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

Abstract

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. We confirm and characterize HD 20329b, an ultra-short-period (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 ${\mathrm{M}}_{\star }=0.90\pm 0.05$ M${}_{\odot }$, ${\mathrm{R}}_{\star }=1.13\pm 0.02$ R${}_{\odot }$, and ${\mathrm{T}}_{\mathrm{eff}}=5596\pm 50$ K; it is located at a distance $d=63.68\pm 0.29$ pc. By jointly fitting the available TESS transit light curves and follow-up radial velocity measurements, we find an orbital period of $0.9261\pm (0.5\times 10^{-4})$ days, a planetary radius of $1.72\pm 0.07$ ${\mathrm{R}}_{\oplus }$, and a mass of $7.42\pm 1.09$ ${\mathrm{M}}_{\oplus }$, implying a mean density of $\ddot{I}{}_{\mathrm{p}}=8.06\pm 1.53$ g cm${}^{-3}$. HD 20329b joins the $\sim$30 currently known USP planets with radius and Doppler mass measurements.

Accepted for publication in A&A, 26 pages