Proyecto de Investigación: Exoplanets in Transit and their Atmosphere
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337591
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Planetary system LHS 1140 revisited with ESPRESSO and TESS
(EDP Sciences, 2020-10-15) Lillo Box, J.; Figueira, P.; Leleu, A.; Acuña, L.; Faria, J. P.; Harada, N.; Santos, Nuno C.; Correia, A. C. M.; Robutel, P.; Deleuil, M.; Barrado, David; Sousa, S. G.; Bonfils, Xavier; Mousis, O.; Almenara, J. M.; Astudillo Defru, N.; Marcq, E.; Udry, S.; Lovis, C.; Pepe, Francesco; Fundacao para a Ciencia e a Tecnologia (FCT); Agencia Estatal de Investigación (AEI); Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT); European Commission (EC); Faria, J. [0000-0002-6728-244X]; Correia, A. C. M. [0000-0002-8946-8579]; Leleu, A. [0000-0003-2051-7974]; Lillo Box, J. [0000-0003-3742-1987]; Santos, N. [0000-0003-4422-2919]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. LHS 1140 is an M dwarf known to host two transiting planets at orbital periods of 3.77 and 24.7 days. They were detected with HARPS and Spitzer. The external planet (LHS 1140 b) is a rocky super-Earth that is located in the middle of the habitable zone of this low-mass star. All these properties place this system at the forefront of the habitable exoplanet exploration, and it therefore constitutes a relevant case for further astrobiological studies, including atmospheric observations.
Aims. We further characterize this system by improving the physical and orbital properties of the known planets, search for additional planetary-mass components in the system, and explore the possibility of co-orbitals.
Methods. We collected 113 new high-precision radial velocity observations with ESPRESSO over a 1.5-yr time span with an average photon-noise precision of 1.07 m s−1. We performed an extensive analysis of the HARPS and ESPRESSO datasets and also analyzed them together with the new TESS photometry. We analyzed the Bayesian evidence of several models with different numbers of planets and orbital configurations.
Results. We significantly improve our knowledge of the properties of the known planets LHS 1140 b (Pb ~ 24.7 days) and LHS 1140 c (Pc ~ 3.77 days). We determine new masses with a precision of 6% for LHS 1140 b (6.48 ± 0.46 M⊕) and 9% for LHS 1140 c (mc = 1.78 ± 0.17 M⊕). This reduces the uncertainties relative to previously published values by half. Although both planets have Earth-like bulk compositions, the internal structure analysis suggests that LHS 1140 b might be iron-enriched and LHS 1140 c might be a true Earth twin. In both cases, the water content is compatible to a maximum fraction of 10–12% in mass, which is equivalent to a deep ocean layer of 779 ± 650 km for the habitable-zone planet LHS 1140 b. Our results also provide evidence for a new planet candidate in the system (md = 4.8 ± 1.1M⊕) on a 78.9-day orbital period, which is detected through three independent methods. The analysis also allows us to discard other planets above 0.5 M⊕ for periods shorter than 10 days and above 2 M⊕ for periods up to one year. Finally, our co-orbital analysis discards co-orbital planets in the tadpole and horseshoe configurations of LHS 1140 b down to 1 M⊕ with a 95% confidence level (twice better than with the previous HARPS dataset). Indications for a possible co-orbital signal in LHS 1140 c are detected in both radial velocity (alternatively explained by a high eccentricity) and photometric data (alternatively explained by systematics), however.
Conclusions. The new precise measurements of the planet properties of the two transiting planets in LHS 1140 as well as the detection of the planet candidate LHS 1140 d make this system a key target for atmospheric studies of rocky worlds at different stellar irradiations.
Sibling sub-Neptunes around sibling M dwarfs: TOI-521 and TOI-912
(EDP Sciences, 2026-01-27) Lacedelli, G.; Pallé, E.; Luque, R.; Ikuta, Kai; Tabernero, H. M.; Zapatero Osorio, María Rosa; Almenara, J. M.; Pozuelos, F. J.; Jankowski, Dawid; Narita, N.; Fukui, A.; Nowak, G.; Hirano, T.; Ishikawa, Hiroyuki Tako; Kimura, Tadahiro; Hori, Y.; Collins, K. A.; Howell, Steve B.; Jiang, Chengzi; Murgas Alcaino, F.; Osborn, Hugh P., Hugh; Astudillo Defru, N.; Bonfils, Xavier; Charbonneau, D.; Fausnaugh, M. M.; Geraldía González, Samuel; Goździewski, Krzysztof; Guerra, P.; Hayashi, Yuya; Hodapp, K.; Horne, K.; Isogai, K.; Jafariyazani, M.; Kagetani, T.; Kawai, Y.; Kawauchi, K.; Krishnamurthy, V.; Kotani, T.; Kudo, T.; Kurokawa, Takashi; Kuzuhara, M.; Mori, M.; Nishikawa, Jun; Nugroho, Stevanus Kristianto; Omiya, M.; Schwarz, R. P.; Sefako, Ramotholo; Shporer, A.; Srdoc, G.; Teng, Huan-Yu; Watanabe, N.; Agencia Estatal de Investigación (España); National Aeronautics and Space Administration (NASA); European Research Council (ERC); Swiss National Science Foundation (SNSF); Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)
Context. Sub-Neptunes are absent in the Solar System, yet they are the most common category of planets found in our Galaxy. This kind of planet challenges the internal structure models, prompts investigations into its formation and evolution, and pushes atmospheric characterisation studies to break the degeneracy in their inner composition.
Aims. We report here the discovery and characterisation of new sub-Neptunes orbiting two similar M dwarfs, TOI-521 (Teff = 3544 ± 100 K, V = 14.7 mag) and TOI-912 (Teff = 3572 ± 100 K, V = 12.7 mag). Each star hosts a transiting planetary candidate identified by TESS and is part of the THIRSTEE follow-up programme, which aims to understand the sub-Neptune population through in-depth and precise characterisation studies on a population level.
Methods. We analysed TESS light curves, ground-based photometry, and high-precision ESPRESSO, HARPS, and IRD radial velocities to confirm the planetary nature of both candidates, infer the precise orbital and physical parameters of the planets, and investigate the presence of additional planets in the systems.
Results. The two stars host nearly identical planets in terms of mass and radius. TOI-521 hosts a transiting sub-Neptune in a 1.5-day orbit with radius and mass of Rb = 1.98 ± 0.14 R⊕ and Mb = 5.3 ± 1.0 M⊕, respectively. Moreover, we identified an additional candidate at 20.3 days, with a minimum mass of Mp sin i = 10.7−2.4+2.5 M⊕, currently not detected as transiting in our photometric dataset. Similarly, the planet orbiting TOI-912 is a 4.7-d sub-Neptune with Rb = 1.93 ± 0.13 R⊕ and Mb = 5.1 ± 0.5 M⊕. Interestingly, TOI-912 b likely possesses an unusually high eccentricity (e = 0.58 ± 0.02) and is probably undergoing strong tidal dissipation. If such eccentricity were confirmed, it would make TOI-912 b one of the most eccentric sub-Neptunes known to date. TOI-521 b and TOI-912 b have very similar densities (~4 g cm−3), and they lie in the degenerate region of the mass-radius diagram where different compositions are plausible, including a volatile-rich composition, or a rocky core surrounded by a H-He envelope. When compared to the other THIRSTEE M-dwarf targets, our sample supports the division of sub-Neptunes into two distinct populations divided by a density gap. Both planets are interesting targets for atmospheric follow-up in the context of understanding the temperature-atmospheric feature trend that starts to emerge thanks to JWST observations.
