| 1. |
- Hori, Yasunori, et al.
(författare)
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The Discovery and Follow-up of Four Transiting Short-period Sub-Neptunes Orbiting M Dwarfs
- 2024
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Ingår i: Astronomical Journal. - 1538-3881 .- 0004-6256. ; 167:6
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Tidskriftsartikel (refereegranskat)abstract
- Sub-Neptunes with radii of 2-3 R ⊕ are intermediate in size between rocky planets and Neptune-sized planets. The orbital properties and bulk compositions of transiting sub-Neptunes provide clues to the formation and evolution of close-in small planets. In this paper, we present the discovery and follow-up of four sub-Neptunes orbiting M dwarfs (TOI-782, TOI-1448, TOI-2120, and TOI-2406), three of which were newly validated by ground-based follow-up observations and statistical analyses. TOI-782 b, TOI-1448 b, TOI-2120 b, and TOI-2406 b have radii of R p = 2.740 − 0.079 + 0.082 R ⊕ , 2.769 − 0.068 + 0.073 R ⊕ , 2.120 ± 0.067 R ⊕, and 2.830 − 0.066 + 0.068 R ⊕ and orbital periods of P = 8.02, 8.11, 5.80, and 3.08 days, respectively. Doppler monitoring with the Subaru/InfraRed Doppler instrument led to 2σ upper limits on the masses of <19.1 M ⊕, <19.5 M ⊕, <6.8 M ⊕, and <15.6 M ⊕ for TOI-782 b, TOI-1448 b, TOI-2120 b, and TOI-2406 b, respectively. The mass-radius relationship of these four sub-Neptunes testifies to the existence of volatile material in their interiors. These four sub-Neptunes, which are located above the so-called “radius valley,” are likely to retain a significant atmosphere and/or an icy mantle on the core, such as a water world. We find that at least three of the four sub-Neptunes (TOI-782 b, TOI-2120 b, and TOI-2406 b), orbiting M dwarfs older than 1 Gyr, are likely to have eccentricities of e ∼ 0.2-0.3. The fact that tidal circularization of their orbits is not achieved over 1 Gyr suggests inefficient tidal dissipation in their interiors.
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| 2. |
- Esparza-Borges, E., et al.
(författare)
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A hot sub-Neptune in the desert and a temperate super-Earth around faint M dwarfs Color validation of TOI-4479b and TOI-2081b
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 666
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We report the discovery and validation of two TESS exoplanets orbiting faint M dwarfs: TOI-4479b and TOI-2081b. Methods. We jointly analyzed space (TESS mission) and ground-based (MuSCAT2, MuSCAT3 and SINISTRO instruments) light curves using our multicolor photometry transit analysis pipeline. This allowed us to compute contamination limits for both candidates and validate them as planet-sized companions. Results. We found TOI-4479b to be a sub-Neptune-sized planet (R-p = 2.82(-0.63)(+0.65) R-circle plus) and TOI-2081b to be a super-Earth-sized planet (R-p = 2.04(-0.54)(+0.50) R-circle plus). Furthermore, we obtained that TOI-4479b, with a short orbital period of 1.15890(-0.00001)(+0.00002) days, lies within the Neptune desert and is in fact the largest nearly ultra-short period planet around an M dwarf known to date. Conclusions. These results make TOI-4479b rare among the currently known exoplanet population of M dwarf stars and an especially interesting target for spectroscopic follow-up and future studies of planet formation and evolution.
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| 3. |
- Morello, Giuseppe, 1989, et al.
(författare)
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TOI-1442 b and TOI-2445 b: Two potentially rocky ultra-short period planets around M dwarfs
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 673
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Tidskriftsartikel (refereegranskat)abstract
- Context. Exoplanets with orbital periods of less than one day are known as ultra-short period (USP) planets. They are relatively rare products of planetary formation and evolution processes, but especially favourable for characterisation with current planet detection methods. At the time of writing, 125 USP planets have already been confirmed. Aims. Our aim is to validate the planetary nature of two new transiting planet candidates around M dwarfs announced by the NASA Transiting Exoplanet Survey Satellite (TESS), registered as TESS Objects of Interest (TOIs) TOI-1442.01 and TOI-2445.01. Methods. We used TESS data, ground-based photometric light curves, and Subaru/IRD spectrograph radial velocity (RV) measurements to validate both planetary candidates and to establish their physical properties. Results. TOI-1442 b is a validated exoplanet with an orbital period of P = 0.4090682 ± 0.0000004 day, a radius of Rp = 1.15 ± 0.06 R☉, and equilibrium temperature of Tp,eq = 1357+−4942 K. TOI-2445 b is also validated with an orbital period of P = 0.3711286 ± 0.0000004 day, a radius of Rp = 1.33 ± 0.09 R☉, and equilibrium temperature of Tp,eq = 1330+−6156 K. Their physical properties align with current empirical trends and formation theories of USP planets. Based on the RV measurements, we set 3σ upper mass limits of 8 M☉ and 20 M☉, thus confirming the non-stellar, sub-Jovian nature of both transiting objects. More RV measurements will be needed to constrain the planetary masses and mean densities, and the predicted presence of outer planetary companions. These targets extend the small sample of USP planets orbiting around M dwarfs up to 21 members. They are also among the 20 most suitable terrestrial planets for atmospheric characterisation via secondary eclipse with the James Webb Space Telescope, according to a widespread emission spectroscopy metric.
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| 4. |
- Kawauchi, K., et al.
(författare)
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Validation and atmospheric exploration of the sub-Neptune TOI-2136b around a nearby M3 dwarf
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 666
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Tidskriftsartikel (refereegranskat)abstract
- Context. The NASA space telescope TESS is currently in the extended mission of its all-sky search for new transiting planets. Of the thousands of candidates that TESS is expected to deliver, transiting planets orbiting nearby M dwarfs are particularly interesting targets since they provide a great opportunity to characterize their atmospheres by transmission spectroscopy. Aims. We aim to validate and characterize the new sub-Neptune-sized planet candidate TOI-2136.01 orbiting a nearby M dwarf (d = 33.36 +/- 0.02 pc, T-eff = 3373 +/- 108 K) with an orbital period of 7.852 days. Methods. We use TESS data, ground-based multicolor photometry, and radial velocity measurements with the InfraRed Doppler (IRD) instrument on the Subaru Telescope to validate the planetary nature of TOI-2136.01, and estimate the stellar and planetary parameters. We also conduct high-resolution transmission spectroscopy to search for helium in its atmosphere. Results. We confirm that TOI-2136.01 (now named TOI-2136b) is a bona fide planet with a planetary radius of R-p = 2.20 +/- 0.07 R-circle plus and a mass of M-p = 4.7(-2.6)(+3.1) M-circle plus. We also search for helium 10830 angstrom absorption lines and place an upper limit on the equivalent width of <7.8 m angstrom and on the absorption signal of <1.44% with 95% confidence. Conclusions. TOI-2136b is a sub-Neptune transiting a nearby and bright star (J = 10.8 mag), and is a potentially hycean planet, which is a new class of habitable planets with large oceans under a H-2-rich atmosphere, making it an excellent target for atmospheric studies to understand the formation, evolution, and habitability of the small planets.
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