Shape of a slowly rotating star measured by asteroseismology
| Autor: | Gizon, Laurent, Sekii, Takashi, Takata, Masao, Kurtz, Donald W., Shibahashi, Hiromoto, Bazot, Michael, Benomar, Othman, Birch, Aaron C., Sreenivasan, Katepalli R. |
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| Rok vydání: | 2016 |
| Předmět: | |
| Zdroj: | Science Advances 16 Nov 2016, Vol. 2, no. 11, e1601777 |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1126/sciadv.1601777 |
| Popis: | 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 $\Delta R/R = (1.8 \pm 0.6) \times 10^{-6}$. For a stellar radius $R$ that is $2.24$ times the solar radius, the difference in radius between the equator and the poles is $\Delta R = 3 \pm 1$ km. Because the observed $\Delta R/R$ 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. Comment: 15 pages, 2 tables, 3 figures |
| Databáze: | arXiv |
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