@article{4fc087edb2004151890ef605ae600ef7,
title = "The TESS-Keck survey. II. An ultra-short-period rocky planet and its siblings transiting the galactic thick-disk star TOI-561",
abstract = "We report the discovery of TOI-561, a multiplanet system in the galactic thick disk that contains a rocky, ultrashort- period planet. This bright (V = 10.2) star hosts three small transiting planets identified in photometry from the NASA TESS mission: TOI-561 b (TOI-561.02, P = 0.44 days, Rp = 1.45 ± 0.11 R⊕), c (TOI-561.01, P = 10.8 days, Rp = 2.90 ± 0.13 R⊕), and d (TOI-561.03, P = 16.3 days, Rp = 2.32 ± 0.16 R⊕). The star is chemically ([Fe/ H] = -0.41 ± 0.05, [a/Fe]=+0.23 ± 0.05) and kinematically consistent with the galactic thick-disk population, making TOI-561 one of the oldest (10 ± 3 Gyr) and most metal-poor planetary systems discovered yet. We dynamically confirm planets b and c with radial velocities from the W. M. Keck Observatory High Resolution Echelle Spectrometer. Planet b has a mass and density of 3.2 ± 0.8M⊕ and 5.5+2.0-1.6g cm-3, consistent with a rocky composition. Its lower-than-average density is consistent with an iron-poor composition, although an Earth-like iron-to-silicates ratio is not ruled out. Planet c is 7.0 ± 2.3M⊕ and 1.6 ± 0.6 g cm-3, consistent with an interior rocky core overlaid with a low-mass volatile envelope. Several attributes of the photometry for planet d (which we did not detect dynamically) complicate the analysis, but we vet the planet with high-contrast imaging, groundbased photometric follow-up, and radial velocities. TOI-561 b is the first rocky world around a galactic thick-disk star confirmed with radial velocities and one of the best rocky planets for thermal emission studies.",
author = "Weiss, {Lauren M.} and Fei Dai and Daniel Huber and Brewer, {John M.} and Collins, {Karen A.} and Ciardi, {David R.} and Matthews, {Elisabeth C.} and Carl Ziegler and Howell, {Steve B.} and Batalha, {Natalie M.} and Crossfield, {Ian J.M.} and Courtney Dressing and Benjamin Fulton and Howard, {Andrew W.} and Howard Isaacson and Kane, {Stephen R.} and Petigura, {Erik A.} and Paul Robertson and Arpita Roy and Rubenzahl, {Ryan A.} and Twicken, {Joseph D.} and Claytor, {Zachary R.} and Stassun, {Keivan G.} and MacDougall, {Mason G.} and Ashley Chontos and Steven Giacalone and Dalba, {Paul A.} and Teov Mocnik and Hill, {Michelle L.} and Corey Beard and Murphy, {Joseph M.A.} and Rosenthal, {Lee J.} and Aida Behmard and {Van Zandt}, Judah and Jack Lubin and Kosiarek, {Molly R.} and Lund, {Michael B.} and Christiansen, {Jessie L.} and Matson, {Rachel A.} and Beichman, {Charles A.} and Schlieder, {Joshua E.} and Gonzales, {Erica J.} and C{\'e}sar Brice{\~n}o and Nicholas Law and Mann, {Andrew W.} and Collins, {Kevin I.} and Phil Evans and Akihiko Fukui and Jensen, {Eric L.N.} and Felipe Murgas and Norio Narita and Enric Palle and Hannu Parviainen and Schwarz, {Richard P.} and Tan, {Thiam Guan} and Acton, {Jack S.} and Bryant, {Edward M.} and Alexander Chaushev and Sam Gill and Philipp Eigm{\"u}ller and Jon Jenkins and George Ricker and Sara Seager and Winn, {Joshua N.}",
note = "Funding Information: This work makes use of observations from the LCOGT network. This article is based on observations made with the MuSCAT2 instrument, developed by ABC, at Telescopio Carlos S{\'a}nchez operated on the island of Tenerife by the IAC in the Spanish Observatorio del Teide. This work is partly supported by JSPS KAKENHI grant Nos. JP17H04574, JP18H01265, and JP18H05439, and JST PRESTO grant No. JPMJPR1775. This work makes use of data collected under the NGTS project at the ESO La Silla Paranal Observatory. The NGTS facility is operated by the consortium institutes with support from the UK Science and Technology Facilities Council (STFC) projects ST/M001962/1 and ST/S002642/1. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/ gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/ dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. J.S.J. acknowledges support by FONDECYT grant 1201371, and partial support from CONICYT project Basal AFB-170002. J.I.V. acknowledges support of CONICYT-PFCHA/Doctorado Nacional- 21191829. This research has made use of the Exoplanet Follow-up Observing Program (ExoFOP), which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration. 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. L.M.W. is supported by the Beatrice Watson Parrent Fellowship and NASA ADAP Grant 80NSSC19K0597. D.H. acknowledges support from the Alfred P. Sloan Foundation, the National Aeronautics and Space Administration (80NSSC18K1585, 80NSSC19K0379), and the National Science Foundation (AST- 1717000). E.A.P. acknowledges the support of the Alfred P. Sloan Foundation. C.D.D. acknowledges the support of the Hellman Family Faculty Fund, the Alfred P. Sloan Foundation, the David & Lucile Packard Foundation, and the National Aeronautics and Space Administration via the TESS Guest Investigator Program (80NSSC18K1583). I.J.M.C. acknowledges support from the NSF through grant AST-1824644. Z.R.C. acknowledges support from the TESS Guest Investigator Program (80NSSC18K18584). A.C. acknowledges support from the National Science Foundation through the Graduate Research Fellowship Program (DGE 1842402). P.D. acknowledges support from a National Science Foundation Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1903811. A.B. is supported by the NSF Graduate Research Fellowship, grant No. DGE 1745301. R.A.R. is supported by the NSF Graduate Research Fellowship, grant No. DGE 1745301. M.R.K. is supported by the NSF Graduate Research Fellowship, grant No. DGE 1339067. J.N.W. thanks the Heising Simons Foundation for support. Publisher Copyright: {\textcopyright} 2021. The American Astronomical Society. All rights reserved.",
year = "2021",
month = feb,
day = "1",
doi = "10.3847/1538-3881/abd409",
language = "English (US)",
volume = "161",
journal = "Astronomical Journal",
issn = "0004-6256",
publisher = "IOP Publishing Ltd.",
number = "2",
}