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Two Bright M Dwarfs Hosting Ultra-Short-Period Super-Earths with Earth-like Compositions

Hirano, Teruyuki and Livingston, John H. and Fukui, Akihiko and Narita, Norio and Harakawa, Hiroki and Ishikawa, Hiroyuki Tako and Miyakawa, Kohei and Kimura, Tadahiro and Nakayama, Akifumi and Fujita, Naho and Hori, Yasunori and Stassun, Keivan G. and Bieryla, Allyson and Cadieux, Charles and Ciardi, David R. and Collins, Karen A. and Ikoma, Masahiro and Vanderburg, Andrew and Barclay, Thomas and Brasseur, C. E. and de Leon, Jerome P. and Doty, John P. and Doyon, René and Esparza-Borges, Emma and Esquerdo, Gilbert A. and Furlan, Elise and Gaidos, Eric and Gonzales, Erica J. and Hodapp, Klaus and Howell, Steve B. and Isogai, Keisuke and Jacobson, Shane and Jenkins, Jon M. and Jensen, Eric L. N. and Kawauchi, Kiyoe and Kotani, Takayuki and Kudo, Tomoyuki and Kurita, Seiya and Kurokawa, Takashi and Kusakabe, Nobuhiko and Kuzuhara, Masayuki and Lafrenière, David and Latham, David W. and Massey, Bob and Mori, Mayuko and Murgas, Felipe and Nishikawa, Jun and Nishiumi, Taku and Omiya, Masashi and Paegert, Martin and Palle, Enric and Parviainen, Hannu and Quinn, Samuel N. and Ricker, George R. and Schwarz, Richard P. and Seager, Sara and Tamura, Motohide and Tenenbaum, Peter and Terada, Yuka and Vanderspek, Roland K. and Vievard, Sébastien and Watanabe, Noriharu and Winn, Joshua N. (2021) Two Bright M Dwarfs Hosting Ultra-Short-Period Super-Earths with Earth-like Compositions. Astronomical Journal, 162 (4). Art. No. 161. ISSN 0004-6256. doi:10.3847/1538-3881/ac0fdc.

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We present observations of two bright M dwarfs (TOI-1634 and TOI-1685: J = 9.5–9.6) hosting ultra-short-period (USP) planets identified by the TESS mission. The two stars are similar in temperature, mass, and radius (T_(eff) ≈ 3500 K, M⋆ ≈ 0.45–0.46 M_⊙, and R⋆ ≈ 0.45–0.46 R_⊙), and the planets are both super-Earth size (1.25 R_⊕ < R_p < 2.0 R_⊕). For both systems, light curves from ground-based photometry exhibit planetary transits, whose depths are consistent with those from the TESS photometry. We also refine the transit ephemerides based on the ground-based photometry, finding the orbital periods of P = 0.9893436 ± 0.0000020 days and P = 0.6691416 ± 0.0000019 days for TOI-1634b and TOI-1685b, respectively. Through intensive radial velocity (RV) observations using the InfraRed Doppler (IRD) instrument on the Subaru 8.2 m telescope, we confirm the planetary nature of the TOIs and measure their masses: 10.14 ± 0.95 M_⊕ and 3.43 ± 0.93 M_⊕ for TOI-1634b and TOI-1685b, respectively, when the observed RVs are fitted with a single-planet circular-orbit model. Combining those with the planet radii of R_p = 1.749 ± 0.079 R_⊕ (TOI-1634b) and 1.459 ± 0.065 R_⊕ (TOI-1685b), we find that both USP planets have mean densities consistent with an Earth-like internal composition, which is typical for small USP planets. TOI-1634b is currently the most massive USP planet in this category, and it resides near the radius valley, which makes it a benchmark planet in the context of discussing the size limit of rocky planet cores as well as testing the formation scenarios for USP planets. Excess scatter in the RV residuals for TOI-1685 suggests the presence of a possible secondary planet or unknown activity/instrumental noise in the RV data, but further observations are required to check those possibilities.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Hirano, Teruyuki0000-0003-3618-7535
Livingston, John H.0000-0002-4881-3620
Fukui, Akihiko0000-0002-4909-5763
Narita, Norio0000-0001-8511-2981
Harakawa, Hiroki0000-0002-6197-5544
Ishikawa, Hiroyuki Tako0000-0001-6309-4380
Miyakawa, Kohei0000-0002-5706-3497
Nakayama, Akifumi0000-0002-0998-0434
Fujita, Naho0000-0002-5791-970X
Hori, Yasunori0000-0003-4676-0251
Stassun, Keivan G.0000-0002-3481-9052
Bieryla, Allyson0000-0001-6637-5401
Cadieux, Charles0000-0001-9291-5555
Ciardi, David R.0000-0002-5741-3047
Collins, Karen A.0000-0001-6588-9574
Ikoma, Masahiro0000-0002-5658-5971
Vanderburg, Andrew0000-0001-7246-5438
Barclay, Thomas0000-0001-7139-2724
Brasseur, C. E.0000-0002-9314-960X
de Leon, Jerome P.0000-0002-6424-3410
Doty, John P.0000-0003-2996-8421
Doyon, René0000-0001-5485-4675
Esparza-Borges, Emma0000-0002-2341-3233
Esquerdo, Gilbert A.0000-0002-9789-5474
Furlan, Elise0000-0001-9800-6248
Gaidos, Eric0000-0002-5258-6846
Gonzales, Erica J.0000-0002-9329-2190
Hodapp, Klaus0000-0003-0786-2140
Howell, Steve B.0000-0002-2532-2853
Isogai, Keisuke0000-0002-6480-3799
Jenkins, Jon M.0000-0002-4715-9460
Jensen, Eric L. N.0000-0002-4625-7333
Kawauchi, Kiyoe0000-0003-1205-5108
Kotani, Takayuki0000-0001-6181-3142
Kudo, Tomoyuki0000-0002-9294-1793
Kusakabe, Nobuhiko0000-0001-9194-1268
Kuzuhara, Masayuki0000-0002-4677-9182
Lafrenière, David0000-0002-6780-4252
Latham, David W.0000-0001-9911-7388
Massey, Bob0000-0001-8879-7138
Mori, Mayuko0000-0003-1368-6593
Murgas, Felipe0000-0001-9087-1245
Nishikawa, Jun0000-0001-9326-8134
Nishiumi, Taku0000-0003-1510-8981
Omiya, Masashi0000-0002-5051-6027
Paegert, Martin0000-0001-8120-7457
Palle, Enric0000-0003-0987-1593
Parviainen, Hannu0000-0001-5519-1391
Quinn, Samuel N.0000-0002-8964-8377
Ricker, George R.0000-0003-2058-6662
Schwarz, Richard P.0000-0001-8227-1020
Seager, Sara0000-0002-6892-6948
Tamura, Motohide0000-0002-6510-0681
Tenenbaum, Peter0000-0002-1949-4720
Terada, Yuka0000-0003-2887-6381
Vanderspek, Roland K.0000-0001-6763-6562
Vievard, Sébastien0000-0003-4018-2569
Watanabe, Noriharu0000-0002-7522-8195
Winn, Joshua N.0000-0002-4265-047X
Additional Information:© 2021. The American Astronomical Society. Received 2021 March 23; revised 2021 June 5; accepted 2021 June 28; published 2021 September 23. Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. This work is partly supported by JSPS KAKENHI Grant Numbers JP20K14518, JP19K14783, JP18H01265, JP18H05439, JP17H04574, JP18H05442, JP15H02063, JP21H00035, and JP22000005; JST PRESTO grant No. JPMJPR1775; Grant-in-Aid for JSPS Fellows, grant No. JP20J21872; and a University Research Support Grant from the National Astronomical Observatory of Japan (NAOJ). J.N.W. thanks the Heising-Simons Foundation for support. The data analysis was carried out, in part, on the Multi-wavelength Data Analysis System operated by the Astronomy Data Center (ADC), National Astronomical Observatory of Japan. Based on observations obtained at the Observatoire du Mont-Mégantic, financed by Université de Montréal, Université Laval, the National Sciences and Engineering Council of Canada (NSERC), the Fonds québécois de la recherche sur la Nature et les technologies (FQRNT), and the Canada Economic Development program and the Quebec Ministère de l'Économie et de l'Innovation. This paper includes data collected by the TESS mission. Funding for the TESS mission is provided by the NASA Explorer Program. We acknowledge the use of TESS Alert data, which is currently in a beta test phase, from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. 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 research has made use of the Exoplanet Follow-up Observation Program 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 work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This work was enabled by observations made from the Subaru, Gemini North, and Keck telescopes, located within the Maunakea Science Reserve and adjacent to the summit of Maunakea. We are grateful for the privilege of observing the universe from a place that is unique in both its astronomical quality and its cultural significance. Some of the Observations in the paper made use of the High-Resolution Imaging instrument 'Alopeke. 'Alopeke was funded by the NASA Exoplanet Exploration Program and built at the NASA Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett Quigley. Data were reduced using a software pipeline originally written by Elliott Horch and Mark Everett. 'Alopeke was mounted on the Gemini North telescope of the international Gemini Observatory, a program of NSF's OIR Lab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). Data collected under program GN-2020B-LP-105. This paper is based on observations made with the MuSCAT2 instrument, developed by the Astrobiology Center, at Telescopio Carlos Sánchez operated on the island of Tenerife by the IAC in the Spanish Observatorio del Teide. This paper is based on observations made with the MuSCAT3 instrument, developed by the Astrobiology Center and under financial supports by JSPS KAKENHI (JP18H05439) and JST PRESTO (JPMJPR1775), at Faulkes Telescope North on Maui, HI, operated by the Las Cumbres Observatory. This work makes use of observations from the LCOGT network. Part of the LCOGT telescope time was granted by NOIRLab through the Mid-Scale Innovations Program (MSIP). MSIP is funded by NSF. We express special thanks to the anonymous referee for the helpful comments and suggestions on this manuscript. Facilities: Subaru (IRD) - , Gemini:Gillett ('Alopeke) - , Keck:II (NIRC2) - , LCOGT - , Okayama:1.88m(MuSCAT) - , Sanchez(MuSCAT2) - , FTN (MuSCAT3). - Software: AstroImageJ (Collins et al. 2017), IRAF (Tody 1993), SpecMatch-Emp (Yee et al. 2017), BANYAN Σ (Gagné et al. 2018), TAPIR (Jensen 2013).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Japan Society for the Promotion of Science (JSPS)JP20K14518
Japan Society for the Promotion of Science (JSPS)JP19K14783
Japan Society for the Promotion of Science (JSPS)JP18H01265
Japan Society for the Promotion of Science (JSPS)JP18H05439
Japan Society for the Promotion of Science (JSPS)JP17H04574
Japan Society for the Promotion of Science (JSPS)JP18H05442
Japan Society for the Promotion of Science (JSPS)JP15H02063
Japan Society for the Promotion of Science (JSPS)JP21H00035
Japan Society for the Promotion of Science (JSPS)JP22000005
Japan Science and Technology AgencyJPMJPR1775
Japan Society for the Promotion of Science (JSPS)JP20J21872
National Astronomical Observatory of JapanUNSPECIFIED
Heising-Simons FoundationUNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Japan Society for the Promotion of Science (JSPS)JP18H05439
Subject Keywords:High resolution spectroscopy; Radial velocity; Super Earths; Extrasolar rocky planets; Transit photometry
Issue or Number:4
Classification Code:Unified Astronomy Thesaurus concepts: High resolution spectroscopy (2096); Radial velocity (1332); Super Earths (1655); Extrasolar rocky planets (511); Transit photometry (1709)
Record Number:CaltechAUTHORS:20211014-212143005
Persistent URL:
Official Citation:Teruyuki Hirano et al 2021 AJ 162 161
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111447
Deposited By: George Porter
Deposited On:18 Oct 2021 22:42
Last Modified:18 Oct 2021 22:42

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