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 journalArticlepeer-review


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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