Investigating the architecture and internal structure of the TOI-561 system planets with CHEOPS, HARPS-N and TESS

We present a precise characterization of the TOI-561 planetary system obtained by combining previously published data with TESS and CHEOPS photometry,and a new set of 62 HARPS-N radial velocities (RVs). Our joint analysis confirms the presence of four transiting planets, namely TOI-561 b (P =0.45 d, R = 1.42 R⊕, M =2.0 M⊕), c (P = 10.78 d, R =2.91 R⊕, M = 5.4 M⊕),d (P = 25.7 d, R = 2.82 R⊕, M =13.2 M⊕) and e (P = 77 d, R =2.55 R⊕, M = 12.6 R⊕).Moreover, we identify an additional, long-period signal (>450 d) in theRVs, which could be due to either an external planetary companion or to stellar magnetic activity. The precise masses and radii obtained for the four planetsallowed us to conduct interior structure and atmospheric escape modelling. TOI-561b is confirmed to be the lowest density (ρb = 3.8 ± 0.5 gcm−3) ultra-short period (USP) planet known to date, and the low metallicity of the host star makes it consistent with the general bulk density-stellar metallicity trend. According to our interior structure modelling, planet b has basically no gas envelope, and it could host a certainamount of water. In contrast, TOI-561 c, d, and e likely retained an H/Heenvelope, in addition to a possibly large water layer. The inferred planetary compositions suggest different atmospheric evolutionary paths, with planets band c having experienced significant gas loss, and planets d and e showing anatmospheric content consistent with the original one. The uniqueness of the USPplanet, the presence of the long-period planet TOI-561 e, and the complex architecture make this system an appealing target for follow-up studies.

Citation

Lacedelli , G , Wilson , T G , Malavolta , L , Hooton , M J , Cameron , A C , Alibert , Y , Mortier , A , Bonfanti , A , Haywood , R D , Hoyer , S , Piotto , G , Bekkelien , A , Vanderburg , A M , Benz , W , Dumusque , X , Deline , A , López-Morales , M , Borsato , L , Rice , K , Fossati , L , Latham , D W , Brandeker , A , Poretti , E , Sousa , S G , Sozzetti , A , Salmon , S , Burke , C J , Van Grootel , V , Fausnaugh , M M , Adibekyan , V , Huang , C X , Osborn , H P , Mustill , A J , Pallé , E , Bourrier , V , Nascimbeni , V , Alonso , R , Anglada , G , Bárczy , T , Navascues , D B Y , Barros , S C C , Baumjohann , W , Beck , M , Beck , T , Billot , N , Bonfils , X , Broeg , C , Buchhave , L A , Cabrera , J , Charnoz , S , Cosentino , R , Csizmadia , S , Davies , M B , Deleuil , M , Delrez , L , Demangeon , O , Demory , B-O , Ehrenreich , D , Erikson , A , Esparza-Borges , E , Florén , H-G , Fortier , A , Fridlund , M , Futyan , D , Gandolfi , D , Ghedina , A , Gillon , M , Güdel , M , Gutermann , P , Harutyunyan , A , Heng , K , Isaak , K G , Jenkins , J M , Kiss , L , Laskar , J , Lecavelier des Etangs , A , Lendl , M , Lovis , C , Magrin , D , Marafatto , L , Martinez Fiorenzano , A F , Maxted , P F L , Mayor , M , Micela , G , Molinari , E , Murgas , F , Narita , N , Olofsson , G , Ottensamer , R , Pagano , I , Pasetti , A , Pedani , M , Pepe , F A , Peter , G , Phillips , D F , Pollacco , D , Queloz , D , Ragazzoni , R , Rando , N , Ratti , F , Rauer , H , Ribas , I , Santos , N C , Sasselov , D , Scandariato , G , Seager , S , Ségransan , D , Serrano , L M , Simon , A E , Smith , A M S , Steinberger , M , Steller , M , Szabó , G , Thomas , N , Twicken , J D , Udry , S , Walton , N & Winn , J N 2022 , ' Investigating the architecture and internal structure of the TOI-561 system planets with CHEOPS, HARPS-N and TESS ' , Monthly Notices of the Royal Astronomical Society , vol. Advance Article . https://doi.org/10.1093/mnras/stac199

Publication

Monthly Notices of the Royal Astronomical Society

Status

Peer reviewed

DOI

https://doi.org/10.1093/mnras/stac199

ISSN

0035-8711

Type

Journal article

Rights

Copyright © 2022 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This work has been made available online in accordance with publisher policies or with permission. Permission for further reuse of this content should be sought from the publisher or the rights holder. This is the author created accepted manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1093/mnras/stac199.

Description

Funding: TW and ACC acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1.

Collections

University of St Andrews Research

URI

http://hdl.handle.net/10023/24936