TESS Reveals HD 118203 b to be a Transiting Planet

TL;DR

TESS observations confirmed that HD 118203 b, previously known via radial velocity, transits its bright host star, enabling precise measurements of its size, mass, and orbital characteristics, and highlighting its potential for further atmospheric and stellar studies.

Contribution

First detection of transits for HD 118203 b, allowing detailed characterization of this bright host star's planet using TESS data.

Findings

Planet radius measured as 1.133 R_J.

Planet mass determined as 2.173 M_J.

Orbital period of 6.13498 days with eccentricity 0.316.

Abstract

The exoplanet HD 118203 b, orbiting a bright (V = 8.05) host star, was discovered using the radial velocity method by da Silva et al. (2006), but was not previously known to transit. TESS photometry has revealed that this planet transits its host star. Five planetary transits were observed by TESS, allowing us to measure the radius of the planet to be $1.133 \pm 0.031 R_J$, and to calculate the planet mass to be $2.173 \pm 0.078 M_J$. The host star is slightly evolved with an effective temperature of $T_{\rm eff} = 5692 \pm 83$ K and a surface gravity of ${\rm log}(g) = 3.891 \pm 0.019$. With an orbital period of $6.134980 \pm 0.000038$ days and an eccentricity of $0.316 \pm 0.021$, the planet occupies a transitional regime between circularized hot Jupiters and more dynamically active planets at longer orbital periods. The host star is among the ten brightest known to have transiting giant planets, providing opportunities for both planetary atmospheric and asteroseismic studies.