2026/07/24 by Simon J. Murphy, Anuj Gautam
#astro-ph.SR
Interpreting the observed properties of intermediate-mass stars requires accounting for rotation, binarity, intrinsic population diversity, and measurement uncertainty. We combine these effects in population-synthesis models of 1.4-2.5 M\odot stars that include pulsation properties of δ Sct variables. The synthetic populations successfully reproduce the distributions of stars observed in young associations, validating the mapping between intrinsic and observed stellar properties. Using these models, we infer a semi-empirical δ Sct instability strip by matching synthetic and observed populations. The resulting instability strip is systematically hotter than widely used theoretical prescriptions, implying that δ Sct stars are on average 0.1 M\odot more massive than previously assumed, with 95% of the population spanning approximately 1.50-2.30 M\odot. We then investigate the δ Sct period-luminosity relation and reproduce its recently identified second ridge with mixture models in which roughly one-third of stars have the fifth or sixth radial overtone as their dominant mode; the fraction increases in younger populations. In contrast, unresolved binarity does not account for the second ridge. Finally, we predict the population-wide distribution of asteroseismic large separations, Δν, finding a peak between 6 and 7 d-1, in agreement with recent observations. We also demonstrate that Δν is most reliably measured with the échelle technique, while autocorrelation methods can produce spurious detections when used in isolation. These results show that population synthesis provides a powerful framework for interpreting populations of δ Sct stars and for linking stellar evolution, pulsation, and observation.