Diving Beneath the Sea of Stellar Activity: Chromatic Radial Velocities of the Young AU Mic Planetary System

Cale, Bryson L.; Reefe, Michael; Plavchan, Peter; Tanner, Angelle; Gaidos, Eric; Gagné, Jonathan; Gao, Peter; Kane, Stephen R.; Béjar, Víctor J. S.; Lodieu, Nicolas; Anglada-Escudé, Guillem; Ribas, Ignasi; Pallé, Enric; Quirrenbach, Andreas; Amado, Pedro J.; Reiners, Ansgar; Caballero, José A.; Rosa Zapatero Osorio, María; Dreizler, Stefan; Howard, Andrew W.; Fulton, Benjamin J.; Xuesong Wang, Sharon; Collins, Kevin I.; El Mufti, Mohammed; Wittrock, Justin; Gilbert, Emily A.; Barclay, Thomas; Klein, Baptiste; Martioli, Eder; Wittenmyer, Robert; Wright, Duncan; Addison, Brett; Hirano, Teruyuki; Tamura, Motohide; Kotani, Takayuki; Narita, Norio; Vermilion, David; Lee, Rena A.; Geneser, Claire; Teske, Johanna; Quinn, Samuel N.; Latham, David W.; Esquerdo, Gilbert A.; Calkins, Michael L.; Berlind, Perry; Zohrabi, Farzaneh; Stibbards, Caitlin; Kotnana, Srihan; Jenkins, Jon; Twicken, Joseph D.; Henze, Christopher; Kidwell, Richard; Burke, Christopher; Villaseñor, Joel; Boyd, Patricia
Bibliographical reference

The Astronomical Journal

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We present updated radial-velocity (RV) analyses of the AU Mic system. AU Mic is a young (22 Myr) early-M dwarf known to host two transiting planets-P b ~ 8.46 days, ${R}_{b}={4.38}_{-0.18}^{+0.18}\ {R}_{\oplus }$ , P c ~ 18.86 days, ${R}_{c}={3.51}_{-0.16}^{+0.16}\ {R}_{\oplus }$ . With visible RVs from Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical echelle Spectrographs (CARMENES)-VIS, CHIRON, HARPS, HIRES, MINERVA-Australis, and Tillinghast Reflector Echelle Spectrograph, as well as near-infrared (NIR) RVs from CARMENES-NIR, CSHELL, IRD, iSHELL, NIRSPEC, and SPIRou, we provide a 5σ upper limit to the mass of AU Mic c of M c ≤ 20.13 M ⊕ and present a refined mass of AU Mic b of ${M}_{b}={20.12}_{-1.57}^{+1.72}\ {M}_{\oplus }$ . Used in our analyses is a new RV modeling toolkit to exploit the wavelength dependence of stellar activity present in our RVs via wavelength-dependent Gaussian processes. By obtaining near-simultaneous visible and near-infrared RVs, we also compute the temporal evolution of RV "color" and introduce a regressional method to aid in isolating Keplerian from stellar activity signals when modeling RVs in future works. Using a multiwavelength Gaussian process model, we demonstrate the ability to recover injected planets at 5σ significance with semi-amplitudes down to ≍10 m s-1 with a known ephemeris, more than an order of magnitude below the stellar activity amplitude. However, we find that the accuracy of the recovered semi-amplitudes is ~50% for such signals with our model.
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