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

December 2021 • 2021AJ....162..295C

Authors • 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

Abstract • 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.


IPAC Authors


Benjamin Fulton

Assistant Scientist