Pulsational amplitude growth of the star KIC 3429637 (HD 178875) in the context of Am and rho Puppis stars

TL;DR

This study investigates the intrinsic pulsational amplitude growth of the delta Sct star KIC 3429637, linking it to stellar evolution and comparing observations with time-dependent convection models.

Contribution

It provides the first detailed analysis of amplitude growth in KIC 3429637, confirming its classification as a marginal Am star and suggesting evolutionary changes as the cause.

Findings

Amplitude growth is intrinsic to the star, not instrumental.

Different growth rates observed for the three main pulsation peaks.

The star is confirmed as a marginal Am star.

Abstract

KIC 3429637 (HD 178875) is a delta Sct star whose light-curve shows continuous pulsational amplitude growth in Kepler Mission photometry. Analysis of the three largest amplitude peaks in the Fourier transform indicates different growth rates for all three. We have ruled out instrumental causes, and determine the amplitude growth to be intrinsic to the star. We calculate time-dependent convection models and compare them with the observations. We confirm earlier characterisations that KIC 3429637 is a marginal Am star through the analysis of new spectroscopic data. With the data presently available, a plausible cause of the amplitude growth is increasing pulsational driving as evolutionary changes shift the He II driving zone deeper in this rho Puppis star. If this model is correct, then we are watching real-time stellar evolutionary changes.