An unusually low density ultra-short period super-Earth and three mini-Neptunes around the old star TOI-561
Abstract
Based on HARPS-N radial velocities (RVs) and TESS photometry, we present a full characterisation of the planetary system orbiting the late G dwarf After the identification of three transiting candidates by TESS, we discovered two additional external planets from RV analysis. RVs cannot confirm the outer TESS transiting candidate, which would also make the system dynamically unstable. We demonstrate that the two transits initially associated with this candidate are instead due to single transits of the two planets discovered using RVs. The four planets orbiting TOI-561 include an ultra-short period (USP) super-Earth (TOI-561 b) with period Pb = 0.45 d, mass Mb = 1.59 ± 0.36 M⊕ and radius Rb = 1.42 ± 0.07 R⊕, and three mini-Neptunes: TOI-561 c, with Pc = 10.78 d, Mc = 5.40 ± 0.98 M⊕, Rc = 2.88 ± 0.09 R⊕; TOI-561 d, with Pd = 25.6 d, Md = 11.9 ± 1.3 M⊕, Rd = 2.53 ± 0.13 R⊕; and TOI-561 e, with Pe = 77.2 d, Me = 16.0 ± 2.3 M⊕, Re = 2.67 ± 0.11 R⊕. Having a density of 3.0 ± 0.8 g cm−3, TOI-561 b is the lowest density USP planet known to date. Our N-body simulations confirm the stability of the system and predict a strong, anti-correlated, long-term transit time variation signal between planets d and e. The unusual density of the inner super-Earth and the dynamical interactions between the outer planets make TOI-561 an interesting follow-up target.
Citation
Lacedelli , G , Malavolta , L , Borsato , L , Piotto , G , Nardiello , D , Mortier , A , Stalport , M , Cameron , A C , Poretti , E , Buchhave , L A , López-Morales , M , Nascimbeni , V , Wilson , T G , Udry , S , Latham , D W , Bonomo , A S , Damasso , M , Dumusque , X , Jenkins , J M , Lovis , C , Rice , K , Sasselov , D , Winn , J N , Andreuzzi , G , Cosentino , R , Charbonneau , D , Di Fabrizio , L , Martinez Fiorenzano , A F , Ghedina , A , Harutyunyan , A , Lienhard , F , Micela , G , Molinari , E , Pagano , I , Pepe , F , Phillips , D F , Pinamonti , M , Ricker , G , Scandariato , G , Sozzetti , A & Watson , C A 2021 , ' An unusually low density ultra-short period super-Earth and three mini-Neptunes around the old star TOI-561 ' , Monthly Notices of the Royal Astronomical Society , vol. 501 , no. 3 , pp. 4148–4166 . https://doi.org/10.1093/mnras/staa3728
Publication
Monthly Notices of the Royal Astronomical Society
Status
Peer reviewed
ISSN
0035-8711Type
Journal article
Description
Funding: GL acknowledges support by CARIPARO Foundation, according to the agreement CARIPARO-Universit`a degli Studidi Padova (Pratica n. 2018/0098), and scholarship support by the “Soroptimist International d’Italia” association (Cortina d’Ampezzo Club). GLa, LBo, GPi, VN, GS, and IPa acknowledge the funding support from Italian Space Agency (ASI) regulated by “Accordo ASI-INAF n. 2013-016-R.0 del 9 luglio 2013 e integrazione del 9 luglio 2015 CHEOPS Fasi A/B/C”. DNa acknowledges the support from the French Centre National d’Etudes Spatiales (CNES). AM acknowledges support from the senior Kavli Institute Fellowships. ACC acknowledges support from STFC consolidated grant ST/R000824/1 and UK Space Agency grant ST/R003203/1. ASB and MPi acknowledge financial contribution from the ASI-INAF agreement n.2018-16-HH.0. XD is grateful to the Branco-Weiss Fellowship for continuous support.This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No. 851555). JNW thanks the Heising-Simons Foundation for support).Collections
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