Breaking free seismic forward modelling from the surface effect

ABSTRACT Asteroseismology has revolutionized our understanding of stellar interiors, but systematic uncertainties in stellar models – particularly the near-surface effect – hinder precise comparisons between observations and theory. This study introduces BaseFM, a novel Bayesian framework for asteroseismic forward modelling that eliminates the need for ad hoc surface corrections. By marginalizing over frequency offsets and incorporating glitch signals from sharp structural variations, it delivers unbiased stellar parameters with improved accuracy. Validated against eclipsing binaries and interferometric measurements, the method achieves stellar parameters accurate to within about 1 per cent for stars across evolutionary stages, from Sun-like stars to red giants. Applying BaseFM to 70 stars in open clusters NGC 6791 and NGC 6819, consistent masses and ages are derived, confirming revised seismic scaling relations. The analysis reveals that classical surface corrections systematically overestimate stellar masses by about 5 per cent, and therefore underestimate the stellar age about 20 per cent. The true surface effect, on the other hand, exhibits a mass and/or metallicity-dependent trend incompatible with standard power-law assumptions. This work underscores the limitations of empirical surface corrections and provides a robust tool for stellar characterization. By bridging the gap between observations and models, BaseFM opens new avenues for probing physics in stars with outer convective layers that exhibit solar-type oscillations. The method’s success paves the way for future missions like PLATO, promising unprecedented precision in asteroseismic studies.