Shape of a slowly rotating star measured by asteroseismology

Laurent Gizon, Takashi Sekii, Masao Takata, Donald W. Kurtz, Hiromoto Shibahashi, Michael Bazot, Othman Benomar, Aaron C. Birch, Katepalli R. Sreenivasan

Research output: Contribution to journalArticle


Stars are not perfectly spherically symmetric. They are deformed by rotation and magnetic fields. Until now, the study of stellar shapes has only been possible with optical interferometry for a few of the fastest-rotating nearby stars. We report an asteroseismic measurement, with much better precision than interferometry, of the asphericity of an A-type star with a rotation period of 100 days. Using the fact that different modes of oscillation probe different stellar latitudes, we infer a tiny but significant flattening of the star's shape of DR/R = (1.8 ± 0.6) × 10-6. For a stellar radius R that is 2.24 times the solar radius, the difference in radius between the equator and the poles is DR = 3 ± 1 km. Because the observed DR/R is only one-third of the expected rotational oblateness, we conjecture the presence of a weak magnetic field on a star that does not have an extended convective envelope. This calls to question the origin of the magnetic field.

Original languageEnglish (US)
Article numbere1601777
JournalScience Advances
Issue number11
StatePublished - Nov 2016

ASJC Scopus subject areas

  • General

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    Gizon, L., Sekii, T., Takata, M., Kurtz, D. W., Shibahashi, H., Bazot, M., Benomar, O., Birch, A. C., & Sreenivasan, K. R. (2016). Shape of a slowly rotating star measured by asteroseismology. Science Advances, 2(11), [e1601777].