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

Creators: 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.; Zapatero Osorio, María Rosa; Dreizler, Stefan; Howard, Andrew W.; Fulton, Benjamin J.; Wang, Sharon Xuesong; 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 C., Jr.; Burke, Christopher; Villasenor, 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⊕, P_c ∼ 18.86 days, R_c = 3.51^(+0.16)_(−0.16) R⊕. 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^(+1.72)_(−1.57) M_⊕. 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.

Additional Information

© 2021. The American Astronomical Society. Received 2021 July 1; revised 2021 September 14; accepted 2021 October 1; published 2021 December 7. We thank all support astronomers, observers, and engineers from all facilities in helping enable the collection of the data presented in this paper. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community, where the iSHELL, HIRES, IRD, and SPIRou observations were recorded. We are most fortunate to have the opportunity to conduct observations from this mountain. This work is supported by grants to Peter Plavchan from NASA (awards 80NSSC20K0251 and 80NSSC21K0349), the National Science Foundation (Astronomy and Astrophysics grants 1716202 and 2006517), and the Mount Cuba Astronomical Foundation. Emily A. Gilbert also wishes to thank the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining Grant #1829740, the Brinson Foundation, and the Moore Foundation; her participation in the program has benefited this work. Emily is thankful for support from GSFC Sellers Exoplanet Environments Collaboration (SEEC), which is funded by the NASA Planetary Science Division's Internal Scientist Funding Model. The material is based upon work supported by NASA under award number 80GSFC21M0002. This work is partly supported by JSPS KAKENHI grant No. JP18H05439, JST PRESTO grant No. JPMJPR1775, the Astrobiology Center of National Institutes of Natural Sciences (NINS) (grant No. AB031010). M.T. is supported by JSPS KAKENHI grant Nos. 18H05442, 15H02063, and 22000005. The authors also with to acknowledge funding from the Agencia Estatal de Investigación del Ministerio de Ciencia e Innovación (AEI-MCINN) under grant PID2019-109522GB-C53. The authors also wish to thank the California Planet Search (CPS) collaboration for carrying out the HIRES observations recorded in 2020 presented in this work. Minerva-Australis is supported by Australian Research Council LIEF Grant LE160100001, Discovery Grant DP180100972, Mount Cuba Astronomical Foundation, and institutional partners University of Southern Queensland, UNSW Australia, MIT, Nanjing University, George Mason University, University of Louisville, University of California Riverside, University of Florida, and The University of Texas at Austin. CARMENES is an instrument at the Centro Astronómico Hispano-Alemán de Calar Alto (CAHA, Almería, Spain). CARMENES is funded by the German Max-Planck-Gesellschaft (MPG), the Spanish Consejo Superior de Investigaciones Científicas (CSIC), the European Union through FEDER/ERF FICTS-2011-02 funds, and the members of the CARMENES Consortium (Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Andalucía, Landessternwarte Köonigstuhl, Institut de Ciències de l'Espai, Institut für Astrophysik Göttingen, Universidad Complutense de Madrid, Thüringer Landessternwarte Tautenburg, Instituto de Astrofísica de Canarias, Hamburger Sternwarte, Centro de Astrobiología and Centro Astronómico Hispano-Alemán), with additional contributions by the Spanish Ministry of Economy, the German Science Foundation through the Major Research Instrumentation Programme and DFG Research Unit FOR2544 "Blue Planets around Red Stars," the Klaus Tschira Stiftung, the states of Baden-Württemberg and Niedersachsen, and by the Junta de Andalucía. We acknowledge financial support from the Agencia Estatal de Investigación of the Ministerio de Ciencia, Innovación y Universidades and the ERDF through projects PID2019-109522GB-C5[1:4]/AEI/10.13039/501100011033, PGC2018-098153-B-C33, and the Centre of Excellence "Severo Ochoa" and "María de Maeztu" awards to the Instituto de Astrofísica de Canarias (CEX2019-000920-S), Instituto de Astrofísica de Andalucía (SEV-2017-0709), and Centro de Astrobiología (MDM-2017-0737), and the Generalitat de Catalunya/CERCA program. This paper includes data collected by the NASA TESS mission that are publicly available from the Mikulski Archive for Space Telescopes (MAST). Funding for the TESS mission is provided by NASA's Science Mission Directorate. We acknowledge the use of public TESS data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center (Jenkins et al. 2016). Baptiste Klein acknowledges funding from the European Research Council under the European Union's Horizon 2020 research and innovation program (grant agreement No. 865624, GPRV). Eder Martioli acknowledges funding from the French National Research Agency (ANR) under contract number ANR-18-CE31-0019 (SPlaSH). Software: pychell (Cale et al. 2019), optimize, 55 Matplotlib (Hunter 2007), SciPy (Virtanen et al. 2020), NumPy (Harris et al. 2020), Numba (Lam et al. 2015), corner (Foreman-Mackey et al. 2020), plotly (Inc., 2015), Gadfly Matplotlib theme https://gist.github.com/JonnyCBB/c464d302fefce4722fe6cf5f461114ea, emcee, (Foreman-Mackey et al. 2013).

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