CHEOPS observations of the HD 108236 planetary system: A fifth planet, improved ephemerides, and planetary radii
Journal article, 2021
Context. The detection of a super-Earth and three mini-Neptunes transiting the bright (V = 9.2 mag) star HD 108236 (also known as TOI-1233) was recently reported on the basis of TESS and ground-based light curves. Aims. We perform a first characterisation of the HD 108236 planetary system through high-precision CHEOPS photometry and improve the transit ephemerides and system parameters. Methods. We characterise the host star through spectroscopic analysis and derive the radius with the infrared flux method. We constrain the stellar mass and age by combining the results obtained from two sets of stellar evolutionary tracks. We analyse the available TESS light curves and one CHEOPS transit light curve for each known planet in the system. Results. We find that HD 108236 is a Sun-like star with R? = 0.877 ± 0.008 R? , M? = 0.869-0.048+0.050 M? , and an age of 6.7-5.1+4.0 Gyr. We report the serendipitous detection of an additional planet, HD 108236 f, in one of the CHEOPS light curves. For this planet, the combined analysis of the TESS and CHEOPS light curves leads to a tentative orbital period of about 29.5 days. From the light curve analysis, we obtain radii of 1.615 ± 0.051, 2.071 ± 0.052, 2.539-0.065+0.062, 3.083 ± 0.052, and 2.017-0.057+0.052 R? for planets HD 108236 b to HD 108236 f, respectively. These values are in agreement with previous TESS-based estimates, but with an improved precision of about a factor of two. We perform a stability analysis of the system, concluding that the planetary orbits most likely have eccentricities smaller than 0.1. We also employ a planetary atmospheric evolution framework to constrain the masses of the five planets, concluding that HD 108236 b and HD 108236 c should have an Earth-like density, while the outer planets should host a low mean molecular weight envelope. Conclusions. The detection of the fifth planet makes HD 108236 the third system brighter than V = 10 mag to host more than four transiting planets. The longer time span enables us to significantly improve the orbital ephemerides such that the uncertainty on the transit times will be of the order of minutes for the years to come. A comparison of the results obtained from the TESS and CHEOPS light curves indicates that for a V - 9 mag solar-like star and a transit signal of -500 ppm, one CHEOPS transit light curve ensures the same level of photometric precision as eight TESS transits combined, although this conclusion depends on the length and position of the gaps in the light curve.
Ephemerides
Planets and satellites: Fundamental parameters
Planets and satellites: Detection
Stars: Fundamental parameters
Author
A. Bonfanti
Institut fur Weltraumforschung
L. Delrez
University of Liège
M.J. Hooton
University of Bern
T.G. Wilson
University of St Andrews
L. Fossati
Institut fur Weltraumforschung
Y. Alibert
University of Bern
S. Hoyer
Laboratoire d'Astrophysique de Marseille
A. J. Mustill
Lund University
H. P. Osborn
University of Bern
V. Adibekyan
University of Porto
D. Gandolfi
Istituto nazionale di astrofisica (INAF)
S. Salmon
University of Liège
S.G. Sousa
University of Porto
A. Tuson
University of Cambridge
V. Van Grootel
University of Liège
J. Cabrera
German Aerospace Center (DLR)
Valerio Nascimbeni
Istituto nazionale di astrofisica (INAF)
P. Maxted
Keele University
S.C.C. Barros
University of Porto
N. Billot
University of Geneva
X. Bonfils
Grenoble Alpes University
L. Borsato
Istituto nazionale di astrofisica (INAF)
C. Broeg
University of Bern
Melvyn B. Davies
Lund University
M. Deleuil
Laboratoire d'Astrophysique de Marseille
O. Demangeon
Laboratoire d'Astrophysique de Marseille
Malcolm Fridlund
Leiden University
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
G. Lacedelli
Istituto nazionale di astrofisica (INAF)
M. Lendl
University of Geneva
C. M. Persson
N. C. Santos
University of Porto
Gaetano Scandariato
Istituto nazionale di astrofisica (INAF)
G.M. Szabó
Eötvös Loránd University (ELTE)
A. Collier Cameron
University of St Andrews
S. Udry
University of Geneva
W. Benz
University of Bern
M. Beck
University of Geneva
D. Ehrenreich
University of Geneva
A. Fortier
University of Bern
K. Isaak
European Space Agency (ESA)
D. Queloz
University of Geneva
R. Alonso
Instituto de Astrofísica de Canarias
J. Asquier
European Space Agency (ESA)
T. Bandy
University of Bern
T. Bárczy
Admatis
D. Barrado
Centro de Astrobiologia (CAB)
O. Barragán
University of Oxford
W. Baumjohann
Institut fur Weltraumforschung
T. Beck
University of Bern
A. Bekkelien
University of Geneva
M. Bergomi
Istituto nazionale di astrofisica (INAF)
A. Brandeker
Stockholm University
M.-D. Busch
University of Bern
V. Cessa
University of Bern
S. Charnoz
Institut de Physique du Globe de Paris
B. Chazelas
University of Geneva
C. Corral Van Damme
European Space Agency (ESA)
B.O. Demory
University of Bern
Anders Erikson
German Aerospace Center (DLR)
J. Farinato
Istituto nazionale di astrofisica (INAF)
D. Futyan
University of Geneva
A. Garcia Munoz
Technische Universität Berlin
Michaël Gillon
University of Liège
M. Guedel
University of Vienna
P. Guterman
Laboratoire d'Astrophysique de Marseille
J. Hasiba
Institut fur Weltraumforschung
Kevin Heng
University of Bern
E. Hernandez
University of Bern
L. Kiss
Hungarian Academy of Sciences
T. Kuntzer
University of Geneva
J. Laskar
Paris Observatory
A. L. des Etangs
Institut d 'Astrophysique de Paris
C. Lovis
University of Geneva
D. Magrin
Istituto nazionale di astrofisica (INAF)
L. Malvasio
University of Bern
L. Marafatto
Istituto nazionale di astrofisica (INAF)
H. Michaelis
German Aerospace Center (DLR)
M. Munari
Istituto nazionale di astrofisica (INAF)
G. Olofsson
Stockholm University
H. Ottacher
Institut fur Weltraumforschung
R. Ottensamer
University of Vienna
I. Pagano
Istituto nazionale di astrofisica (INAF)
E. Palle
Instituto de Astrofísica de Canarias
G. Peter
German Aerospace Center (DLR)
D. Piazza
University of Bern
Giampaolo P. Piotto
Istituto nazionale di astrofisica (INAF)
Don L. Pollacco
The University of Warwick
Roberto Ragazzoni
Istituto nazionale di astrofisica (INAF)
N. Rando
European Space Agency (ESA)
F. Ratti
European Space Agency (ESA)
H. Rauer
German Aerospace Center (DLR)
I. Ribas
Spanish National Research Council (CSIC)
M. Rieder
University of Bern
R. Rohlfs
University of Geneva
F. Safa
European Space Agency (ESA)
M. Salatti
Agenzia Spaziale Italiana
D. Segransan
University of Geneva
A.E. Simon
University of Bern
Alexis M. S. Smith
German Aerospace Center (DLR)
M. Sordet
University of Geneva
Manfred B. Steller
Institut fur Weltraumforschung
Nicolas Thomas
University of Bern
M. Tschentscher
German Aerospace Center (DLR)
Vincent Van Eylen
University College London (UCL)
V. Viotto
Istituto nazionale di astrofisica (INAF)
I. Walter
German Aerospace Center (DLR)
N. A. Walton
University of Cambridge
F. Wildi
University of Geneva
D. Wolter
German Aerospace Center (DLR)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 646 A157Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
Atom and Molecular Physics and Optics
Control Engineering
DOI
10.1051/0004-6361/202039608