Mass–Radius Relationship for M Dwarf Exoplanets: Comparing Nonparametric and Parametric Methods

Kanodia, Shubham; Wolfgang, Angie; Stefánsson, Guðmundur; Ning, Bo; Mahadevan, Suvrath

doi:10.3847/1538-4357/ab334c

Cited by 59 publications

(55 citation statements)

References 65 publications

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“…We also predict some properties based on the estimated planet mass. We compared planetary masses predicted by the mass-radius relationships of Chen & Kipping (2017), Ning et al (2018) and Kanodia et al (2019). We find the mass posteriors of both Ning et al (2018) and Kanodia et al (2019) are considerably lower than for Chen & Kipping (2017), and extend down to unphysically low masses.…”

Section: Resultsmentioning

confidence: 84%

A large sub-Neptune transiting the thick-disk M4 V TOI-2406

Wells

Rackham

Schanche

et al. 2021

A&A

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Context. Large sub-Neptunes are uncommon around the coolest stars in the Galaxy and are rarer still around those that are metal-poor. However, owing to the large planet-to-star radius ratio, these planets are highly suitable for atmospheric study via transmission spectroscopy in the infrared, such as with JWST. Aims. Here we report the discovery and validation of a sub-Neptune orbiting the thick-disk, mid-M dwarf star TOI-2406. The star’s low metallicity and the relatively large size and short period of the planet make TOI-2406 b an unusual outcome of planet formation, and its characterisation provides an important observational constraint for formation models. Methods. We first infer properties of the host star by analysing the star’s near-infrared spectrum, spectral energy distribution, and Gaia parallax. We use multi-band photometry to confirm that the transit event is on-target and achromatic, and we statistically validate the TESS signal as a transiting exoplanet. We then determine physical properties of the planet through global transit modelling of the TESS and ground-based time-series data. Results. We determine the host to be a metal-poor M4 V star, located at a distance of 56 pc, with properties Teff = 3100 ± 75 K, M* = 0.162 ± 0.008M⊙, R* = 0.202 ± 0.011R⊙, and [Fe∕H] = −0.38 ± 0.07, and a member of the thick disk. The planet is a relatively large sub-Neptune for the M-dwarf planet population, with Rp = 2.94 ± 0.17R⊕ and P= 3.077 d, producing transits of 2% depth. We note the orbit has a non-zero eccentricity to 3σ, prompting questions about the dynamical history of the system. Conclusions. This system is an interesting outcome of planet formation and presents a benchmark for large-planet formation around metal-poor, low-mass stars. The system warrants further study, in particular radial velocity follow-up to determine the planet mass and constrain possible bound companions. Furthermore, TOI-2406 b is a good target for future atmospheric study through transmission spectroscopy. Although the planet’s mass remains to be constrained, we estimate the S/N using amass-radius relationship, ranking the system fifth in the population of large sub-Neptunes, with TOI-2406 b having a much lower equilibrium temperature than other spectroscopically accessible members of this population.

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Section: Resultsmentioning

confidence: 84%

A large sub-Neptune transiting the thick-disk M4 V TOI-2406

Wells

Rackham

Schanche

et al. 2021

A&A

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“…There have been numerous studies which find differences in the occurrence rates for planets around M dwarfs versus earlier type stars (Hardegree-Ullman et al 2019;Hsu et al 2020), as well as the empirical distributions of mass and radius for said planets (Bonfils et al 2013;Dressing & Charbonneau 2015). These results motivate independent statistical studies of M-dwarf exoplanet populations (Cloutier & Menou 2020;Kanodia et al 2019). However, the aforementioned studies suffer from a small M-dwarf planet sample.…”

Section: Toi-1728b In M-dwarf Planet Parameter Spacementioning

confidence: 91%

TOI-1728b: The Habitable-zone Planet Finder Confirms a Warm Super-Neptune Orbiting an M-dwarf Host

Kanodia

Cañas

Stefánsson

et al. 2020

ApJ

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We confirm the planetary nature of TOI-1728b using a combination of ground-based photometry, near-infrared Doppler velocimetry and spectroscopy with the Habitable-zone Planet Finder. TOI-1728 is an old, inactive M0 star with T eff =-+ 3980 32 31 K, which hosts a transiting super-Neptune at an orbital period of ∼3.49 days. Joint fitting of the radial velocities and TESS and ground-based transits yields a planetary radius of-+ 5.05 0.17 0.16 R ⊕ , mass-+ 26.78 5.13 5.43 M ⊕ , and eccentricity-+ 0.057 0.039 0.054. We estimate the stellar properties, and perform a search for He 10830 Åabsorption during the transit of this planet and claim a null detection with an upper limit of 1.1% with 90% confidence. A deeper level of He 10830 Åabsorption has been detected in the planet atmosphere of GJ 3470b, a comparable gaseous planet. TOI-1728b is the largest super-Neptune-the intermediate subclass of planets between Neptune and the more massive gas-giant planets-discovered around an M dwarf. With its relatively large mass and radius, TOI-1728 represents a valuable data point in the M-dwarf exoplanet mass-radius diagram, bridging the gap between the lighter Neptune-sized planets and the heavier Jovian planets known to orbit M dwarfs. With a low bulk density of-+ 1.14 0.24 0.26 g cm −3 , and orbiting a bright host star (J∼9.6, V∼12.4), TOI-1728b is also a promising candidate for transmission spectroscopy both from the ground and from space, which can be used to constrain planet formation and evolutionary models.

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“…For simplicity, we assumed the best-case scenario, namely zero (mutual) inclinations and zero eccentricities of the planetary orbits. We estimate the planetary masses from the observed radius using the MRExo package 14 , which performs non-parametric fitting of the mass-radius relation (Ning et al 2018;Kanodia et al 2019). Our dynamical stability pipeline is described as follows.…”

Section: Multi-planet System Stabilitymentioning

confidence: 99%

37 new validated planets in overlapping K2 campaigns

Leon

Livingston

Endl

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We analysed 68 candidate planetary systems first identified during Campaigns 5 and 6 (C5 and C6) of the NASA K2 mission. We set out to validate these systems by using a suite of follow-up observations, including adaptive optics, speckle imaging, and reconnaissance spectroscopy. The overlap between C5 with C16 and C18, and C6 with C17, yields lightcurves with long baselines that allow us to measure the transit ephemeris very precisely, revisit single transit candidates identified in earlier campaigns, and search for additional transiting planets with longer periods not detectable in previous works. Using vespa, we compute false positive probabilities of less than 1% for 37 candidates orbiting 29 unique host stars and hence statistically validate them as planets. These planets have a typical size of 2.2 R⊕ and orbital periods between 1.99 and 52.71 days. We highlight interesting systems including a sub-Neptune with the longest period detected by K2, sub-Saturns around F stars, several multi-planetary systems in a variety of architectures. These results show that a wealth of planetary systems still remains in the K2 data, some of which can be validated using minimal follow-up observations and taking advantage of analyses presented in previous catalogs.

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Mass–Radius Relationship for M Dwarf Exoplanets: Comparing Nonparametric and Parametric Methods

Cited by 59 publications

References 65 publications

A large sub-Neptune transiting the thick-disk M4 V TOI-2406

A large sub-Neptune transiting the thick-disk M4 V TOI-2406

TOI-1728b: The Habitable-zone Planet Finder Confirms a Warm Super-Neptune Orbiting an M-dwarf Host

37 new validated planets in overlapping K2 campaigns

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