Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Measurement of Spin-Orbit Alignment in an Extrasolar Planetary System   We determine the stellar, planetary, and orbital properties of the transiting
planetary system HD 209458, through a joint analysis of high-precision radial
velocities, photometry, and timing of the secondary eclipse. Of primary
interest is the strong detection of the Rossiter-McLaughlin effect, the
alteration of photospheric line profiles that occurs because the planet occults
part of the rotating surface of the star. We develop a new technique for
modeling this effect, and use it to determine the inclination of the planetary
orbit relative to the apparent stellar equator [lambda = (-4.4 +/- 1.4)
degrees], and the line-of-sight rotation speed of the star [v*sin(I) = (4.70
+/- 0.16) km/s]. The uncertainty in these quantities has been reduced by an
order of magnitude relative to the pioneering measurements by Queloz and
collaborators. The small but nonzero misalignment is probably a relic of the
planet formation epoch, because the expected timescale for tidal
coplanarization is larger than the age of the star. Our determination of
v*sin(I) is a rare case in which rotational line broadening has been isolated
from other broadening mechanisms.

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The categories of this paper are: physics
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The categories of this paper are: hep-ex
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The categories of this paper are: solv-int
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The categories of this paper are: dg-ga
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The categories of this paper are: stat
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The categories of this paper are: acc-phys
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The categories of this paper are: atom-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: q-bio
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The categories of this paper are: chem-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: cond-mat
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
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The categories of this paper are: gr-qc
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The categories of this paper are: math