Asteroseismology of the ancient naked-eye exoplanet host star ν2 Lupi

ABSTRACT High-precision light curves from space-based telescopes and precise astrometry from the Gaia satellite have revolutionized our ability to characterize exoplanet host stars. Asteroseismology has allowed for stellar parameters to be determined to remarkable precision, achieving age uncertainties as low as 10−20 per cent for Sun-like stars. We present an asteroseismic analysis of the naked-eye ($V = 5.78$), G4V star $\nu ^2$ Lupi (HD 136352), which hosts three small transiting planets with orbital periods of 11, 27, and 107 d. We used the latest 20-s cadence photometry data from the Transiting Exoplanet Survey Satellite (TESS) to extract stellar oscillations. Comparing these to stellar models, we find that the star has a mass of $0.83^{+0.04}_{-0.03}$ (ran) $\pm 0.07$ (sys) $M_\odot$, a radius of $1.00^{+0.01}_{-0.02}$ (ran) $\pm 0.04$ (sys) $R_\odot$, and an age of $11.9^{+2.6}_{-1.6}$ (ran) $\pm 1.7$ (sys) Gyr. We also confirm that the star is likely a member of the Galactic thick disc based on its Galactic velocities, consistent with the asteroseismic age. Based on the newly determined stellar parameters, we recalculate the planet parameters. The inner planet has a mass of $4.55 \pm 0.40$ $M_{\oplus }$ and a radius of $1.57 \pm 0.04$ $R_{\oplus }$, suggesting the planet is rocky and consisting primarily of silicates without an iron-rich core, consistent with its old age and significant alpha-element enhancement. The two outer planets have masses and radii of $10.87 \pm 0.62$ $M_{\oplus }$ and $2.75 \pm 0.06$ $R_{\oplus }$, and $8.52 \pm 0.90$ $M_{\oplus }$ and $2.42 \pm 0.08$ $R_{\oplus }$, respectively, suggesting both are sub-Neptune planets with a significant H–He atmosphere.