Discovery of two warm mini-Neptunes with contrasting densities orbiting the young K3V star TOI-815
Journal article, 2024
We present the discovery and characterization of two warm mini-Neptunes transiting the K3V star TOI-815 in a K–M binary system. Analysis of its spectra and rotation period reveal the star to be young, with an age of 200+−400200 Myr. TOI-815b has a 11.2-day period and a radius of 2.94 ± 0.05 R+ with transits observed by TESS, CHEOPS, ASTEP, and LCOGT. The outer planet, TOI-815c, has a radius of 2.62 ± 0.10 R+, based on observations of three nonconsecutive transits with TESS; targeted CHEOPS photometry and radial velocity follow-up with ESPRESSO were required to confirm the 35-day period. ESPRESSO confirmed the planetary nature of both planets and measured masses of 7.6 ± 1.5 M+ (ρP = 1.64+−003331 g cm−3) and 23.5 ± 2.4 M+ (ρP = 7.2+−1110 g cm−3), respectively. Thus, the planets have very different masses, which is unusual for compact multi-planet systems. Moreover, our statistical analysis of mini-Neptunes orbiting FGK stars suggests that weakly irradiated planets tend to have higher bulk densities compared to those undergoing strong irradiation. This could be ascribed to their cooler atmospheres, which are more compressed and denser. Internal structure modeling of TOI-815b suggests it likely has a H-He atmosphere that constitutes a few percent of the total planet mass, or higher if the planet is assumed to have no water. In contrast, the measured mass and radius of TOI-815c can be explained without invoking any atmosphere, challenging planetary formation theories. Finally, we infer from our measurements that the star is viewed close to pole-on, which implies a spin-orbit misalignment at the 3σ level. This emphasizes the peculiarity of the system’s orbital architecture, and probably hints at an eventful dynamical history.
techniques: radial velocities
techniques: photometric
planets and satellites: composition
stars: individual: TOI-815
planets and satellites: detection
planets and satellites: formation
Author
A. Psaridi
University of Geneva
H. P. Osborn
University of Bern
F. Bouchy
University of Geneva
M. Lendl
University of Geneva
Léna Parc
University of Geneva
N. Billot
University of Geneva
C. Broeg
University of Bern
S.G. Sousa
University of Porto
V. Adibekyan
University of Porto
Omar Attia
University of Geneva
A. Bonfanti
Institut fur Weltraumforschung
Hritam Chakraborty
University of Geneva
Karen A. Collins
Harvard-Smithsonian Center for Astrophysics
Jeanne Davoult
University of Bern
E. Delgado Mena
University of Porto
N. Grieves
University of Geneva
T. Guillot
Observatoire de la Cote d'Azur
A. Heitzmann
University of Geneva
R. Helled
University of Zürich
Coel Hellier
Keele University
Jon M. Jenkins
NASA Ames Research Center
Henrik Knierim
University of Zürich
A. Krenn
Institut fur Weltraumforschung
Jack J. Lissauer
NASA Ames Research Center
R. Luque
University of Chicago
D. Rapetti
NASA Ames Research Center
N. C. Santos
University of Porto
Olga Suárez
Observatoire de la Cote d'Azur
J. Venturini
University of Geneva
Francis P. Wilkin
Union College
T.G. Wilson
The University of Warwick
J. N. Winn
Princeton University
C. Ziegler
Stephen F. Austin State University
Tiziano Zingales
University of Padua
Y. Alibert
University of Bern
A. Brandeker
Stockholm University
J. A. Egger
University of Bern
D. Gandolfi
University of Turin
M.J. Hooton
University of Cambridge
A. Tuson
University of Cambridge
S. Ulmer-Moll
University of Geneva
L. Abe
Observatoire de la Cote d'Azur
R. Allart
Université de Montréal
R. Alonso
Instituto de Astrofísica de Canarias
D. Anderson
The University of Warwick
G. A. Escudé
Institute of Space Sciences (ICE) - CSIC
T. Bárczy
Admatis
D. Barrado
Centro de Astrobiologia (CAB)
S.C.C. Barros
University of Porto
W. Baumjohann
Institut fur Weltraumforschung
M. Beck
University of Geneva
T. Beck
University of Bern
W. Benz
University of Bern
X. Bonfils
Institut de Planétologie et d’Astrophysique de Grenoble (IPAG)
L. Borsato
Istituto nazionale di astrofisica (INAF)
V. Bourrier
University of Geneva
D. R. Ciardi
California Institute of Technology (Caltech)
A. Collier Cameron
University of St Andrews
S. Charnoz
Institut de Physique du Globe de Paris
M. Cointepas
University of Geneva
Szilard Csizmadia
German Aerospace Center (DLR)
P. E. Cubillos
Institut fur Weltraumforschung
G. Lo Curto
European Southern Observatory Santiago
M. B. Davies
Lund University
Tansu Daylan
Washington University in St. Louis
M. Deleuil
Laboratoire d'Astrophysique de Marseille
A. Deline
University of Geneva
L. Delrez
University of Liège
O. Demangeon
University of Porto
B.O. Demory
University of Bern
C. Dorn
Swiss Federal Institute of Technology in Zürich (ETH)
X. Dumusque
University of Geneva
D. Ehrenreich
University of Geneva
Anders Erikson
German Aerospace Center (DLR)
A. L. des Etangs
Institut d 'Astrophysique de Paris
D. de Miguel
Airbus Group
A. Fortier
University of Bern
L. Fossati
Institut fur Weltraumforschung
Yolanda G.C. Frensch
University of Geneva
Malcolm Fridlund
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Leiden University
Michaël Gillon
University of Liège
M. Gudel
University of Vienna
Maximilian N. Günther
European Space Research and Technology Centre (ESA ESTEC)
J. Hagelberg
University of Geneva
Ch. Helling
Institut fur Weltraumforschung
S. Hoyer
Laboratoire d'Astrophysique de Marseille
K. Isaak
European Space Research and Technology Centre (ESA ESTEC)
L. L. Kiss
Hungarian Academy of Sciences
K. W.F. Lam
German Aerospace Center (DLR)
J. Laskar
Paris Observatory
B. Lavie
University of Geneva
C. Lovis
University of Geneva
D. Magrin
Istituto nazionale di astrofisica (INAF)
L. Marafatto
Istituto nazionale di astrofisica (INAF)
P. Maxted
Keele University
S. McDermott
Protologic LLC
Djamel Mékarnia
Observatoire de la Cote d'Azur
C. Mordasini
University of Bern
F. Murgas
University of La Laguna
Valerio Nascimbeni
Istituto nazionale di astrofisica (INAF)
L. D. Nielsen
European Southern Observatory (ESO)
G. Olofsson
Stockholm University
R. Ottensamer
University of Vienna
I. Pagano
Istituto nazionale di astrofisica (INAF)
Enric Palle
Instituto de Astrofísica de Canarias
G. Peter
German Aerospace Center (DLR)
Giampaolo P. Piotto
University of Padua
Don L. Pollacco
The University of Warwick
D. Queloz
University of Cambridge
Roberto Ragazzoni
University of Padua
Devin Ramos
Union College
N. Rando
European Space Research and Technology Centre (ESA ESTEC)
H. Rauer
German Aerospace Center (DLR)
C. Reimers
University of Vienna
I. Ribas
Institute of Space Sciences (ICE) - CSIC
S. Seager
Massachusetts Institute of Technology (MIT)
D. Segransan
University of Geneva
Gaetano Scandariato
Istituto nazionale di astrofisica (INAF)
A.E. Simon
University of Bern
A. M.S. Smith
German Aerospace Center (DLR)
M. Stalport
University of Liège
Manfred B. Steller
Institut fur Weltraumforschung
G.M. Szabó
Eötvös Loránd University (ELTE)
Nicolas Thomas
University of Bern
T. Pritchard
NASA Goddard Space Flight Center
S. Udry
University of Geneva
C. Corral Van Damme
European Space Research and Technology Centre (ESA ESTEC)
V. Van Grootel
University of Liège
E. Villaver
Instituto de Astrofísica de Canarias
I. Walter
German Aerospace Center (DLR)
N. A. Walton
University of Cambridge
Cristilyn N. Watkins
Harvard-Smithsonian Center for Astrophysics
Richard G West
The University of Warwick
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 685 A5Subject Categories
Meteorology and Atmospheric Sciences
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/202348678