Spots on Am stars

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 δ Scuti variables and one is a γ 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 δ 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.

12 pages, 13 figures

References in corpus (2)

• Finding binaries among Kepler pulsating stars from phase modulation of their pulsations
• Fundamental parameters of 8 Am stars: comparing observations with theory

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• Metallic-Line Stars Identified from Low Resolution Spectra of LAMOST DR5
• Metal-Rich SX Phe stars in the Kepler Field
• Rotation and spots in normal A and Am/Fm stars
• HERMES spectroscopy of normal A and Am stars
• An Investigation of Four Chemically Peculiar Stars with Photometric Periods below 12 Hours
• An observer's view on the future of asteroseismology
• A study of Variability of the Marginal Am star HD 176843 observed in the Kepler field