Validating AU Microscopii d with Transit Timing Variations

Justin M. Wittrock; Peter P. Plavchan; Bryson L. Cale; Thomas Barclay; Mathis R. Ludwig; Richard P. Schwarz; Djamel Mekarnia; Amaury H. M. J. Triaud; Lyu Abe; Olga Suarez; Tristan Guillot; Dennis M. Conti; Karen A. Collins; Ian A. Waite; John F. Kielkopf; Kevin I. Collins; Stefan Dreizler; Mohammed El Mufti; Dax L. Feliz; Eric Gaidos; Claire S. Geneser; Keith D. Horne; Stephen R. Kane; Patrick J. Lowrance; Eder Martioli; Don J. Radford; Michael A. Reefe; Veronica Roccatagliata; Avi Shporer; Keivan G. Stassun; Chris Stockdale; Thiam-Guan Tan; Angelle M. Tanner; Laura D. Vega

doi:10.3847/1538-3881/acfda8

Validating AU Microscopii d with Transit Timing Variations

Justin M. Wittrock^*, Peter P. Plavchan, Bryson L. Cale, Thomas Barclay, Mathis R. Ludwig, Richard P. Schwarz, Djamel Mekarnia, Amaury H. M. J. Triaud, Lyu Abe, Olga Suarez, Tristan Guillot, Dennis M. Conti, Karen A. Collins, Ian A. Waite, John F. Kielkopf, Kevin I. Collins, Stefan Dreizler, Mohammed El Mufti, Dax L. Feliz, Eric GaidosClaire S. Geneser, Keith D. Horne, Stephen R. Kane, Patrick J. Lowrance, Eder Martioli, Don J. Radford, Michael A. Reefe, Veronica Roccatagliata, Avi Shporer, Keivan G. Stassun, Chris Stockdale, Thiam-Guan Tan, Angelle M. Tanner, Laura D. Vega

^*Corresponding author for this work

Physics and Astronomy

Research output: Contribution to journal › Article › peer-review

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Abstract

AU Mic is a young (22 Myr), nearby exoplanetary system that exhibits excess transit timing variations (TTVs) that cannot be accounted for by the two known transiting planets nor stellar activity. We present the statistical “validation” of the tentative planet AU Mic d (even though there are examples of “confirmed” planets with ambiguous orbital periods). We add 18 new transits and nine midpoint times in an updated TTV analysis to prior work. We perform the joint modeling of transit light curves using EXOFASTv2 and extract the transit midpoint times. Next, we construct an O−C diagram and use Exo-Striker to model the TTVs. We generate TTV log-likelihood periodograms to explore possible solutions for d’s period, then follow those up with detailed TTV and radial velocity Markov Chain Monte Carlo modeling and stability tests. We find several candidate periods for AU Mic d, all of which are near resonances with AU Mic b and c of varying order. Based on our model comparisons, the most-favored orbital period of AU Mic d is 12.73596 ± 0.00793 days (T_C,d = 2458340.55781 ± 0.11641 BJD), which puts the three planets near 4:6:9 mean-motion resonance. The mass for d is 1.053 ± 0.511 M_⊕, making this planet Earth-like in mass. If confirmed, AU Mic d would be the first known Earth-mass planet orbiting a young star and would provide a valuable opportunity in probing a young terrestrial planet’s atmosphere. Additional TTV observations of the AU Mic system are needed to further constrain the planetary masses, search for possible transits of AU Mic d, and detect possible additional planets beyond AU Mic c.

Original language	English
Article number	232
Number of pages	59
Journal	The Astronomical Journal
Volume	166
Issue number	6
Early online date	8 Nov 2023
DOIs	https://doi.org/10.3847/1538-3881/acfda8
Publication status	Published - 1 Dec 2023

Bibliographical note

Acknowledgments:
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) and the NSF (Astronomy and Astrophysics grants Nos. 1716202 and 2006517), and the Mt Cuba Astronomical Foundation.

E.G. acknowledges support from the NASA Exoplanets 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.

V.R. acknowledges the support of the Italian National Institute of Astrophysics (INAF) through the INAF GTO Grant "ERIS and SHARK GTO data exploitation."

This paper includes data collected by the TESS mission, which 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 made use of the PEST photometry pipeline 39 by Thiam-Guan Tan.

This work makes use of observations from the ASTEP telescope. ASTEP benefited from the support of the French and Italian polar agencies IPEV and PNRA in the framework of the Concordia station program, from OCA, INSU, and Idex UCAJEDI (ANR- 15-IDEX-01).

This research received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 803193/BEBOP), and from the Science and Technology Facilities Council (STFC; grant No. ST/S00193X/1).

This research has made use of the NASA Exoplanet Archive, which is 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 Exoplanet Follow-up Observation Program (ExoFOP; DOI: 10.26134/ExoFOP5) website, which is 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) 40 .

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: ASTEP 400:0.4m (FLI Proline 16800E) - , Brierfield:0.36m (Moravian G4-16000 KAF-16803) - , CFHT (SPIRou) - Canada-France-Hawaii Telescope, CHEOPS - , ExoFOP - , Exoplanet Archive - , IRSA - , IRTF (iSHELL) - Infrared Telescope Facility, LCOGT (CTIO:1m - , SAAO:1m - , SSO:1m - Siding Springs Observatory's 1 meter Telescope, and TO:1 m; Sinistro) - , MAST - , MKO CDK700:0.7m (U16) - , PEST:0.30m (SBIG ST-8XME) - , Spitzer (IRAC) - Spitzer Space Telescope satellite, TESS - , VLT:Antu (ESPRESSO) - Very Large Telescope (Antu)

Software: AstroImageJ (Collins et al. 2017), astropy (Astropy Collaboration et al. 2013, 2018), batman (Kreidberg 2015), celerite (Foreman-Mackey et al. 2017), celerite2 (Foreman-Mackey et al. 2017; Foreman-Mackey 2018), emcee (Foreman-Mackey et al. 2013), EXOFAST (Eastman et al. 2013), EXOFASTv2 (Eastman et al. 2019), exoplanet (Foreman-Mackey et al. 2021), Exo-Striker (Trifonov 2019), ipython (Perez & Granger 2007), lightkurve (Lightkurve Collaboration et al.), matplotlib (Hunter 2007), MEGNO (Cincotta & Simó 2000; Cincotta et al. 2003), numpy (Harris et al. 2020), rebound (Rein & Liu 2012; Rein & Spiegel 2015), scipy (Virtanen et al. 2020), SPOCK (Tamayo et al. 2020), TAPIR (Jensen 2013)

Keywords

Exoplanets
Exoplanet dynamics
Exoplanet astronomy
Exoplanet systems

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Wittrock, J. M., Plavchan, P. P., Cale, B. L., Barclay, T., Ludwig, M. R., Schwarz, R. P., Mekarnia, D., J. Triaud, A. H. M., Abe, L., Suarez, O., Guillot, T., Conti, D. M., Collins, K. A., Waite, I. A., Kielkopf, J. F., Collins, K. I., Dreizler, S., El Mufti, M., Feliz, D. L., ... Vega, L. D. (2023). Validating AU Microscopii d with Transit Timing Variations. The Astronomical Journal, 166(6), Article 232. https://doi.org/10.3847/1538-3881/acfda8

@article{6862a6aa07594730a7b3ae0e063cb203,

title = "Validating AU Microscopii d with Transit Timing Variations",

abstract = "AU Mic is a young (22 Myr), nearby exoplanetary system that exhibits excess transit timing variations (TTVs) that cannot be accounted for by the two known transiting planets nor stellar activity. We present the statistical “validation” of the tentative planet AU Mic d (even though there are examples of “confirmed” planets with ambiguous orbital periods). We add 18 new transits and nine midpoint times in an updated TTV analysis to prior work. We perform the joint modeling of transit light curves using EXOFASTv2 and extract the transit midpoint times. Next, we construct an O−C diagram and use Exo-Striker to model the TTVs. We generate TTV log-likelihood periodograms to explore possible solutions for d{\textquoteright}s period, then follow those up with detailed TTV and radial velocity Markov Chain Monte Carlo modeling and stability tests. We find several candidate periods for AU Mic d, all of which are near resonances with AU Mic b and c of varying order. Based on our model comparisons, the most-favored orbital period of AU Mic d is 12.73596 ± 0.00793 days (TC,d = 2458340.55781 ± 0.11641 BJD), which puts the three planets near 4:6:9 mean-motion resonance. The mass for d is 1.053 ± 0.511 M⊕, making this planet Earth-like in mass. If confirmed, AU Mic d would be the first known Earth-mass planet orbiting a young star and would provide a valuable opportunity in probing a young terrestrial planet{\textquoteright}s atmosphere. Additional TTV observations of the AU Mic system are needed to further constrain the planetary masses, search for possible transits of AU Mic d, and detect possible additional planets beyond AU Mic c.",

keywords = "Exoplanets, Exoplanet dynamics, Exoplanet astronomy, Exoplanet systems",

author = "Wittrock, {Justin M.} and Plavchan, {Peter P.} and Cale, {Bryson L.} and Thomas Barclay and Ludwig, {Mathis R.} and Schwarz, {Richard P.} and Djamel Mekarnia and {J. Triaud}, {Amaury H. M.} and Lyu Abe and Olga Suarez and Tristan Guillot and Conti, {Dennis M.} and Collins, {Karen A.} and Waite, {Ian A.} and Kielkopf, {John F.} and Collins, {Kevin I.} and Stefan Dreizler and {El Mufti}, Mohammed and Feliz, {Dax L.} and Eric Gaidos and Geneser, {Claire S.} and Horne, {Keith D.} and Kane, {Stephen R.} and Lowrance, {Patrick J.} and Eder Martioli and Radford, {Don J.} and Reefe, {Michael A.} and Veronica Roccatagliata and Avi Shporer and Stassun, {Keivan G.} and Chris Stockdale and Thiam-Guan Tan and Tanner, {Angelle M.} and Vega, {Laura D.}",

note = "Acknowledgments: 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) and the NSF (Astronomy and Astrophysics grants Nos. 1716202 and 2006517), and the Mt Cuba Astronomical Foundation. E.G. acknowledges support from the NASA Exoplanets 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. V.R. acknowledges the support of the Italian National Institute of Astrophysics (INAF) through the INAF GTO Grant {"}ERIS and SHARK GTO data exploitation.{"} This paper includes data collected by the TESS mission, which 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 made use of the PEST photometry pipeline 39 by Thiam-Guan Tan. This work makes use of observations from the ASTEP telescope. ASTEP benefited from the support of the French and Italian polar agencies IPEV and PNRA in the framework of the Concordia station program, from OCA, INSU, and Idex UCAJEDI (ANR- 15-IDEX-01). This research received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 803193/BEBOP), and from the Science and Technology Facilities Council (STFC; grant No. ST/S00193X/1). This research has made use of the NASA Exoplanet Archive, which is 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 Exoplanet Follow-up Observation Program (ExoFOP; DOI: 10.26134/ExoFOP5) website, which is 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) 40 . 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: ASTEP 400:0.4m (FLI Proline 16800E) - , Brierfield:0.36m (Moravian G4-16000 KAF-16803) - , CFHT (SPIRou) - Canada-France-Hawaii Telescope, CHEOPS - , ExoFOP - , Exoplanet Archive - , IRSA - , IRTF (iSHELL) - Infrared Telescope Facility, LCOGT (CTIO:1m - , SAAO:1m - , SSO:1m - Siding Springs Observatory's 1 meter Telescope, and TO:1 m; Sinistro) - , MAST - , MKO CDK700:0.7m (U16) - , PEST:0.30m (SBIG ST-8XME) - , Spitzer (IRAC) - Spitzer Space Telescope satellite, TESS - , VLT:Antu (ESPRESSO) - Very Large Telescope (Antu) Software: AstroImageJ (Collins et al. 2017), astropy (Astropy Collaboration et al. 2013, 2018), batman (Kreidberg 2015), celerite (Foreman-Mackey et al. 2017), celerite2 (Foreman-Mackey et al. 2017; Foreman-Mackey 2018), emcee (Foreman-Mackey et al. 2013), EXOFAST (Eastman et al. 2013), EXOFASTv2 (Eastman et al. 2019), exoplanet (Foreman-Mackey et al. 2021), Exo-Striker (Trifonov 2019), ipython (Perez & Granger 2007), lightkurve (Lightkurve Collaboration et al.), matplotlib (Hunter 2007), MEGNO (Cincotta & Sim{\'o} 2000; Cincotta et al. 2003), numpy (Harris et al. 2020), rebound (Rein & Liu 2012; Rein & Spiegel 2015), scipy (Virtanen et al. 2020), SPOCK (Tamayo et al. 2020), TAPIR (Jensen 2013)",

year = "2023",

month = dec,

day = "1",

doi = "10.3847/1538-3881/acfda8",

language = "English",

volume = "166",

journal = "The Astronomical Journal",

issn = "0004-6256",

publisher = "American Astronomical Society",

number = "6",

}

Wittrock, JM, Plavchan, PP, Cale, BL, Barclay, T, Ludwig, MR, Schwarz, RP, Mekarnia, D, J. Triaud, AHM, Abe, L, Suarez, O, Guillot, T, Conti, DM, Collins, KA, Waite, IA, Kielkopf, JF, Collins, KI, Dreizler, S, El Mufti, M, Feliz, DL, Gaidos, E, Geneser, CS, Horne, KD, Kane, SR, Lowrance, PJ, Martioli, E, Radford, DJ, Reefe, MA, Roccatagliata, V, Shporer, A, Stassun, KG, Stockdale, C, Tan, T-G, Tanner, AM & Vega, LD 2023, 'Validating AU Microscopii d with Transit Timing Variations', The Astronomical Journal, vol. 166, no. 6, 232. https://doi.org/10.3847/1538-3881/acfda8

TY - JOUR

T1 - Validating AU Microscopii d with Transit Timing Variations

AU - Wittrock, Justin M.

AU - Plavchan, Peter P.

AU - Cale, Bryson L.

AU - Barclay, Thomas

AU - Ludwig, Mathis R.

AU - Schwarz, Richard P.

AU - Mekarnia, Djamel

AU - J. Triaud, Amaury H. M.

AU - Abe, Lyu

AU - Suarez, Olga

AU - Guillot, Tristan

AU - Conti, Dennis M.

AU - Collins, Karen A.

AU - Waite, Ian A.

AU - Kielkopf, John F.

AU - Collins, Kevin I.

AU - Dreizler, Stefan

AU - El Mufti, Mohammed

AU - Feliz, Dax L.

AU - Gaidos, Eric

AU - Geneser, Claire S.

AU - Horne, Keith D.

AU - Kane, Stephen R.

AU - Lowrance, Patrick J.

AU - Martioli, Eder

AU - Radford, Don J.

AU - Reefe, Michael A.

AU - Roccatagliata, Veronica

AU - Shporer, Avi

AU - Stassun, Keivan G.

AU - Stockdale, Chris

AU - Tan, Thiam-Guan

AU - Tanner, Angelle M.

AU - Vega, Laura D.

N1 - Acknowledgments: 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) and the NSF (Astronomy and Astrophysics grants Nos. 1716202 and 2006517), and the Mt Cuba Astronomical Foundation. E.G. acknowledges support from the NASA Exoplanets 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. V.R. acknowledges the support of the Italian National Institute of Astrophysics (INAF) through the INAF GTO Grant "ERIS and SHARK GTO data exploitation." This paper includes data collected by the TESS mission, which 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 made use of the PEST photometry pipeline 39 by Thiam-Guan Tan. This work makes use of observations from the ASTEP telescope. ASTEP benefited from the support of the French and Italian polar agencies IPEV and PNRA in the framework of the Concordia station program, from OCA, INSU, and Idex UCAJEDI (ANR- 15-IDEX-01). This research received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 803193/BEBOP), and from the Science and Technology Facilities Council (STFC; grant No. ST/S00193X/1). This research has made use of the NASA Exoplanet Archive, which is 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 Exoplanet Follow-up Observation Program (ExoFOP; DOI: 10.26134/ExoFOP5) website, which is 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) 40 . 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: ASTEP 400:0.4m (FLI Proline 16800E) - , Brierfield:0.36m (Moravian G4-16000 KAF-16803) - , CFHT (SPIRou) - Canada-France-Hawaii Telescope, CHEOPS - , ExoFOP - , Exoplanet Archive - , IRSA - , IRTF (iSHELL) - Infrared Telescope Facility, LCOGT (CTIO:1m - , SAAO:1m - , SSO:1m - Siding Springs Observatory's 1 meter Telescope, and TO:1 m; Sinistro) - , MAST - , MKO CDK700:0.7m (U16) - , PEST:0.30m (SBIG ST-8XME) - , Spitzer (IRAC) - Spitzer Space Telescope satellite, TESS - , VLT:Antu (ESPRESSO) - Very Large Telescope (Antu) Software: AstroImageJ (Collins et al. 2017), astropy (Astropy Collaboration et al. 2013, 2018), batman (Kreidberg 2015), celerite (Foreman-Mackey et al. 2017), celerite2 (Foreman-Mackey et al. 2017; Foreman-Mackey 2018), emcee (Foreman-Mackey et al. 2013), EXOFAST (Eastman et al. 2013), EXOFASTv2 (Eastman et al. 2019), exoplanet (Foreman-Mackey et al. 2021), Exo-Striker (Trifonov 2019), ipython (Perez & Granger 2007), lightkurve (Lightkurve Collaboration et al.), matplotlib (Hunter 2007), MEGNO (Cincotta & Simó 2000; Cincotta et al. 2003), numpy (Harris et al. 2020), rebound (Rein & Liu 2012; Rein & Spiegel 2015), scipy (Virtanen et al. 2020), SPOCK (Tamayo et al. 2020), TAPIR (Jensen 2013)

PY - 2023/12/1

Y1 - 2023/12/1

N2 - AU Mic is a young (22 Myr), nearby exoplanetary system that exhibits excess transit timing variations (TTVs) that cannot be accounted for by the two known transiting planets nor stellar activity. We present the statistical “validation” of the tentative planet AU Mic d (even though there are examples of “confirmed” planets with ambiguous orbital periods). We add 18 new transits and nine midpoint times in an updated TTV analysis to prior work. We perform the joint modeling of transit light curves using EXOFASTv2 and extract the transit midpoint times. Next, we construct an O−C diagram and use Exo-Striker to model the TTVs. We generate TTV log-likelihood periodograms to explore possible solutions for d’s period, then follow those up with detailed TTV and radial velocity Markov Chain Monte Carlo modeling and stability tests. We find several candidate periods for AU Mic d, all of which are near resonances with AU Mic b and c of varying order. Based on our model comparisons, the most-favored orbital period of AU Mic d is 12.73596 ± 0.00793 days (TC,d = 2458340.55781 ± 0.11641 BJD), which puts the three planets near 4:6:9 mean-motion resonance. The mass for d is 1.053 ± 0.511 M⊕, making this planet Earth-like in mass. If confirmed, AU Mic d would be the first known Earth-mass planet orbiting a young star and would provide a valuable opportunity in probing a young terrestrial planet’s atmosphere. Additional TTV observations of the AU Mic system are needed to further constrain the planetary masses, search for possible transits of AU Mic d, and detect possible additional planets beyond AU Mic c.

AB - AU Mic is a young (22 Myr), nearby exoplanetary system that exhibits excess transit timing variations (TTVs) that cannot be accounted for by the two known transiting planets nor stellar activity. We present the statistical “validation” of the tentative planet AU Mic d (even though there are examples of “confirmed” planets with ambiguous orbital periods). We add 18 new transits and nine midpoint times in an updated TTV analysis to prior work. We perform the joint modeling of transit light curves using EXOFASTv2 and extract the transit midpoint times. Next, we construct an O−C diagram and use Exo-Striker to model the TTVs. We generate TTV log-likelihood periodograms to explore possible solutions for d’s period, then follow those up with detailed TTV and radial velocity Markov Chain Monte Carlo modeling and stability tests. We find several candidate periods for AU Mic d, all of which are near resonances with AU Mic b and c of varying order. Based on our model comparisons, the most-favored orbital period of AU Mic d is 12.73596 ± 0.00793 days (TC,d = 2458340.55781 ± 0.11641 BJD), which puts the three planets near 4:6:9 mean-motion resonance. The mass for d is 1.053 ± 0.511 M⊕, making this planet Earth-like in mass. If confirmed, AU Mic d would be the first known Earth-mass planet orbiting a young star and would provide a valuable opportunity in probing a young terrestrial planet’s atmosphere. Additional TTV observations of the AU Mic system are needed to further constrain the planetary masses, search for possible transits of AU Mic d, and detect possible additional planets beyond AU Mic c.

KW - Exoplanets

KW - Exoplanet dynamics

KW - Exoplanet astronomy

KW - Exoplanet systems

U2 - 10.3847/1538-3881/acfda8

DO - 10.3847/1538-3881/acfda8

M3 - Article

SN - 0004-6256

VL - 166

JO - The Astronomical Journal

JF - The Astronomical Journal

IS - 6

M1 - 232

ER -

Validating AU Microscopii d with Transit Timing Variations

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