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Originally published in Science Express on 2 October 2008
Science 24 October 2008:
Vol. 322. no. 5901, pp. 560 - 562
DOI: 10.1126/science.1160863
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Reports

A Large Excess in Apparent Solar Oblateness Due to Surface Magnetism

Martin D. Fivian,1* Hugh S. Hudson,1 Robert P. Lin,1,2 H. Jabran Zahid1,3

The shape of the Sun subtly reflects its rotation and internal flows. The surface rotation rate, ~2 kilometers per second at the equator, predicts an oblateness (equator-pole radius difference) of 7.8 milli–arc seconds, or ~0.001%. Observations from the Reuven Ramaty High-Energy Solar Spectroscopic Imager satellite show unexpectedly large flattening, relative to the expectation from surface rotation. This excess is dominated by the quadrupole term and gives a total oblateness of 10.77 ± 0.44 milli–arc seconds. The position of the limb correlates with a sensitive extreme ultraviolet proxy, the 284 angstrom limb brightness. We relate the larger radius values to magnetic elements in the enhanced network and use the correlation to correct for it as a systematic error term in the oblateness measurement. The corrected oblateness of the nonmagnetic Sun is 8.01 ± 0.14 milli–arc seconds, which is near the value expected from rotation.

1 Space Sciences Laboratory, University of California–Berkeley, Berkeley, CA 94720, USA.
2 Physics Department, University of California–Berkeley, Berkeley, CA 94720, USA.
3 Institute for Astronomy, University of Hawaii, Manoa, HI 96822, USA.

* To whom correspondence should be addressed. E-mail: mfivian{at}ssl.berkeley.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Comment on "A Large Excess in Apparent Solar Oblateness Due to Surface Magnetism".
J. R. Kuhn, M. Emilio, and R. Bush (2009)
Science 324, 1143
   Abstract »    Full Text »    PDF »
Response to Comment on "A Large Excess in Apparent Solar Oblateness Due to Surface Magnetism".
M. D. Fivian, H. S. Hudson, R. P. Lin, and H. J. Zahid (2009)
Science 324, 1143
   Abstract »    Full Text »    PDF »


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