The changing face of AU Mic b: Stellar spots, spin-orbit commensurability, and transit timing variations as seen by CHEOPS and TESS
Journal article, 2021

AU Mic is a young planetary system with a resolved debris disc showing signs of planet formation and two transiting warm Neptunes near mean-motion resonances. Here we analyse three transits of AU Mic b observed with the CHaracterising ExOPlanet Satellite (CHEOPS), supplemented with sector 1 and 27 Transiting Exoplanet Survey Satellite (TESS) photometry, and the All-Sky Automated Survey from the ground. The refined orbital period of AU Mic b is 8.462995 ± 0.000003 d, whereas the stellar rotational period is Prot = 4.8367 ± 0.0006 d. The two periods indicate a 7:4 spin-orbit commensurability at a precision of 0.1%. Therefore, all transits are observed in front of one of the four possible stellar central longitudes. This is strongly supported by the observation that the same complex star-spot pattern is seen in the second and third CHEOPS visits that were separated by four orbits (and seven stellar rotations). Using a bootstrap analysis we find that flares and star spots reduce the accuracy of transit parameters by up to 10% in the planet-to-star radius ratio and the accuracy on transit time by 3-4 min. Nevertheless, occulted stellar spot features independently confirm the presence of transit timing variations (TTVs) with an amplitude of at least 4 min. We find that the outer companion, AU Mic c, may cause the observed TTVs.

Planetary systems

Author

G.M. Szabó

Eötvös Loránd University (ELTE)

D. Gandolfi

Istituto nazionale di astrofisica (INAF)

A. Brandeker

Stockholm University

Szilard Csizmadia

German Aerospace Center (DLR)

Z. Garai

Eötvös Loránd University (ELTE)

Slovak Academy of Sciences

N. Billot

University of Geneva

C. Broeg

University of Bern

D. Ehrenreich

University of Geneva

A. Fortier

University of Bern

L. Fossati

Institut fur Weltraumforschung

S. Hoyer

Laboratoire d'Astrophysique de Marseille

L. Kiss

Eötvös Loránd University (ELTE)

Hungarian Academy of Sciences

The University of Sydney

A. L. des Etangs

Institut d 'Astrophysique de Paris

P. Maxted

Keele University

I. Ribas

Institute of Space Sciences (ICE) - CSIC

Institute of Space Studies of Catalonia (IEEC)

Y. Alibert

University of Bern

R. Alonso

Instituto de Astrofísica de Canarias

University of La Laguna

G. A. Escudé

Institute of Space Sciences (ICE) - CSIC

Institute of Space Studies of Catalonia (IEEC)

T. Bárczy

Admatis

S.C.C. Barros

University of Porto

D. Barrado

Centro de Astrobiologia (CAB)

W. Baumjohann

Institut fur Weltraumforschung

M. Beck

University of Geneva

T. Beck

University of Bern

A. Bekkelien

University of Geneva

X. Bonfils

Grenoble Alpes University

W. Benz

University of Bern

L. Borsato

Osservatorio Astronomico di Padova

M.-D. Busch

University of Bern

J. Cabrera

German Aerospace Center (DLR)

S. Charnoz

Institut de Physique du Globe de Paris

A. Collier Cameron

University of St Andrews

C. Corral Van Damme

European Space Research and Technology Centre (ESA ESTEC)

M. B. Davies

Lund University

L. Delrez

University of Liège

M. Deleuil

Laboratoire d'Astrophysique de Marseille

O. Demangeon

Laboratoire d'Astrophysique de Marseille

University of Porto

B.O. Demory

University of Bern

Anders Erikson

German Aerospace Center (DLR)

Malcolm Fridlund

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

Leiden University

D. Futyan

University of Geneva

A. Garciá Muñoz

Technische Universität Berlin

Michaël Gillon

University of Liège

M. Guedel

University of Vienna

P. Guterman

Institut National des Sciences de l'Univers

Laboratoire d'Astrophysique de Marseille

Kevin Heng

University of Bern

The University of Warwick

K. Isaak

European Space Research and Technology Centre (ESA ESTEC)

G. Lacedelli

Osservatorio Astronomico di Padova

University of Padua

J. Laskar

Paris Observatory

M. Lendl

University of Geneva

C. Lovis

University of Geneva

A. Luntzer

University of Vienna

D. Magrin

Osservatorio Astronomico di Padova

Valerio Nascimbeni

Osservatorio Astronomico di Padova

G. Olofsson

Stockholm University

H. P. Osborn

University of Bern

Massachusetts Institute of Technology (MIT)

R. Ottensamer

University of Vienna

I. Pagano

Osservatorio Astrofisico di Catania

Enric Palle

Instituto de Astrofísica de Canarias

University of La Laguna

G. Peter

German Aerospace Center (DLR)

D. Piazza

University of Bern

Giampaolo P. Piotto

Osservatorio Astronomico di Padova

University of Padua

Don L. Pollacco

The University of Warwick

D. Queloz

University of Cambridge

University of Geneva

Roberto Ragazzoni

Osservatorio Astronomico di Padova

University of Padua

N. Rando

European Space Research and Technology Centre (ESA ESTEC)

H. Rauer

German Aerospace Center (DLR)

Technische Universität Berlin

Freie Universität Berlin

N. C. Santos

University of Porto

Gaetano Scandariato

Osservatorio Astrofisico di Catania

D. Segransan

University of Geneva

L. M. Serrano

University of Turin

D. Sicilia

Osservatorio Astrofisico di Catania

A.E. Simon

University of Bern

Alexis M. S. Smith

German Aerospace Center (DLR)

S.G. Sousa

University of Porto

Manfred B. Steller

Institut fur Weltraumforschung

Nicolas Thomas

University of Bern

S. Udry

University of Geneva

V. Van Grootel

University of Liège

N. A. Walton

University of Cambridge

T.G. Wilson

University of St Andrews

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 654 A159

Subject Categories

Astronomy, Astrophysics and Cosmology

Other Physics Topics

Condensed Matter Physics

DOI

10.1051/0004-6361/202140345

More information

Latest update

11/12/2021