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The scatter of the M dwarf mass-radius relationship

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posted on 04.02.2019, 12:18 by S. G. Parsons, B. T. Gansicke, T. R. Marsh, R. P. Ashley, E. Breedt, M. R. Burleigh, C. M. Copperwheat, V. S. Dhillon, M. J. Green, J. J. Hermes, P. Irawati, P. Kerry, S. P. Littlefair, A. Rebassa-Mansergas, D. I. Sahman, M. R. Schreiber, M. Zorotovic
M dwarfs are prime targets in the hunt for habitable worlds around other stars. This is due to their abundance as well as their small radii and low masses and temperatures, which facilitate the detection of temperate, rocky planets in orbit around them. However, the fundamental properties of M dwarfs are difficult to constrain, often limiting our ability to characterize the planets they host. Here we test several theoretical relationships for M dwarfs by measuring 23 high-precision, model-independent masses and radii for M dwarfs in binaries with white dwarfs. We find a large scatter in the radii of these low-mass stars, with 25 per cent having radii consistent with theoretical models while the rest are up to 12 per cent overinflated. This scatter is seen in both partially and fully convective M dwarfs. No clear trend is seen between the overinflation and age or metallicity, but there are indications that the radii of slowly rotating M dwarfs are more consistent with predictions, albeit with a similar amount of scatter in the measurements compared to more rapidly rotating M dwarfs. The sample of M dwarfs in close binaries with white dwarfs appears indistinguishable from other M dwarf samples, implying that common envelope evolution has a negligible impact on their structure. We conclude that theoretical and empirical mass–radius relationships lack the precision and accuracy required to measure the fundamental parameters of M dwarfs well enough to determine the internal structure and bulk composition of the planets they host.


SGP acknowledges the support of the Leverhulme Trust. The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement numbers 340040 (HiPERCAM) and 320964 (WDTracer). ULTRACAM, TRM, VSD, and SPL are supported by the Science and Technology Facilities Council (STFC). ARM acknowledges financial support from the MINECO Ramón y Cajal programme RYC-2016-20254 and the grant AYA2017-86274-P, and from the AGAUR(SGR-661/2017). Support for this work was provided by NASA through Hubble Fellowship grant HST-HF2-51357.001-A. MRS thanks for support from FONDECYT (1141269) and Millennium Science Initiative, Chilean ministry of Economy: Nucleus P10-022-F. MZ acknowledges support from CONICYT PAI (Concurso Nacional de Inserción en la Academia 2017, Folio 79170121) and CONICYT/FONDECYT (Programa de Iniciación, Folio 11170559). This work has made use of data obtained at the Thai National Observatory on Doi Inthanon, operated by NARIT. The results presented in this paper are based on observations collected at the European Southern Observatory under programme IDs 086.D-0161,086.D-0265, 192.D-0270 and 099.D-0252.



Monthly Notices of the Royal Astronomical Society, 2018, 481 (1), pp. 1083-1096 (14)

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Monthly Notices of the Royal Astronomical Society


Oxford University Press (OUP), Royal Astronomical Society





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