Asteroseismology and Spectropolarimetry of the Exoplanet Host Star $\lambda$ Serpentis

TL;DR

This study combines asteroseismology, spectropolarimetry, and multi-wavelength observations to characterize the properties and evolutionary history of the exoplanet host star $\\lambda$ Serpentis, revealing insights into its magnetic activity, rotation, and age.

Contribution

The paper provides a comprehensive analysis of $\\lambda$ Ser using new asteroseismic, spectropolarimetric, and high-energy data, offering improved stellar characterization and evolutionary insights.

Findings

Detection of solar-like oscillations in TESS data.

Reconstruction of the star's magnetic field morphology.

Assessment of the star's rotational history and angular momentum loss.

Abstract

The bright star $\lambda$ Ser hosts a hot Neptune with a minimum mass of 13.6 $M_\oplus$ and a 15.5 day orbit. It also appears to be a solar analog, with a mean rotation period of 25.8 days and surface differential rotation very similar to the Sun. We aim to characterize the fundamental properties of this system, and to constrain the evolutionary pathway that led to its present configuration. We detect solar-like oscillations in time series photometry from the Transiting Exoplanet Survey Satellite (TESS), and we derive precise asteroseismic properties from detailed modeling. We obtain new spectropolarimetric data, and we use them to reconstruct the large-scale magnetic field morphology. We reanalyze the complete time series of chromospheric activity measurements from the Mount Wilson Observatory, and we present new X-ray and ultraviolet observations from the Chandra and Hubble space telescopes. Finally, we use the updated observational constraints to assess the rotational history of the star and to estimate the wind braking torque. We conclude that the remaining uncertainty on stellar age currently prevents an unambiguous interpretation of the properties of $\lambda$ Ser, and that the rate of angular momentum loss appears to be higher than for other stars with similar Rossby number. Future asteroseismic observations may help to improve the precision of the stellar age.