Transit Timing Variations for AU Microscopii b and c

Creators: Wittrock, Justin M.; Dreizler, Stefan; Reefe, Michael A.; Morris, Brett M.; Plavchan, Peter P.; Lowrance, Patrick J.; Demory, Brice-Olivier; Ingalls, James G.; Gilbert, Emily A.; Barclay, Thomas; Cale, Bryson L.; Collins, Karen A.; Collins, Kevin I.; Crossfield, Ian J. M.; Dragomir, Diana; Eastman, Jason D.; El Mufti, Mohammed; Feliz, Dax; Gagné, Jonathan; Gaidos, Eric; Gao, Peter; Geneser, Claire S.; Hebb, Leslie; Henze, Christopher E.; Horne, Keith D.; Jenkins, Jon M.; Jensen, Eric L. N.; Kane, Stephen R.; Kaye, Laurel; Martioli, Eder; Monsue, Teresa A.; Pallé, Enric; Quintana, Elisa V.; Radford, Don J.; Roccatagliata, Veronica; Schlieder, Joshua E.; Schwarz, Richard P.; Shporer, Avi; Stassun, Keivan G.; Stockdale, Christopher; Tan, Thiam-Guan; Tanner, Angelle M.; Vanderburg, Andrew; Vega, Laura D.; Wang, Songhu

Abstract

We explore the transit timing variations (TTVs) of the young (22 Myr) nearby AU Mic planetary system. For AU Mic b, we introduce three Spitzer (4.5 μm) transits, five TESS transits, 11 LCO transits, one PEST transit, one Brierfield transit, and two transit timing measurements from Rossiter–McLaughlin observations; for AU Mic c, we introduce three TESS transits. We present two independent TTV analyses. First, we use EXOFASTv2 to jointly model the Spitzer and ground-based transits and obtain the midpoint transit times. We then construct an O − C diagram and model the TTVs with Exo-Striker. Second, we reproduce our results with an independent photodynamical analysis. We recover a TTV mass for AU Mic c of 10.8_(-2.2)^(+2.3) M_⊕. We compare the TTV-derived constraints to a recent radial velocity (RV) mass determination. We also observe excess TTVs that do not appear to be consistent with the dynamical interactions of b and c alone or due to spots or flares. Thus, we present a hypothetical nontransiting "middle-d" candidate exoplanet that is consistent with the observed TTVs and candidate RV signal and would establish the AU Mic system as a compact resonant multiplanet chain in a 4:6:9 period commensurability. These results demonstrate that the AU Mic planetary system is dynamically interacting, producing detectable TTVs, and the implied orbital dynamics may inform the formation mechanisms for this young system. We recommend future RV and TTV observations of AU Mic b and c to further constrain the masses and confirm the existence of possible additional planet(s).

Additional Information

© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 November 10; revised 2022 March 28; accepted 2022 April 19; published 2022 June 30. P.P.P. acknowledges support from NASA (Exoplanet Research Program award No. 80NSSC20K0251, TESS Cycle 3 Guest Investigator Program award No. 80NSSC21K0349, JPL Research and Technology Development, and Keck Observatory Data Analysis), the NSF (Astronomy and Astrophysics grant Nos. 1716202 and 2006517), and the Mt. Cuba Astronomical Foundation. D.D. acknowledges support from the TESS Guest Investigator Program grant No. 80NSSC21K0108 and NASA Exoplanet Research Program grant No. 18-2XRP18_2-0136. E.G. acknowledges support from NASA Exoplanet Research Program award No. 80NSSC20K0251. The material is based upon work supported by NASA under award No. 80GSFC21M0002. L.D.V. acknowledges funding support from the Heising-Simons Astrophysics Postdoctoral Launch Program through a grant to Vanderbilt University. This paper includes data collected by the 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. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. This work is based in part on observations made with the Spitzer Space Telescope, which was operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. This research has made use of the NASA/IPAC Infrared Science Archive, which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology. This work makes use of observations from the Las Cumbres Observatory global telescope network. Part of the LCOGT telescope time was granted by NOIRLab through the Mid-Scale Innovations Program (MSIP). MSIP is funded by NSF. This research has made use of the PEST photometry pipeline 63 by Thiam-Guan Tan. This research has made use of the NASA Exoplanet Archive and the Exoplanet Follow-up Observation Program website, both of which are operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. This research has made use of NASA's Astrophysics Data System Bibliographic Services. This research has made use of an online calculator that converts a list of Barycentric Julian Dates in Barycentric Dynamical Time (BJD_TDB) to JD in UT (Eastman et al. 2010). We also give thanks to Trifon Trifonov for his assistance in the use of the Exo-Striker package and analysis of the AU Mic system. Facilities: Brierfield:0.36 m (Moravian G4-16000 KAF-16803), CFHT (SPIRou), ExoFOP, Exoplanet Archive, IRSA, LCOGT (SAAO:1 m and SSO:1 m; Sinistro), MAST, PEST:0.30 m (SBIG ST-8XME), Spitzer (IRAC), TESS, VLT:Antu (ESPRESSO). Software: AstroImageJ (Collins et al. 2017), astropy (Astropy Collaboration et al. 2013, 2018), batman (Kreidberg 2015), bayesflare (Pitkin et al. 2014), celerite (Foreman-Mackey et al. 2017), celerite2 (Foreman-Mackey et al. 2017; Foreman-Mackey 2018), emcee (Foreman-Mackey et al. 2013), EXOFASTv2 (Eastman et al. 2019), exoplanet (Foreman-Mackey et al. 2021), Exo-Striker (Trifonov 2019), fleck (Morris 2020), ipython (Pérez & Granger 2007), lightkurve (Lightkurve Collaboration et al. 2018), matplotlib (Hunter 2007), mercury6 (Chambers 1999), numpy (Harris et al. 2020), rebound (Rein & Liu 2012; Rein & Spiegel 2015), scipy (Virtanen et al. 2020), TAPIR (Jensen 2013), xoflares (Gilbert et al.2022).

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