HD 20329b: An ultra-short-period planet around a solar-type star found by TESS^★

¹ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
e-mail: fmurgas@iac.es
² Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
³ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁴ NASA Exoplanet Science Institute-Caltech/IPAC, 1200 E. California Blvd. Pasadena, CA 91125, USA
⁵ Department of Physics, Engineering and Astronomy, Stephen F. Austin State University, 1936 North St, Nacogdoches, TX 75962, USA
⁶ Cerro Tololo Inter-American Observatory, Casilla 603, La Serena, Chile
⁷ Department of Physics and Astronomy, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255, USA
⁸ Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
⁹ Department of Multi-Disciplinary Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
¹⁰ Southwest Research Institute, 6220 Culebra Rd, San Antonio, TX 78238, USA
¹¹ Division of Geological and Planetary Sciences, 1200 E California Blvd, Pasadena, CA 91125, USA
¹² Department of Space, Earth and Environment, Astronomy and Plasma Physics, Chalmers University of Technology, 412 96 Gothenburg, Sweden
¹³ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
¹⁴ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹⁵ McDonald Observatory, The University of Texas at Austin, TX 78712, USA
¹⁶ Center for Planetary Systems Habitability, The University of Texas at Austin, Austin, TX 78712, USA
¹⁷ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
¹⁸ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
¹⁹ Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²⁰ Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²¹ NASA Ames Research Center, Moffett Field, CA 94035, USA
²² Center for Astrophysics ∣ Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
²³ Dipartimento di Fisica, Università di Torino, via P. Giuria 1, I-10125 Torino, Italy
²⁴ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
²⁵ Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²⁶ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²⁷ Department of Astronomy, The Graduate University for Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo, Japan
²⁸ Department of Astronomy & Astrophysics, University of Chicago, Chicago, IL 60637, USA
²⁹ Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
³⁰ Astronomical Institute of the Czech Academy of Sciences, Fričova 298, 25165, Ondřejov, Czech Republic
³¹ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy

Received: 8 July 2022
Accepted: 2 November 2022

Abstract

Context. Ultra-short-period (USP) planets are defined as planets with orbital periods shorter than one day. This type of planets is rare, highly irradiated, and interesting because their formation history is unknown.

Aims. We aim to obtain precise mass and radius measurements to confirm the planetary nature of a USP candidate found by the Transiting Exoplanet Survey Satellite (TESS). These parameters can provide insights into the bulk composition of the planet candidate and help to place constraints on its formation history.

Methods. We used TESS light curves and HARPS-N spectrograph radial velocity measurements to establish the physical properties of the transiting exoplanet candidate found around the star HD 20329 (TOI-4524). We performed a joint fit of the light curves and radial velocity time series to measure the mass, radius, and orbital parameters of the candidate.

Results. We confirm and characterize HD 20329b, a USP planet transiting a solar-type star. The host star (HD 20329, V = 8.74 mag, J = 7.5 mag) is characterized by its G5 spectral type with M_* = 0.90 ± 0.05 M_⊙, R_* = 1.13 ± 0.02 R_⊙, and T_eff = 5596 ± 50 K; it is located at a distance d = 63.68 ± 0.29 pc. By jointly fitting the available TESS transit light curves and follow-up radial velocity measurements, we find an orbital period of 0.9261 ± (0.5 × 10⁻⁴) days, a planetary radius of 1.72 ± 0.07 R_⊗, and a mass of 7.42 ± 1.09 M_⊗, implying a mean density of ρ_p = 8.06 ± 1.53 g cm⁻³. HD 20329b joins the ~30 currently known USP planets with radius and Doppler mass measurements.