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

Gy M Szabo; D Gandolfi; A Brandeker; S Csizmadia; Z Garai; N Billot; C Broeg; D Ehrenreich; A Fortier; L Fossati; S Hoyer; L Kiss; A Lecavelier des Etangs; PFL Maxted; I Ribas; Y Alibert; R Alonso; GA Escude; T Barczy; SCC Barros; D Barrado; W Baumjohann; M Beck; T Beck; A Bekkelien; X Bonfils; W Benz; L Borsato; MD Busch; J Cabrera; S Charnoz; AC Cameron; CC Van Damme; MB Davies; L Delrez; M Deleuil; ODS Demangeon; BO Demory; A Erikson; M Fridlund; D Futyan; A García Muñoz; M Gillon; M Guedel; P Guterman; K Heng; KG Isaak; G Lacedelli; J Laskar; M Lendl; C Lovis; A Luntzer; D Magrin; V Nascimbeni; G Olofsson; HP Osborn; R Ottensamer; I Pagano; E Palle; G Peter; D Piazza; G Piotto; D Pollacco; D Queloz; R Ragazzoni; N Rando; H Rauer; NC Santos; G Scandariato; D Segransan; LM Serrano; D Sicilia; AE Simon; AMS Smith; SG Sousa; M Steller; N Thomas; S Udry; V Van Grootel; NA Walton; TG Wilson

doi:10.1051/0004-6361/202140345

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

Gy M Szabo, D Gandolfi, A Brandeker, S Csizmadia, Z Garai, N Billot, C Broeg, D Ehrenreich, A Fortier, L Fossati, S Hoyer, L Kiss, A Lecavelier des Etangs, PFL Maxted, I Ribas, Y Alibert, R Alonso, GA Escude, T Barczy, SCC BarrosD Barrado, W Baumjohann, M Beck, T Beck, A Bekkelien, X Bonfils, W Benz, L Borsato, MD Busch, J Cabrera, S Charnoz, AC Cameron, CC Van Damme, MB Davies, L Delrez, M Deleuil, ODS Demangeon, BO Demory, A Erikson, M Fridlund, D Futyan, A García Muñoz, M Gillon, M Guedel, P Guterman, K Heng, KG Isaak, G Lacedelli, J Laskar, M Lendl, C Lovis, A Luntzer, D Magrin, V Nascimbeni, G Olofsson, HP Osborn, R Ottensamer, I Pagano, E Palle, G Peter, D Piazza, G Piotto, D Pollacco, D Queloz, R Ragazzoni, N Rando, H Rauer, NC Santos, G Scandariato, D Segransan, LM Serrano, D Sicilia, AE Simon, AMS Smith, SG Sousa, M Steller, N Thomas, S Udry, V Van Grootel, NA Walton, TG Wilson

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Abstract

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 P-rot = 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.

Original language	English
Article number	A159
Number of pages	15
Journal	Astronomy & Astrophysics
Volume	654
Early online date	26 Oct 2021
DOIs	https://doi.org/10.1051/0004-6361/202140345
Publication status	Published - Oct 2021

Keywords

Planetary systems

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Szabó_2021_AA_Changing-face-Au-Mic-b_VoR
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https://arxiv.org/abs/2108.02149

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Szabo, G. M., Gandolfi, D., Brandeker, A., Csizmadia, S., Garai, Z., Billot, N., Broeg, C., Ehrenreich, D., Fortier, A., Fossati, L., Hoyer, S., Kiss, L., Lecavelier des Etangs, A., Maxted, PFL., Ribas, I., Alibert, Y., Alonso, R., Escude, GA., Barczy, T., ... Wilson, TG. (2021). The changing face of AU Mic b: stellar spots, spin-orbit commensurability, and transit timing variations as seen by CHEOPS and TESS. Astronomy & Astrophysics, 654, Article A159. https://doi.org/10.1051/0004-6361/202140345

@article{7aa91fc08cc842cfaa68d4db19fd2077,

title = "The changing face of AU Mic b: stellar spots, spin-orbit commensurability, and transit timing variations as seen by CHEOPS and TESS",

abstract = "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 P-rot = 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.",

keywords = "Planetary systems",

author = "Szabo, \{Gy M\} and D Gandolfi and A Brandeker and S Csizmadia and Z Garai and N Billot and C Broeg and D Ehrenreich and A Fortier and L Fossati and S Hoyer and L Kiss and \{Lecavelier des Etangs\}, A and PFL Maxted and I Ribas and Y Alibert and R Alonso and GA Escude and T Barczy and SCC Barros and D Barrado and W Baumjohann and M Beck and T Beck and A Bekkelien and X Bonfils and W Benz and L Borsato and MD Busch and J Cabrera and S Charnoz and AC Cameron and \{Van Damme\}, CC and MB Davies and L Delrez and M Deleuil and ODS Demangeon and BO Demory and A Erikson and M Fridlund and D Futyan and Mu{\~n}oz, \{A Garc{\'i}a\} and M Gillon and M Guedel and P Guterman and K Heng and KG Isaak and G Lacedelli and J Laskar and M Lendl and C Lovis and A Luntzer and D Magrin and V Nascimbeni and G Olofsson and HP Osborn and R Ottensamer and I Pagano and E Palle and G Peter and D Piazza and G Piotto and D Pollacco and D Queloz and R Ragazzoni and N Rando and H Rauer and NC Santos and G Scandariato and D Segransan and LM Serrano and D Sicilia and AE Simon and AMS Smith and SG Sousa and M Steller and N Thomas and S Udry and \{Van Grootel\}, V and NA Walton and TG Wilson",

note = "A.C.C. and T.W. acknowledge support from STFC consolidated grant number ST/M001296/1.",

year = "2021",

month = oct,

doi = "10.1051/0004-6361/202140345",

language = "English",

volume = "654",

journal = "Astronomy \& Astrophysics",

issn = "0004-6361",

publisher = "EDP Sciences",

}

Szabo, GM, Gandolfi, D, Brandeker, A, Csizmadia, S, Garai, Z, Billot, N, Broeg, C, Ehrenreich, D, Fortier, A, Fossati, L, Hoyer, S, Kiss, L, Lecavelier des Etangs, A, Maxted, PFL, Ribas, I, Alibert, Y, Alonso, R, Escude, GA, Barczy, T, Barros, SCC, Barrado, D, Baumjohann, W, Beck, M, Beck, T, Bekkelien, A, Bonfils, X, Benz, W, Borsato, L, Busch, MD, Cabrera, J, Charnoz, S, Cameron, AC, Van Damme, CC, Davies, MB, Delrez, L, Deleuil, M, Demangeon, ODS, Demory, BO, Erikson, A, Fridlund, M, Futyan, D, Muñoz, AG, Gillon, M, Guedel, M, Guterman, P, Heng, K, Isaak, KG, Lacedelli, G, Laskar, J, Lendl, M, Lovis, C, Luntzer, A, Magrin, D, Nascimbeni, V, Olofsson, G, Osborn, HP, Ottensamer, R, Pagano, I, Palle, E, Peter, G, Piazza, D, Piotto, G, Pollacco, D, Queloz, D, Ragazzoni, R, Rando, N, Rauer, H, Santos, NC, Scandariato, G, Segransan, D, Serrano, LM, Sicilia, D, Simon, AE, Smith, AMS, Sousa, SG, Steller, M, Thomas, N, Udry, S, Van Grootel, V, Walton, NA & Wilson, TG 2021, 'The changing face of AU Mic b: stellar spots, spin-orbit commensurability, and transit timing variations as seen by CHEOPS and TESS', Astronomy & Astrophysics, vol. 654, A159. https://doi.org/10.1051/0004-6361/202140345

TY - JOUR

T1 - The changing face of AU Mic b

T2 - stellar spots, spin-orbit commensurability, and transit timing variations as seen by CHEOPS and TESS

AU - Szabo, Gy M

AU - Gandolfi, D

AU - Brandeker, A

AU - Csizmadia, S

AU - Garai, Z

AU - Billot, N

AU - Broeg, C

AU - Ehrenreich, D

AU - Fortier, A

AU - Fossati, L

AU - Hoyer, S

AU - Kiss, L

AU - Lecavelier des Etangs, A

AU - Maxted, PFL

AU - Ribas, I

AU - Alibert, Y

AU - Alonso, R

AU - Escude, GA

AU - Barczy, T

AU - Barros, SCC

AU - Barrado, D

AU - Baumjohann, W

AU - Beck, M

AU - Beck, T

AU - Bekkelien, A

AU - Bonfils, X

AU - Benz, W

AU - Borsato, L

AU - Busch, MD

AU - Cabrera, J

AU - Charnoz, S

AU - Cameron, AC

AU - Van Damme, CC

AU - Davies, MB

AU - Delrez, L

AU - Deleuil, M

AU - Demangeon, ODS

AU - Demory, BO

AU - Erikson, A

AU - Fridlund, M

AU - Futyan, D

AU - Muñoz, A García

AU - Gillon, M

AU - Guedel, M

AU - Guterman, P

AU - Heng, K

AU - Isaak, KG

AU - Lacedelli, G

AU - Laskar, J

AU - Lendl, M

AU - Lovis, C

AU - Luntzer, A

AU - Magrin, D

AU - Nascimbeni, V

AU - Olofsson, G

AU - Osborn, HP

AU - Ottensamer, R

AU - Pagano, I

AU - Palle, E

AU - Peter, G

AU - Piazza, D

AU - Piotto, G

AU - Pollacco, D

AU - Queloz, D

AU - Ragazzoni, R

AU - Rando, N

AU - Rauer, H

AU - Santos, NC

AU - Scandariato, G

AU - Segransan, D

AU - Serrano, LM

AU - Sicilia, D

AU - Simon, AE

AU - Smith, AMS

AU - Sousa, SG

AU - Steller, M

AU - Thomas, N

AU - Udry, S

AU - Van Grootel, V

AU - Walton, NA

AU - Wilson, TG

N1 - A.C.C. and T.W. acknowledge support from STFC consolidated grant number ST/M001296/1.

PY - 2021/10

Y1 - 2021/10

N2 - 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 P-rot = 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.

AB - 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 P-rot = 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.

KW - Planetary systems

UR - https://www.scopus.com/pages/publications/85118444840

U2 - 10.1051/0004-6361/202140345

DO - 10.1051/0004-6361/202140345

M3 - Article

SN - 0004-6361

VL - 654

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

M1 - A159

ER -

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

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Astronomy at St Andrews 2018-2021: Astronomy at St Andrews 2018-2021

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

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Astronomy at St Andrews 2018-2021: Astronomy at St Andrews 2018-2021

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