TESS spots a mini-neptune interior to a hot saturn in the TOI-2000 system
Creators: name: Sha, Lizhou
name: Vanderburg, Andrew M.
name: Huang, Chelsea X.
name: Armstrong, David J.
name: Brahm, Rafael
name: Giacalone, Steven
name: Wood, Mackenna L.
name: Collins, Karen A.
name: Nielsen, Louise D.
name: Hobson, Melissa J.
name: Ziegler, Carl
name: Howell, Steve B.
name: Torres-Miranda, Pascal
name: Mann, Andrew W.
name: Zhou, George
name: Delgado-Mena, Elisa
name: Rojas, Felipe I.
name: Abe, Lyu
name: Trifonov, Trifon
name: Adibekyan, Vardan
name: Sousa, Sérgio G.
name: Fajardo-Acosta, Sergio B.
name: Guillot, Tristan
name: Howard, Saburo
name: Littlefield, Colin
name: Hawthorn, Faith
name: Schmider, François-Xavier
name: Eberhardt, Jan
name: Tan, Thiam-Guan
name: Osborn, Ares
name: Schwarz, Richard P.
name: Strøm, Paul
name: Jordán, Andrés
name: Wang, Gavin
name: Henning, Thomas
name: Massey, Bob
name: Law, Nicholas
name: Stockdale, Chris
name: Furlan, Elise
name: Srdoc, Gregor
name: Wheatley, Peter J.
name: Navascués, David Barrado
name: Lissauer, Jack J.
name: Stassun, Keivan G.
name: Ricker, George R.
name: Vanderspek, Roland K.
name: Latham, David W.
name: Winn, Joshua N.
name: Seager, Sara
name: Jenkins, Jon M.
name: Barclay, Thomas
name: Bouma, Luke G.
name: Christiansen, Jessie L.
name: Guerrero, Natalia
name: Rose, Mark E.
Publisher: name: arXiv
Year: 2022
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: Instrumentation and Methods for Astrophysics (astro-ph.IM)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Hot jupiters (P &lt; 10 d, M &gt; 60 $\mathrm{M}_\oplus$) are almost always found alone around their stars, but four out of hundreds known have inner companion planets. These rare companions allow us to constrain the hot jupiter's formation history by ruling out high-eccentricity tidal migration. Less is known about inner companions to hot Saturn-mass planets. We report here the discovery of the TOI-2000 system, which features a hot Saturn-mass planet with a smaller inner companion. The mini-neptune TOI-2000 b ($2.70 \pm 0.15 \,\mathrm{R}_\oplus$, $11.0 \pm 2.4 \,\mathrm{M}_\oplus$) is in a 3.10-day orbit, and the hot saturn TOI-2000 c ($8.14^{+0.31}_{-0.30} \,\mathrm{R}_\oplus$, $81.7^{+4.7}_{-4.6} \,\mathrm{M}_\oplus$) is in a 9.13-day orbit. Both planets transit their host star TOI-2000 (TIC 371188886, V = 10.98, TESS magnitude = 10.36), a metal-rich ([Fe/H] = $0.439^{+0.041}_{-0.043}$) G dwarf 174 pc away. TESS observed the two planets in sectors 9-11 and 36-38, and we followed up with ground-based photometry, spectroscopy, and speckle imaging. Radial velocities from CHIRON, FEROS, and HARPS allowed us to confirm both planets by direct mass measurement. In addition, we demonstrate constraining planetary and stellar parameters with MIST stellar evolutionary tracks through Hamiltonian Monte Carlo under the PyMC framework, achieving higher sampling efficiency and shorter run time compared to traditional Markov chain Monte Carlo. Having the brightest host star in the V band among similar systems, TOI-2000 b and c are superb candidates for atmospheric characterization by the JWST, which can potentially distinguish whether they formed together or TOI-2000 c swept along material during migration to form TOI-2000 b.
description: v3 adds RV frequency analysis; 25 pages, 11 figures, 14 tables; revision submitted to MNRAS; machine-readable tables available as ancillary files; posterior samples available from Zenodo at https://doi.org/10.5281/zenodo.7683293 and source code at https://doi.org/10.5281/zenodo.7988268