TOI-2084 b and TOI-4184 b: Two new sub-Neptunes around M dwarf stars

Barkaoui, Khalid; Timmermans, Mathilde; Soubkiou, Abderahmane

doi:10.1051/0004-6361/202346838

A&A

2023

DOI: 10.1051/0004-6361/202346838

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TOI-2084 b and TOI-4184 b: Two new sub-Neptunes around M dwarf stars

Khalid Barkaoui¹,

Mathilde Timmermans²,

Abderahmane Soubkiou³

Abstract: We present the discovery and validation of two TESS exoplanets orbiting nearby M dwarfs: TOI-2084 b, and TOI-4184b. We characterized the host stars by combining spectra from Shane/Kast and Magellan/FIRE, spectral energy distribution analysis, and stellar evolutionary models. In addition, we used Gemini-South/Zorro & -North/Alopeke high-resolution imaging, archival science images, and statistical validation packages to support the planetary interpretation. We performed a global analysis of multi-colour phot… Show more

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2024

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Cited by 5 publications

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TOI-4336 A b: A temperate sub-Neptune ripe for atmospheric characterization in a nearby triple M-dwarf system

Timmermans,

Dransfield,

Gillon

et al. 2024

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Small planets transiting bright nearby stars are essential to our understanding of the formation and evolution of exoplanetary systems. However, few constitute prime targets for atmospheric characterization, and even fewer are part of multiple star systems. This work aims to validate TOI-4336 A b, a sub-Neptune-sized exoplanet candidate identified by the space-based transit survey around a nearby M dwarf. We validated the planetary nature of TOI-4336 A b through the global analysis of TESS and follow-up multi-band high-precision photometric data from ground-based telescopes, medium- and high-resolution spectroscopy of the host star, high-resolution speckle imaging, and archival images. The newly discovered exoplanet TOI-4336 A b has a radius of 2.1pm 0.1R$_ oplus $. Its host star is an M3.5 -dwarf star with a mass of 0.33pm 0.01M$_ odot $ and a radius of 0.33pm 0.02R$_ odot $, and is a member of a hierarchical triple M-dwarf system 22 pc away from the Sun. The planet's orbital period of 16.3 days places it at the inner edge of the habitable zone of its host star, which is the brightest of the inner binary pair. The parameters of the system make TOI-4336 A b an extremely promising target for the detailed atmospheric characterization of a temperate sub-Neptune by transit transmission spectroscopy with jwst.

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TOI-4336 A b: A temperate sub-Neptune ripe for atmospheric characterization in a nearby triple M-dwarf system

Timmermans,

Dransfield,

Gillon

et al. 2024

A&A

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Characterising TOI-732 b and c: New insights into the M-dwarf radius and density valley

Bonfanti,

Brady,

Wilson

et al. 2024

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TOI-732 is an M dwarf hosting two transiting planets that are located on the two opposite sides of the radius valley. Inferring a reliable demographics for this type of systems is key to understanding their formation and evolution mechanisms. By doubling the number of available space-based observations and increasing the number of radial velocity (RV) measurements, we aim at refining the parameters of TOI-732\,b and c. We also use the results to study the slope of the radius valley and the density valley for a well-characterised sample of M-dwarf exoplanets. We performed a global Markov chain Monte Carlo analysis by jointly modelling ground-based light curves and CHEOPS and TESS observations, along with RV time series both taken from the literature and obtained with the MAROON-X spectrograph. The slopes of the M-dwarf valleys were quantified via a support vector machine (SVM) procedure. TOI-732\,b is an ultrashort-period planet $ d) with a radius $R_b=1.325_ oplus $, a mass $M_b=2.46 oplus $, and thus a mean density $ $, while the outer planet at $P=12.252284 d has oplus $, $M_c=8.04_ oplus $, and thus $ $. Even with respect to the most recently reported values, this work yields uncertainties on the transit depths and on the RV semi-amplitudes that are smaller up to a factor of sim \,1.6 and sim \,2.4 for TOI-732\,b and c, respectively. Our calculations for the interior structure and the location of the planets in the mass-radius diagram lead us to classify TOI-732\,b as a super-Earth and TOI-732\,c as a mini-Neptune. Following the SVM approach, we quantified $ $, which is flatter than for Sun-like stars. In line with former analyses, we note that the radius valley for M-dwarf planets is more densely populated, and we further quantify the slope of the density valley as $ Compared to FGK stars, the weaker dependence of the position of the radius valley on the orbital period might indicate that the formation shapes the radius valley around M dwarfs more strongly than the evolution mechanisms.

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TOI-4438 b: a transiting mini-Neptune amenable to atmospheric characterization

Goffo,

Chaturvedi,

Murgas

et al. 2024

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We report the confirmation and mass determination of a mini-Neptune transiting the M3.5\,V star TOI-4438 (G 182-34) every 7.44 days. A transit signal was detected with NASA's TESS space mission in the sectors 40, 52, and 53. In order to validate the planet TOI-4438\,b and to determine the system properties, we combined TESS data with high-precision radial velocity measurements from the CARMENES spectrograph, spanning almost one year, and ground-based transit photometry. We found that TOI-4438\,b has a radius of $R_ b $\,=\,2.52\,pm \,0.13 R$_ (5<!PCT!> precision), which together with a mass of $M_ b $\,=\,5.4\,pm \,1.1 M$_ (20<!PCT!> precision), results in a bulk density of $ b $ (sim 28<!PCT!> precision), aligning the discovery with a volatile-rich planet. Our interior structure retrieval with a pure water envelope yields a minimum water mass fraction of 46<!PCT!> (1sigma ). TOI-4438\,b is a volatile-rich mini-Neptune with likely H/He mixed with molecules, such as water, CO$_2$, and CH$_4$. The primary star has a $J$-band magnitude of 9.7, and the planet has a high transmission spectroscopy metric (TSM) of 136\,pm \,13. Taking into account the relatively warm equilibrium temperature of $T_ eq $\,=\,435\,pm \,15 K, and the low activity level of its host star, TOI-4438\,b is one of the most promising mini-Neptunes around an M dwarf for transmission spectroscopy studies.

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TOI-2084 b and TOI-4184 b: Two new sub-Neptunes around M dwarf stars

Cited by 5 publications

References 100 publications

TOI-4336 A b: A temperate sub-Neptune ripe for atmospheric characterization in a nearby triple M-dwarf system

TOI-4336 A b: A temperate sub-Neptune ripe for atmospheric characterization in a nearby triple M-dwarf system

Characterising TOI-732 b and c: New insights into the M-dwarf radius and density valley

TOI-4438 b: a transiting mini-Neptune amenable to atmospheric characterization

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