Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical and X-ray variability of two Small Magellanic Cloud X-ray binary
  pulsars - SXP46.6 and SXP6.85   We present long-term optical and RXTE data of two X-ray binary pulsars in the
Small Magellanic Cloud, SXP46.6 and SXP6.85. The optical light curves of both
sources show substantial (~0.5-0.8 mag) changes over the time span of the
observations. While the optical data for SXP6.85 do not reveal any periodic
behaviour, by detrending the optical measurements for SXP46.6 we find an
orbital period of ~137 days, consistent with results from the X-ray data. The
detection of Type I X-ray outbursts from SXP46.6, combined with the fact that
we also see optical outbursts at these times, implies that SXP46.6 is a high
orbital eccentricity system. Using contemporaneous optical spectra of SXP46.6
we find that the equivalent width of the H_alpha emission line changes over
time indicating that the size of the circumstellar disc varies. By studying the
history of the colour variations for SXP6.85 we find that the source gets
redder as it brightens which can also be attributed to changes in the
circumstellar disc. We do not find any correlation between the X-ray and
optical data for SXP6.85. The results for SXP6.85 suggest that it is a low
eccentricity binary and that the optical modulations are due to the Be
phenomenon.

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The categories of this paper are: q-bio
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The categories of this paper are: math-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: chao-dyn
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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: plasm-ph
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The categories of this paper are: alg-geom
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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: eess
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The categories of this paper are: hep-th
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The categories of this paper are: nlin
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The categories of this paper are: ao-sci
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The categories of this paper are: supr-con
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The categories of this paper are: chem-ph