The discovery of differential radial rotation in the pulsating subdwarf B star KIC 3527751

TL;DR

This study analyzes three years of Kepler data on the pulsating subdwarf B star KIC 3527751, revealing differential radial rotation with a slower core and faster outer layers, marking the first such detection in this star type.

Contribution

The paper provides the first evidence of differential radial rotation in a subdwarf B star through detailed seismic analysis of pulsation modes.

Findings

Detection of 251 pulsation periods, confirming hybrid pulsator nature.

Identification of multiple mode multiplets, including ell=4 and possibly ell=9.

Evidence of differential rotation with the core rotating more slowly than the outer layers.

Abstract

We analyse three years of nearly-continuous Kepler spacecraft short cadence observations of the pulsating subdwarf B star KIC 3527751. We detect a total of 251 periodicities, most in the g-mode domain, but some where p-modes occur, confirming that KIC 3527751 is a hybrid pulsator. We apply seismic tools to the periodicities to characterize the properties of KIC 3527751. Techniques to identify modes include asymptotic period spacing relationships, frequency multiplets, and the separation of multiplet splittings. These techniques allow for 189 (75%) of the 251 periods to be associated with pulsation modes. Included in these are three sets of ell=4 multiplets and possibly an ell=9 multiplet. Period spacing sequences indicate ell=1 and 2 overtone spacings of 266.4 +/-0.2 and 153.2 +/-0.2 seconds, respectively. We also calculate reduced periods, from which we find evidence of trapped pulsations. Such mode trappings can be used to constrain the core/atmosphere transition layers. Interestingly, frequency multiplets in the g-mode region, which sample deep into the star, indicate a rotation period of 42.6 +/-3.4 days while p-mode multiplets, which sample the outer envelope, indicate a rotation period of 15.3 +/-0.7 days. We interpret this as differential rotation in the radial direction with the core rotating more slowly. This is the first example of differential rotation for a subdwarf B star.