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The EBLM project - VIII. First results for M-dwarf mass, radius, and effective temperature measurements using CHEOPS light curves

M. I. Swayne, P. F. L. Maxted, A. H. M. J. Triaud, S. G. Sousa, C. Broeg, H. -. Florén, P. Guterman, A. E. Simon, I. Boisse, A. Bonfanti, D. Martin, A. Santerne, S. Salmon, M. R. Standing, V. Van Grootel, T. G. Wilson, Y. Alibert, R. Alonso, G. Anglada Escudé, J. Asquier, T. Bárczy, D. Barrado, S. C. C. Barros, M. Battley, W. Baumjohann, M. Beck, T. Beck, A. Bekkelien, W. Benz, N. Billot, X. Bonfils, A. Brandeker, M. -D. Busch, J. Cabrera, S. Charnoz, A. Collier Cameron, Sz. Csizmadia, M. B. Davies, M. Deleuil, A. Deline, L. Delrez, O. Demangeon, B.-O. Demory, G. Dransfield, D. Ehrenreich, A. Erikson, A. Fortier, L. Fossati, M. Fridlund, D. Futyan, D. Gandolfi, M. Gillon, M. Guedel, G. Hébrard, N. Heidari, C. Hellier, K. Heng, M. Hobson, S. Hoyer, K. Isaak, L. L. Kiss, V. Kunovac Hod¸ić, S. Lalitha, J. Laskar, A. Lecavelier Des Etangs, M. Lendl, C. Lovis, D. Magrin, L. Marafatto, J. McCormac, N. Miller, V. Nascimbeni, G. Olofsson, R. Ottensamer, I. Pagano, E. Pallé, G. Peter, G. Piotto, D. Pollacco, D. Queloz, R. Ragazzoni, N. Rando, H. Rauer, I. Ribas, N. C. Santos, G. Scandariato, D. Ségransan, A. M. S. Smith, M. Steinberger, M. Steller, Gy. M. Szabó, N. Thomas, S. Udry, I. Walter, N. A. Walton, E. Willett

Abstract
The accuracy of theoretical mass, radius, and effective temperature values for M-dwarf stars is an active topic of debate. Differences between observed and theoretical values have raised the possibility that current theoretical stellar structure and evolution models are inaccurate towards the low-mass end of the main sequence. To explore this issue, we use the CHEOPS satellite to obtain high-precision light curves of eclipsing binaries with low-mass stellar companions. We use these light curves combined with the spectroscopic orbit for the solar-type companion to measure the mass, radius, and effective temperature of the M-dwarf star. Here, we present the analysis of three eclipsing binaries. We use the pycheops data analysis software to fit the observed transit and eclipse events of each system. Two of our systems were also observed by the TESS satellite – we similarly analyse these light curves for comparison. We find consistent results between CHEOPS and TESS, presenting three stellar radii and two stellar effective temperature values of low-mass stellar objects. These initial results from our on-going observing programme with CHEOPS show that we can expect to have ∼24 new mass, radius, and effective temperature measurements for very low-mass stars within the next few years.

Keywords
techniques: photometric, techniques: spectroscopic, binaries: eclipsing, stars: fundamental parameters, stars: low-mass

Monthly Notices of the Royal Astronomical Society
Volume 506, Issue 1, Page 306
2021 September

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia