptune (TOI-5398 c, Pc = 4.77271 days) orbiting interior to a short-period Saturn (TOI-5398 b, Pb = 10.590547 days) planet, both transiting around a 650 ± 150 Myr G-type star.
Aims: As part of the Global Architecture of Planetary Systems (GAPS) Young Object project, we confirmed and characterised this compact system, measuring the radius and mass of both planets, thus constraining their bulk composition.
Methods: Using multi-dimensional Gaussian processes, we simultaneously modelled stellar activity and planetary signals from the Transiting Exoplanet Survey Satellite (TESS) Sector 48 light curve and our High Accuracy Radial velocity Planet Searcher (HARPS-N) radial velocity (RV) time series. We confirmed the planetary nature of both planets, TOI-5398 b and TOI-5398 c, and obtained a precise estimation of their stellar parameters.
Results: Through the use of astrometric, photometric, and spectroscopic observations, our findings indicate that TOI-5398 is a young, active G dwarf star (650 ± 150 Myr) with a rotational period of Prot = 7.34 days. The transit photometry and RV measurements enabled us to measure both the radius and mass of planets b, Rb = 10.30 ± 0.40 R⊕, Mb = 58.7 ± 5.7 M⊕, and c, Rc = 3.52 ± 0.19 R⊕, Mc = 11.8 ± 4.8 M⊕. TESS observed TOI-5398 during sector 48 and no further observations are planned in the current Extended Mission, making our ground-based light curves crucial for improvement of the ephemeris. With a transmission spectroscopy metric (TSM) value of around 300, TOI-5398 b is the most amenable warm giant (10 < P < 100 days) for JWST atmospheric characterisation.
Aims: As part of the Global Architecture of Planetary Systems (GAPS) Young Object project, we confirmed and characterised this compact system, measuring the radius and mass of both planets, thus constraining their bulk composition.
Methods: Using multi-dimensional Gaussian processes, we simultaneously modelled stellar activity and planetary signals from the Transiting Exoplanet Survey Satellite (TESS) Sector 48 light curve and our High Accuracy Radial velocity Planet Searcher (HARPS-N) radial velocity (RV) time series. We confirmed the planetary nature of both planets, TOI-5398 b and TOI-5398 c, and obtained a precise estimation of their stellar parameters.
Results: Through the use of astrometric, photometric, and spectroscopic observations, our findings indicate that TOI-5398 is a young, active G dwarf star (650 ± 150 Myr) with a rotational period of Prot = 7.34 days. The transit photometry and RV measurements enabled us to measure both the radius and mass of planets b, Rb = 10.30 ± 0.40 R⊕, Mb = 58.7 ± 5.7 M⊕, and c, Rc = 3.52 ± 0.19 R⊕, Mc = 11.8 ± 4.8 M⊕. TESS observed TOI-5398 during sector 48 and no further observations are planned in the current Extended Mission, making our ground-based light curves crucial for improvement of the ephemeris. With a transmission spectroscopy metric (TSM) value of around 300, TOI-5398 b is the most amenable warm giant (10 < P < 100 days) for JWST atmospheric characterisation.
Table A.1 is available at the CDS ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/682/A129
Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated by the Fundación Galileo Galilei (FGG) of the Istituto Nazionale di Astrofisica (INAF) at the Observatorio del Roque de los Muchachos (La Palma, Canary Islands, Spain).
Flatiron Research Fellow.
NASA Sagan Fellow.
Volume
682
Start page
A129
Issn Identifier
0004-6361
Ads BibCode
2024A&A...682A.129M
Rights
open.access
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