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The GAPS programme at TNG. XL. A puffy and warm Neptune-sized planet and an outer Neptune-mass candidate orbiting the solar-type star TOI-1422

Abstract : Context. Neptunes represent one of the main types of exoplanets and have chemical-physical characteristics halfway between rocky and gas giant planets. Therefore, their characterization is important for understanding and constraining both the formation mechanisms and the evolution patterns of planets.
Aims: We investigate the exoplanet candidate TOI-1422 b, which was discovered by the TESS space telescope around the high proper-motion G2 V star TOI-1422 (V = 10.6 mag), 155 pc away, with the primary goal of confirming its planetary nature and characterising its properties.
Methods: We monitored TOI-1422 with the HARPS-N spectrograph for 1.5 yr to precisely quantify its radial velocity (RV) variation. We analyse these RV measurements jointly with TESS photometry and check for blended companions through high-spatial resolution images using the AstraLux instrument.
Results: We estimate that the parent star has a radius of R = 1.019−0.013+0.014 R, and a mass of M = 1.019−0.013+0.014 M. Our analysis confirms the planetary nature of TOI-1422 b and also suggests the presence of a Neptune-mass planet on a more distant orbit, the candidate TOI-1422 c, which is not detected in TESS light curves. The inner planet, TOI-1422 b, orbits on a period of Pb = 12.9972 ± 0.0006 days and has an equilibrium temperature of Teq,b = 867 ± 17 K. With a radius of Rb = 3.96−0.11+0.13 R, a mass of Mb = 9.0−2.0+2.3 M and, consequently, a density of ρb = 0.795−0.235+0.290g cm−3, it can be considered a warm Neptune-sized planet. Compared to other exoplanets of a similar mass range, TOI-1422 b is among the most inflated, and we expect this planet to have an extensive gaseous envelope that surrounds a core with a mass fraction around 10% - 25% of the total mass of the planet. The outer non-transiting planet candidate, TOI-1422 c, has an orbital period of Pc = 29.29−0.20+0.21 days, a minimum mass, Mcsin i, of 11.1−2.3+2.6 M, an equilibrium temperature of Teq,c = 661 ± 13 K and, therefore, if confirmed, could be considered as another warm Neptune.
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Submitted on : Saturday, November 19, 2022 - 8:45:46 AM
Last modification on : Sunday, November 20, 2022 - 3:05:03 AM

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L. Naponiello, L. Mancini, M. Damasso, A. S. Bonomo, A. Sozzetti, et al.. The GAPS programme at TNG. XL. A puffy and warm Neptune-sized planet and an outer Neptune-mass candidate orbiting the solar-type star TOI-1422. Astronomy and Astrophysics - A&A, 2022, 667, ⟨10.1051/0004-6361/202244079⟩. ⟨insu-03860268⟩

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