Transmission spectroscopy and Rossiter-McLaughlin measurements of the young Neptune orbiting AU Mic

Πάλλη, Ε.; Oshagh, M.; Casasayas-Barris, N.; Hirano, Teruyuki; Stangret, M.; Luque, R.; Strachan, J. B. P.; Gaidos, Eric; Anglada-Escudé, G.; Plavchan, Peter; Addison, Brett C.

doi:10.1051/0004-6361/202038583

Cited by 59 publications

(46 citation statements)

References 67 publications

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“…The AU Mic host is an M1 star with a spatially resolved edge-on debris disk (Kalas et al 2004) and at least one transiting planet, AU Mic b (Plavchan et al 2020). This Neptune-size planet is in a 8.5-d prograde orbit aligned with the stellar rotation axis (Martioli et al 2020;Hirano et al 2020;Palle et al 2020). While Plavchan et al (2020) only reported an upper limit on the mass of AU Mic b, Klein et al (2021) measured 17.1 +4.7 −4.5 M ⊕ thanks to infrared observations secured with the SPIRou spectropolarimeter (Donati et al 2020).…”

Section: Introductionmentioning

confidence: 98%

New constraints on the planetary system around the young active star AU Mic

Martioli

Hébrard

Correia

et al. 2021

A&A

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AU Microscopii (AU Mic) is a young, active star whose transiting planet was recently detected. Here, we report our analysis of its TESS light curve, where we modeled the BY Draconis type quasi-periodic rotational modulation by starspots simultaneously to the flaring activity and planetary transits. We measured a flare occurrence rate in AU Mic of 6.35 flares per day for flares with amplitudes in the range of 0.06% < fmax < 1.5% of the star flux. We employed a Bayesian Markov chain Monte Carlo analysis to model the five transits of AU Mic b observed by TESS, improving the constraints on the planetary parameters. The measured planet-to-star effective radius ratio of Rp∕R⋆ = 0.0496 ± 0.0007 implies a physical radius of 4.07 ± 0.17 R⊕ and a planet density of 1.4 ± 0.4 g cm−3, confirming that AU Mic b is a Neptune-size moderately inflated planet. While a single feature possibly due to a second planet was previously reported in the former TESS data, we report the detection of two additional transit-like events in the new TESS observations of July 2020. This represents substantial evidence for a second planet (AU Mic c) in the system. We analyzed its three available transits and obtained an orbital period of 18.859019 ± 0.000016 d and a planetary radius of 3.24 ± 0.16 R⊕, which defines AU Mic c as a warm Neptune-size planet with an expected mass in the range of 2.2 M⊕ < Mc < 25.0 M⊕, estimated from the population of exoplanets of similar sizes. The two planets in the AU Mic system are in near 9:4 mean-motion resonance. We show that this configuration is dynamically stable and should produce transit-timing variations (TTV). Our non-detection of significant TTV in AU Mic b suggests an upper limit for the mass of AU Mic c of <7 M⊕, indicating that this planet is also likely to be inflated. As a young multi-planet system with at least two transiting planets, AU Mic becomes a key system for the study of atmospheres of infant planets and of planet-planet and planet-disk dynamics at the early stages of planetary evolution.

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Section: Introductionmentioning

confidence: 98%

New constraints on the planetary system around the young active star AU Mic

Martioli

Hébrard

Correia

et al. 2021

A&A

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“…It is expected that closeorbiting giant planets around such stars are aligned (Gaudi & Winn 2007;Winn et al 2010;Muñoz & Perets 2018;Louden et al 2021) because of strong tidal interactions with the stellar convective envelope. To date, there are only six other planets around M dwarfs with measured obliquities, namely GJ 436 b (Bourrier et al 2018), TRAPPIST-1 b, e, f (Hirano et al 2020a), AU Mic b (Addison et al 2021;Hirano et al 2020b;Palle et al 2020), and K2-25 b (Stefansson et al 2020). Determining the spin-orbit angle of TOI-1201 b is especially interesting in the context of the companion (320 au away) because it could hint possible interaction.…”

Section: Discussion and Future Prospectsmentioning

confidence: 99%

TOI-1201 b: A mini-Neptune transiting a bright and moderately young M dwarf

Kossakowski

Kemmer

Bluhm

et al. 2021

A&A

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We present the discovery of a transiting mini-Neptune around TOI-1201, a relatively bright and moderately young early M dwarf (J ≈ 9.5 mag, ~600–800 Myr) in an equal-mass ~8 arcsecond-wide binary system, using data from the Transiting Exoplanet Survey Satellite, along with follow-up transit observations. With an orbital period of 2.49 d, TOI-1201 b is a warm mini-Neptune with a radius of Rb = 2.415 ± 0.090 R⊕. This signal is also present in the precise radial velocity measurements from CARMENES, confirming the existence of the planet and providing a planetary mass of Mb = 6.28 ± 0.88 M⊕ and, thus, an estimated bulk density of 2.45−0.42+0.48 g cm−3. The spectroscopic observations additionally show evidence of a signal with a period of 19 d and a long periodic variation of undetermined origin. In combination with ground-based photometric monitoring from WASP-South and ASAS-SN, we attribute the 19 d signal to the stellar rotation period (Prot = 19–23 d), although we cannot rule out that the variation seen in photometry belongs to the visually close binary companion. We calculate precise stellar parameters for both TOI-1201 and its companion. The transiting planet is anexcellent target for atmosphere characterization (the transmission spectroscopy metric is 97−16+21) with the upcoming James Webb Space Telescope. It is also feasible to measure its spin-orbit alignment via the Rossiter-McLaughlin effect using current state-of-the-art spectrographs with submeter per second radial velocity precision.

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“…The sky-projected spin-orbit angle of AU Mic b has been measured by several authors: λ = −2.96 +10.44 −10.30 (Palle et al 2020); λ = 0 +18 −15 (Martioli et al 2020); λ = −4.7 +6.8 −6.4 (Hirano et al 2020); Notes. Time notation follows the ISO-8601 convention.…”

Section: Introductionmentioning

confidence: 99%

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

Szabó

Gandolfi

Brandeker

et al. 2021

A&A

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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.

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Transmission spectroscopy and Rossiter-McLaughlin measurements of the young Neptune orbiting AU Mic

Cited by 59 publications

References 67 publications

New constraints on the planetary system around the young active star AU Mic

New constraints on the planetary system around the young active star AU Mic

TOI-1201 b: A mini-Neptune transiting a bright and moderately young M dwarf

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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