Discovery of 79 δ Scuti Stars in NGC 3532 Suggests a Decrease of Pulsator Occurrence with Age

Discovery of 79 δ Scuti Stars in NGC 3532 Suggests a Decrease of Pulsator Occurrence with Age

Many A–F type stars do not display δ Scuti pulsations, despite being located within the instability strip. Open clusters provide a unique opportunity to study δ Scuti pulsations among coeval populations with uniform chemical composition. Here we use data from the Transiting Exoplanet Survey Satellite Mission to discover 79 δ Scuti pulsators in the 300 Myr old open cluster NGC 3532, the largest number found within a single open cluster to date. We report a 50% ± 5% pulsator fraction in NGC 3532, considerably lower than in younger stellar populations, such the Pleiades (110 Myr), NGC 2516 (100 Myr), and the Cep-Her Complex (≤80 Myr), and similar to the pulsator fraction found among field star samples. We introduce the concept of pulsator occurrence, which corrects for incompleteness, and find it to be 63% ± 6%. For the stars that do pulsate, we find that the hotter stars occupy a distinct branch in the color–magnitude diagram due to faster rotation (>150 km s −1 ) than their nonpulsating counterparts. These results suggest that pulsator occurrence decreases with age and that rapid rotation is important in maintaining δ Scuti pulsations over time. We also investigate the period–luminosity (P–L) relation and the max–Teff relation of δ Scuti stars in NGC 3532. We find much scatter in the P–L relation of the dominant mode and two distinct branches in the max–Teff relation, similar to the Cep-Her Complex.