Introduction

Cox, Damian; Caze, Marguerite La; Levine, Michael P.

doi:10.4324/9781315192161-1

Cited by 3 publications

(3 citation statements)

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“…Wright et al 2011), indicating that 𝐿 sat HE ∝ 𝐿 bol ∝ 𝑀 3.2 * (e.g. Cox 2000). The scaling of 𝑡 sat with stellar mass is less certain, although it does increase as the stellar mass decreases (e.g.…”

Section: Expected Location Of the M Dwarf Radius Valleymentioning

confidence: 99%

Masses and compositions of three small planets orbiting the nearby M dwarf L231-32 (TOI-270) and the M dwarf radius valley

Van Eylen,

Astudillo-Defru,

Bonfils

et al. 2021

Preprint

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We report on precise Doppler measurements of L231-32 (TOI-270), a nearby M dwarf (𝑑 = 22 pc, 𝑀 ★ = 0.39 M , 𝑅 ★ = 0.38 R ), which hosts three transiting planets that were recently discovered using data from the Transiting Exoplanet Survey Satellite (TESS). The three planets are 1.1, 2.3, and 2.0 times the size of Earth and have orbital periods of 3.4, 5.7, and 11.4 days. We obtained 29 high-resolution optical spectra with the newly commissioned Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) and 58 spectra using the High Accuracy Radial velocity Planet Searcher (HARPS). From these observations, we find the masses of the planets to be 1.58±0.26, 6.14±0.38, and 4.78±0.46 M ⊕ , respectively. The combination of radius and mass measurements suggests that the innermost planet has a rocky composition similar to that of Earth, while the outer two planets have lower densities. Thus, the inner planet and the outer planets are on opposite sides of the 'radius valley' -a region in the radius-period diagram with relatively few members, which has been interpreted as a consequence of atmospheric photo-evaporation. We place these findings into the context of other small close-in planets orbiting M dwarf stars, and use support vector machines to determine the location and slope of the M dwarf (𝑇 eff < 4000 K) radius valley as a function of orbital period. We compare the location of the M dwarf radius valley to the radius valley observed for FGK stars, and find that its location is a good match to photo-evaporation and core-powered mass loss models. Finally, we show that planets below the M dwarf radius valley have compositions consistent with stripped rocky cores, whereas most planets above have a lower density consistent with the presence of a H-He atmosphere.

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Section: Expected Location Of the M Dwarf Radius Valleymentioning

confidence: 99%

Masses and compositions of three small planets orbiting the nearby M dwarf L231-32 (TOI-270) and the M dwarf radius valley

Van Eylen,

Astudillo-Defru,

Bonfils

et al. 2021

Preprint

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“…Further details on this procedure can be found in Ramírez et al (2014b). For this analysis we employed the Kurucz (ATLAS9) grid of model atmospheres (Castelli & Kurucz 2004) and we assumed the following solar parameters: T eff =5777 K, log g=4.44 dex, [Fe/H]=0.00 dex and ξ =1.00 km s −1 (e.g., Cox 2000). The errors associated with the stellar parameters are evaluated by the code following the procedure described in Epstein et al (2010) and Bensby et al (2014), that takes into account the dependence between the parameters in the fulfilment of the three equilibrium conditions.…”

Section: Stellar Parameters and Abundancesmentioning

confidence: 99%

The temporal evolution of neutron-capture elements in the Galactic discs

Spina

Meléndez

Karakas

et al. 2017

Monthly Notices of the Royal Astronomical Society

110

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Important insights into the formation and evolution of the Galactic disc(s) are contained in the chemical compositions of stars. We analysed high-resolution and high signal to noise HARPS spectra of 79 solar twin stars in order to obtain precise determinations of their atmospheric parameters, ages (σ∼0.4 Gyr) and chemical abundances (σ<0.01 dex) of 12 neutron-capture elements (Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, and Dy). This valuable dataset allows us to study the [X/Fe]-age relations over a time interval of ∼10 Gyr and among stars belonging to the thin and thick discs. These relations show that i) the s-process has been the main channel of nucleosynthesis of n-capture elements during the evolution of the thin disc; ii) the thick disc is rich in r-process elements which suggests that its formation has been rapid and intensive. In addition, the heavy (Ba, La, Ce) and light (Sr, Y, Zr) s-process elements revealed details on the dependence between the yields of AGB stars and the stellar mass or metallicity. Finally, we confirmed that both [Y/Mg] and [Y/Al] ratios can be employed as stellar clocks, allowing ages of solar twin stars to be estimated with an average precision of ∼0.5 Gyr.

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“…Throughout our differential analysis we have also adopted the standard parameters for the Sun: T eff = 5777 K, log g = 4.44, [Fe/H] = 0.00 dex and ξ = 1.00 km s −1 (e.g. (Cox 2000)). The solar chemical composition by Asplund et al (2009), and by Grevesse et al (2015) specifically for the heavy elements Cu to Th, have been adopted as reference, such that the adopted Sun's Th abundance is log (Th)=0.03 dex.…”

Section: Homogeneous Thorium Abundancesmentioning

confidence: 99%

Thorium in solar twins: implications for habitability in rocky planets

Botelho

Milone

Meléndez

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We have investigated the thorium (Th) abundance in a sample of 53 thin disc solar twins covering a wide range of ages. These data provide constrains on the mantle energy budget of terrestrial planets that can be formed over the evolution of the Galaxy's thin disc. We have estimated Th abundances with an average precision of 0.025 dex (in both [Th/H] and [Th/Fe]) through comprehensive spectral synthesis of a Th II line present at 4019.1290Å, using very high resolution (R = 115,000) high quality HARPS spectra obtained at the ESO La Silla Observatory. We have confirmed that there is a large energy budget from Th decay for maintaining mantle convection inside potential rocky planets around solar twins, from the Galactic thin disc formation until now, because the pristine [Th/H] ZAMS is super-solar on average under a uniform dispersion of 0.056 dex (varying from +0.037 up to +0.138 dex based on linear fits against isochrone stellar age). Comparing to neodymium (Nd) and europium (Eu), two others neutron-capture elements, the stellar pristine abundance of Th follows Eu along the Galactic thin disc evolution, but it does not follow Nd, probably because neodymium has a significant contribution from the s-process (about 60 per cent).

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Introduction

Cited by 3 publications

References 0 publications

Masses and compositions of three small planets orbiting the nearby M dwarf L231-32 (TOI-270) and the M dwarf radius valley

Masses and compositions of three small planets orbiting the nearby M dwarf L231-32 (TOI-270) and the M dwarf radius valley

The temporal evolution of neutron-capture elements in the Galactic discs

Thorium in solar twins: implications for habitability in rocky planets

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