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|Title:||Spots on Am stars||Authors:||Balona, L. A.
Abedigamba, O. P.
|Issue Date:||2015||Journal:||MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY||Number:||448||Issue:||2||First Page:||1378||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.||Acknowledgments:||This paper includes data collected by the Kepler mission. Funding for the Kepler mission is provided by the NASA Science Mission directorate. The authors wish to thank the Kepler team for their generosity in allowing the data to be released and for their outstanding efforts which have made these results possible. Much of the data presented in this paper were obtained from the MAST. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. LAB wishes to thank the South African Astronomical Observatory and the National Research Foundation for financial support.||URI:||http://hdl.handle.net/20.500.12386/25924||URL:||https://academic.oup.com/mnras/article/448/2/1378/1058607||ISSN:||0035-8711||DOI:||10.1093/mnras/stv076||Bibcode ADS:||2015MNRAS.448.1378B||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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