Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Preponderance of Perpendicular Planets   Observing the Rossiter-McLaughlin effect during a planetary transit allows
the determination of the angle $\lambda$ between the sky projections of the
star's spin axis and the planet's orbital axis. Such observations have revealed
a large population of well-aligned systems and a smaller population of
misaligned systems, with values of $\lambda$ ranging up to 180$^\circ$. For a
subset of 57 systems, we can now go beyond the sky projection and determine the
3-d obliquity $\psi$ by combining the Rossiter-McLaughlin data with constraints
on the line-of-sight inclination of the spin axis. Here we show that the
misaligned systems do not span the full range of obliquities; they show a
preference for nearly-perpendicular orbits ($\psi=80-125^\circ$) that seems
unlikely to be a statistical fluke. If confirmed by further observations, this
pile-up of polar orbits is a clue about the unknown processes of obliquity
excitation and evolution.

21
The categories of this paper are: adap-org
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The categories of this paper are: econ
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The categories of this paper are: patt-sol
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The categories of this paper are: eess
4
The categories of this paper are: cond-mat
12
The categories of this paper are: nucl-th
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The categories of this paper are: ao-sci
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-ex
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The categories of this paper are: q-fin
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-lat
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The categories of this paper are: solv-int
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The categories of this paper are: chem-ph
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The categories of this paper are: q-alg
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The categories of this paper are: supr-con