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Blobrana


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Am stars
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Title: Spots on Am stars
Author: L. A. Balona, G. Catanzaro, O. P. Abedigamba, V. Ripepi, B. Smalley

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.

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Blobrana


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Title: SuperWASP observations of pulsating Am stars
Authors: B Smalley (Keele University), D.W. Kurtz, A.M.S. Smith, L. Fossati, D.R. Anderson, S.C.C. Barros, O.W. Butters, A. Collier Cameron, D.J. Christian, B. Enoch, F. Faedi, C.A. Haswell, C. Hellier, S.Holmes, K. Horne, S.R. Kane, T.A. Lister, P.F.L. Maxted, A.J. Norton, N. Parley, D. Pollacco, E.K. Simpson, I. Skillen, J. Southworth, R.A. Street, R.G. West, P.J. Wheatley, P.L. Wood

We have studied over 1600 Am stars at a photometric precision of 1 mmag with SuperWASP photometric data. Contrary to previous belief, we find that around 200 Am stars are pulsating delta Sct and gamma Dor stars, with low amplitudes that have been missed in previous, less extensive studies. While the amplitudes are generally low, the presence of pulsation in Am stars places a strong constraint on atmospheric convection, and may require the pulsation to be laminar. While some pulsating Am stars have been previously found to be delta Sct stars, the vast majority of Am stars known to pulsate are presented in this paper. They will form the basis of future statistical studies of pulsation in the presence of atomic diffusion.

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Blobrana


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Am star
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An Am star or metallic-line star is a type of chemically peculiar star of spectral type A whose spectrum has strong and often variable absorption lines of metals such as zinc, strontium, zirconium, and barium, and deficiencies of others, such as calcium and scandium. These abnormalities are due to some elements which absorb more light being pushed towards the surface, while others sink under the force of gravity. This effect takes place only if the star has low rotational velocity.
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