One year of AU Mic with HARPS – I. Measuring the masses of the two transiting planets

Zicher, N.; Barragán, Oscar; Klein, Baptiste; Aigrain, S.; Owen, James E.; Gandolfi, D.; Lagrange, Anne-Marie; Serrano, L. M.; Kaye, Laurel; Nielsen, L. D.; Rajpaul, Vinesh; Grandjean, A.; Goffo, E.; Nicholson, Belinda

doi:10.1093/mnras/stac614

“…Only for ∼10% of these have the masses and radii been determined directly through observations, however. Only two systems, V 1298 Tau (Suárez Mascareño 2022) and AU Mic (Plavchan et al 2020 Zicher et al 2022), are younger than 50 Myr and have known planetary companions with such determinations. To constrain evolutionary models, we therefore need to know both quantities not only for a larger number of planets, but also for planets that are significantly younger (≪100 Myr) than those for which we currently have both parameters.…”

Section: Introductionmentioning

confidence: 99%

Radial velocity survey for planets around young stars (RVSPY)

Zakhozhay

¹

,

Launhardt

²

,

Trifonov

³

et al. 2022

A&A

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Aims. We aim to detect planetary companions to young stars with debris disks via the radial velocity method. Methods. We observed HD 114082 during April 2018 -august 2022 as one of the targets of our RV SPY program (Radial Velocity Survey for Planets around Young stars). We use the FEROS spectrograph, mounted to the MPG/ESO 2.2 m telescope in Chile, to obtain high signal-to-noise spectra and time series of precise radial velocities (RVs). Additionally, we analyze archival HARPS spectra and TESS photometric data. We use the CERES, CERES++ and SERVAL pipelines to derive RVs and activity indicators and ExoStriker for the independent and combined analysis of the RVs and TESS photometry. Results. We report the discovery of a warm super-Jovian companion around HD 114082 based on a 109.8±0.4 day signal in the combined RV data from FEROS and HARPS, and on one transit event in the TESS photometry. The best-fit model indicates a 8.0±1.0 M Jup companion with a radius of 1.00±0.03R Jup in an orbit with a semi-major axis of 0.51±0.01 au and an eccentricity of 0.4±0.04. The companions orbit is in agreement with the known near edge-on debris disk located at ∼28 au. HD 114082 b is possibly the youngest (15±6 Myr), and one of only three young (<100 Myr) giant planetary companions for which both their mass and radius have been determined observationally. It is probably the first properly model-constraining giant planet that allows distinguishing between hot and cold-start models. It is significantly more compatible with the cold-start model.

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“…However, their large sizes can be accommodated by invoking any of (i) larger core masses, (ii) more volatile-rich compositions, (iii) larger initial atmospheric mass fractions, or (iv) longer thermal cooling times. Secure mass measurements would help constrain this parameter space, but the ∼1 km s −1 spot-induced radial velocity semiamplitudes make measuring the Doppler orbits very difficult (Cale et al 2021;Klein et al 2022;Zicher et al 2022). Regardless, the new Kepler-1643, KOI-7368, and KOI-7913 systems do demonstrate that at least some planets at 40 Myr have sizes that are consistent with theoretical expectations for mini-Neptunes.…”

Section: Normal-sized Mini-neptunes Exist At 40 Myrmentioning

confidence: 73%

Kepler and the Behemoth: Three Mini-Neptunes in a 40 Million Year Old Association

Bouma

¹

,

Kerr

²

,

Curtis

³

et al. 2022

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Stellar positions and velocities from Gaia are yielding a new view of open cluster dispersal. Here we present an analysis of a group of stars spanning Cepheus (l = 100°) to Hercules (l = 40°), hereafter the Cep-Her complex. The group includes four Kepler objects of interest: Kepler-1643 b (R p = 2.32 ± 0.13 R ⊕, P = 5.3 days), KOI-7368 b (R p = 2.22 ± 0.12 R ⊕, P = 6.8 days), KOI-7913 Ab (R p = 2.34 ± 0.18 R ⊕, P = 24.2 days), and Kepler-1627 Ab (R p = 3.85 ± 0.11 R ⊕, P = 7.2 days). The latter Neptune-sized planet is in part of the Cep-Her complex called the δ Lyr cluster. Here we focus on the former three systems, which are in other regions of the association. Based on kinematic evidence from Gaia, stellar rotation periods from TESS, and spectroscopy, these three objects are also ≈40 million years (Myr) old. More specifically, we find that Kepler-1643 is 46 − 7 + 9 Myr old, based on its membership in a dense subcluster of the complex called RSG-5. KOI-7368 and KOI-7913 are 36 − 8 + 10 Myr old, and are in a diffuse region that we call CH-2. Based on the transit shapes and high-resolution imaging, all three objects are most likely planets, with false-positive probabilities of 6 × 10−9, 4 × 10−3, and 1 × 10−4 for Kepler-1643, KOI-7368, and KOI-7913, respectively. These planets demonstrate that mini-Neptunes with sizes of ≈2 Earth radii exist at ages of 40 Myr.

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“…where M p is the mass of the planet, m H is the mass of a hydrogen atom, k B is the Boltzmann constant, T exo is the temperature at the exobase, and R exo is the radius of the exobase. We calculate the Jeans parameter, λ J , for AU Mic b and c using the lower mass estimates from Zicher et al (2022). We calculate λ J,b = 1.8 and λ J,c = 12.8 using the following two scaled relationships:…”

Section: Flare-driven Thermal Mass Lossmentioning

confidence: 99%

AU Microscopii in the Far-UV: Observations in Quiescence, during Flares, and Implications for AU Mic b and c

Feinstein¹,

France²,

Youngblood³

et al. 2022

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High-energy X-ray and ultraviolet (UV) radiation from young stars impacts planetary atmospheric chemistry and mass loss. The active ∼22 Myr M dwarf AU Mic hosts two exoplanets orbiting interior to its debris disk. Therefore, this system provides a unique opportunity to quantify the effects of stellar X-ray and UV irradiation on planetary atmospheres as a function of both age and orbital separation. In this paper, we present over 5 hr of far-UV (FUV) observations of AU Mic taken with the Cosmic Origins Spectrograph (COS; 1070-1360 Å) on the Hubble Space Telescope (HST). We provide an itemization of 120 emission features in the HST/COS FUV spectrum and quantify the flux contributions from formation temperatures ranging from 104 to 107 K. We detect 13 flares in the FUV white-light curve with energies ranging from 1029 to 1031 erg s. The majority of the energy in each of these flares is released from the transition region between the chromosphere and the corona. There is a 100× increase in flux at continuum wavelengths λ < 1100 Å in each flare, which may be caused by thermal Bremsstrahlung emission. We calculate that the baseline atmospheric mass-loss rate for AU Mic b is ∼108 g s−1, although this rate can be as high as ∼1014 g s−1 during flares with L flare ≃ 10 33 erg s−1. Finally, we model the transmission spectra for AU Mic b and c with a new panchromatic spectrum of AU Mic and motivate future JWST observations of these planets.

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One year of AU Mic with HARPS – I. Measuring the masses of the two transiting planets

Cited by 45 publications

References 96 publications

Radial velocity survey for planets around young stars (RVSPY)

Radial velocity survey for planets around young stars (RVSPY)

Kepler and the Behemoth: Three Mini-Neptunes in a 40 Million Year Old Association

AU Microscopii in the Far-UV: Observations in Quiescence, during Flares, and Implications for AU Mic b and c

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