Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Periods of magnetic field variations in the Ap star $\gamma$ Equulei (HD
  201601)   This paper presents a series of 95 new measurements of the longitudinal
(effective) magnetic field $B_e$ of the Ap star $\gamma$ Equ (HD 201601).
Observations were obtained at the coud\'e focus of the 1-m reflector at the
Special Astrophysical Observatory (SAO RAS) in Russia over a time period of
4190 days (more than 11 years). We compiled a long record of $B_e$ points,
adding our measurements to all published data. The time series of magnetic data
consists of 395 $B_e$ points extending for 24488 days, or over 67 years.
Various methods of period determination were examined for the case in which the
length of the observed time series is rather short and amounts only to ~69
percent of the period. We argue that the fitting of a sine wave to the observed
$B_e$ points by least squares yields the most reliable period in the case of
$\gamma$ Equ. Therefore, the best period for long-term magnetic variations of
$\gamma$ Equ, and hence the rotational period, is $P_{\rm rot}=35462.5 \pm
1149$ days $= 97.16 \pm 3.15$ years.

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The categories of this paper are: gr-qc
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The categories of this paper are: econ
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The categories of this paper are: funct-an
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The categories of this paper are: q-fin
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The categories of this paper are: hep-lat
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The categories of this paper are: cs
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-th
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The categories of this paper are: supr-con
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The categories of this paper are: patt-sol
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The categories of this paper are: mtrl-th
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The categories of this paper are: bayes-an
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The categories of this paper are: physics
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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: atom-ph