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TOI-269 b: an eccentric sub-Neptune transiting a M2 dwarf revisited with ExTrA

M. Cointepas, J.-M. Almenara, X. Bonfils, F. Bouchy, N. Astudillo-Defru, F. Murgas, J. F. Otegi, A. Wyttenbach, D. R. Anderson, E. Artigau, B. L. Canto Martins, D. Charbonneau, K. A. Collins, K. I. Collins, J. Correia, S. Curaba, A. Delboulbé, X. Delfosse, R. F. Díaz, C. Dorn, R. Doyon, P. Feautrier, P. Figueira, T. Forveille, G. Gaisne, T. Gan, L. Gluck, R. Helled, C. Hellier, L. Jocou, P. Kern, S. Lafrasse, N. M. Law, I. C. Leão, C. Lovis, Y. Magnard, A. W. Mann, D. Maurel, J. R. de Medeiros, C. Melo, T. Moulin, F. Pepe, P. Rabou, S. Rochat, D. R. Rodriguez, A. Roux, N. C. Santos, D. Ségransan, E. Stadler, E. B. Ting, J. D. Twicken, S. Udry, W. C. Waalkes, R. G. West, A. Wünsche, C. Ziegler, G. R. Ricker, R. K. Vanderspek, D. W. Latham, S. Seager, J. N. Winn, J. M. Jenkins

Abstract
We present the confirmation of a new sub-Neptune close to the transition between super-Earths and sub-Neptunes transiting the M2 dwarf TOI-269 (TIC 220 479 565, V = 14.4 mag, J = 10.9 mag, R = 0.40 R, M = 0.39 M, d = 57 pc). The exoplanet candidate has been identified in multiple TESS sectors, and validated with high-precision spectroscopy from HARPS and ground-based photometric follow-up from ExTrA and LCO-CTIO. We determined mass, radius, and bulk density of the exoplanet by jointly modeling both photometry and radial velocities with juliet. The transiting exoplanet has an orbital period of P = 3.6977104 ± 0.0000037 days, a radius of 2.77 ± 0.12 R, and a mass of 8.8 ± 1.4 M. Since TOI-269 b lies among the best targets of its category for atmospheric characterization, it would be interesting to probe the atmosphere of this exoplanet with transmission spectroscopy in order to compare it to other sub-Neptunes. With an eccentricity e = 0.425−0.086+0.082, TOI-269 b has one of the highest eccentricities of the exoplanets with periods less than 10 days. The star being likely a few Gyr old, this system does not appear to be dynamically young. We surmise TOI-269 b may have acquired its high eccentricity as it migrated inward through planet-planet interactions.

Keywords
planets and satellites: detection; stars: low-mass; techniques: photometric; techniques: radial velocities; Astrophysics - Earth and Planetary Astrophysics

Notes
ExTrA photometric data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/650/A145

Astronomy & Astrophysics
Volume 650, Article Number A145, Number of pages 18
2021 June

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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