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.

Planets and satellites: Fundamental parameters

Ephemerides

Stars: Fundamental parameters

Planets and satellites: Detection

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

Osservatorio Astronomico di Padova

P. Maxted

Keele University

S.C.C. Barros

University of Porto

N. Billot

University of Geneva

X. Bonfils

Grenoble Alpes University

L. Borsato

Osservatorio Astronomico di Padova

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

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

Leiden University

G. Lacedelli

Osservatorio Astronomico di Padova

M. Lendl

University of Geneva

C. M. Persson

N. C. Santos

University of Porto

Gaetano Scandariato

Osservatorio Astrofisico di Catania

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 Research and Technology Centre (ESA ESTEC)

D. Queloz

University of Geneva

R. Alonso

Instituto Astrofisico de Canarias

J. Asquier

European Space Research and Technology Centre (ESA ESTEC)

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

Osservatorio Astronomico di Padova

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 Research and Technology Centre (ESA ESTEC)

B.O. Demory

University of Bern

Anders Erikson

German Aerospace Center (DLR)

J. Farinato

Osservatorio Astronomico di Padova

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

Osservatorio Astronomico di Padova

L. Malvasio

University of Bern

L. Marafatto

Osservatorio Astronomico di Padova

H. Michaelis

German Aerospace Center (DLR)

M. Munari

Osservatorio Astrofisico di Catania

G. Olofsson

Stockholm University

H. Ottacher

Institut fur Weltraumforschung

R. Ottensamer

University of Vienna

I. Pagano

Osservatorio Astrofisico di Catania

E. Palle

Instituto Astrofisico de Canarias

G. Peter

German Aerospace Center (DLR)

D. Piazza

University of Bern

Giampaolo P. Piotto

Osservatorio Astronomico di Padova

Don L. Pollacco

The University of Warwick

Roberto Ragazzoni

Osservatorio Astronomico di Padova

N. Rando

European Space Research and Technology Centre (ESA ESTEC)

F. Ratti

European Space Research and Technology Centre (ESA ESTEC)

H. Rauer

German Aerospace Center (DLR)

I. Ribas

Institute of Space Sciences (ICE) - CSIC

M. Rieder

University of Bern

R. Rohlfs

University of Geneva

F. Safa

European Space Research and Technology Centre (ESA ESTEC)

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

Osservatorio Astronomico di Padova

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 A157

Subject Categories

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics

Control Engineering

DOI

10.1051/0004-6361/202039608

More information

Latest update

9/13/2021