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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. 

Abstract The solar-type subgiantβHyi has long been studied as an old analog of the Sun. Although the rotation period has never been measured directly, it was estimated to be near 27 days. As a Southern Hemisphere target, it was not monitored by long-term stellar activity surveys, but archival International Ultraviolet Explorer data revealed a 12 yr activity cycle. Previous ground-based asteroseismology suggested that the star is slightly more massive and substantially larger and older than the Sun, so the similarity of both the rotation rate and the activity cycle period to solar values is perplexing. We use two months of precise time-series photometry from the Transiting Exoplanet Survey Satellite to detect solar-like oscillations inβHyi and determine the fundamental stellar properties from asteroseismic modeling. We also obtain a direct measurement of the rotation period, which was previously estimated from an ultraviolet activity–rotation relation. We then use rotational evolution modeling to predict the rotation period expected from either standard spin-down or weakened magnetic braking (WMB). We conclude that the rotation period ofβHyi is consistent with WMB and that changes in stellar structure on the subgiant branch can reinvigorate the large-scale dynamo and briefly sustain magnetic activity cycles. Our results support the existence of a “born-again” dynamo in evolved subgiants—previously suggested to explain the cycle in 94 Aqr Aa—which can best be understood within the WMB scenario. 

Abstract Hundreds of exoplanets between 1 and 1.8 times the size of Earth have been discovered on close-in orbits. However, these planets show such a diversity in densities that some appear to be made entirely of iron, while others appear to host gaseous envelopes. To test this diversity in composition, we update the masses of five rocky exoplanets (HD 93963 A b, Kepler-10 b, Kepler-100 b, Kepler-407 b, and TOI-1444 b) and present the confirmation of a new planet (TOI-1011) using 187 high-precision radial velocities from Gemini/MAROON-X and Keck/KPF. Our updated planet masses suggest compositions closer to that of Earth than previous literature values for all planets in our sample. In particular, we report that two previously identified “super-Mercuries” (Kepler-100 b and HD 93963 A b) have lower masses that suggest less iron-rich compositions. We then compare the ratio of iron to rock-building species with the abundance ratios of those elements in their host stars. These updated planet compositions do not suggest a steep relationship between planet and host star compositions, contradictory to previous results, and suggest that planets and host stars have similar abundance ratios.