Spots on Am stars

TL;DR

This study analyzes light variations in Am stars using Kepler data, revealing that many exhibit rotational modulation, flares, and pulsations, suggesting they may have significant magnetic fields and challenging existing diffusion-based theories.

Contribution

It provides the first extensive photometric analysis of Am stars, showing evidence of magnetic activity and pulsations that question current models of their metallicity enhancement.

Findings

Most Am stars show rotational modulation due to star spots.

A significant number of Am stars are δ Scuti variables.

Some Am stars exhibit flares, indicating magnetic activity.

Abstract

We investigate the light variations of 15 Am stars using four years of high-precision photometry from the Kepler spacecraft and an additional 14 Am stars from the K2 Campaign 0 field. We find that most of the Am stars in the Kepler field have light curves characteristic of rotational modulation due to star spots. Of the 29 Am stars observed, 12 are {\delta} Scuti variables and one is a {\gamma} Doradus star. One star is an eclipsing binary and another was found to be a binary from time-delay measurements. Two Am stars show evidence for flares which are unlikely to be due to a cool companion. The fact that 10 out of 29 Am stars are rotational variables and that some may even flare strongly suggests that Am stars possess significant magnetic fields. This is contrary to the current understanding that the enhanced metallicity in these stars is due to diffusion in the absence of a magnetic field. The fact that so many stars are {\delta} Scuti variables is also at odds with the prediction of diffusion theory. We suggest that a viable alternative is that the metal enhancement could arise from accretion.