Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: MOST detects variability on tau Bootis possibly induced by its planetary
  companion   (abridged) There is considerable interest in the possible interaction between
parent stars and giant planetary companions in 51 Peg-type systems. We
demonstrate from MOST satellite photometry and Ca II K line emission that there
has been a persistent, variable region on the surface of tau Boo A which
tracked its giant planetary companion for some 440 planetary revolutions and
lies ~68deg (phi=0.8) in advance of the sub-planetary point. The light curves
are folded on a range of periods centered on the planetary orbital period and
phase dependent variability is quantified by Fourier methods and by the mean
absolute deviation (MAD) of the folded data for both the photometry and the Ca
II K line reversals. The region varies in brightness on the time scale of a
rotation by ~1 mmag. In 2004 it resembled a dark spot of variable depth, while
in 2005 it varied between bright and dark. Over the 123 planetary orbits
spanned by the photometry the variable region detected in 2004 and in 2005 are
synchronised to the planetary orbital period within 0.0015 d. The Ca II K line
in 2001, 2002 and 2003 also shows enhanced K-line variability centered on
phi=0.8, extending coverage to some 440 planetary revolutions. The apparently
constant rotation period of the variable region and its rapid variation make an
explanation in terms of conventional star spots unlikely. The lack of
complementary variability at phi=0.3 and the detection of the variable region
so far in advance of the sub-planetary point excludes tidal excitation, but the
combined photometric and Ca II K line reversal results make a good case for an
active region induced magnetically on the surface of tau Boo A by its planetary
companion.

31
The categories of this paper are: ao-sci
25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
7
The categories of this paper are: hep-th
5
The categories of this paper are: gr-qc
20
The categories of this paper are: acc-phys
18
The categories of this paper are: econ
2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex
3
The categories of this paper are: physics
28
The categories of this paper are: alg-geom
12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
0
The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph
14
The categories of this paper are: math-ph