%0 Journal Article
%A Gizon, Laurent
%A Sekii, Takashi
%A Takata, Masao
%A Kurtz, Donald W.
%A Shibahashi, Hiromoto
%A Bazot, Michael
%A Benomar, Othman
%A Birch, Aaron C.
%A Sreenivasan, Katepalli R.
%T Shape of a slowly rotating star measured by asteroseismology
%D 2016
%R 10.1126/sciadv.1601777
%J Science Advances
%P e1601777
%V 2
%N 11
%X 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 ΔR/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 ΔR = 3 ± 1 km. Because the observed ΔR/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.
%U https://advances.sciencemag.org/content/advances/2/11/e1601777.full.pdf