Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Why do some young cool stars show spot modulation while others do not?   We present far-red, intermediate resolution spectroscopy of 572
photometrically selected, low-mass stars (0.2<M/M_sun<0.7) in the young open
cluster NGC 2516, using the FLAMES spectrograph at the Very Large Telescope.
Precise radial velocities confirm membership for 210 stars that have published
rotation periods from spot-modulated light curves and for another 144 stars in
which periodic modulation could not be found. The two sub-samples are compared
and no significant differences are found between their positions in
colour-magnitude diagrams, the distribution of their projected equatorial
velocities or their levels of chromospheric activity. We rule out differing
observational sensitivity as an explanation and conclude that otherwise similar
objects, with equally high levels of chromospheric activity, do not exhibit
spot-induced light curve modulation because their significant spot coverage is
highly axisymmetric. We propose that the spot coverage consists of large
numbers of small, dark spots with diameters of about 2 degrees. This explains
why about half of cluster members do not exhibit rotationally modulated light
curves and why the light curve amplitudes of those that do have mean values of
only 0.01-0.02 mag.

15
The categories of this paper are: nucl-ex
31
The categories of this paper are: ao-sci
4
The categories of this paper are: cond-mat
27
The categories of this paper are: comp-gas
21
The categories of this paper are: adap-org
22
The categories of this paper are: chao-dyn
8
The categories of this paper are: hep-ex
0
The categories of this paper are: hep-ph
9
The categories of this paper are: nlin
7
The categories of this paper are: hep-th
25
The categories of this paper are: patt-sol
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: funct-an
30
The categories of this paper are: q-alg