Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observational constraints on the magnetic field of RR Lyrae stars   A high percentage of the astrophysically important RR Lyrae stars show a
periodic amplitude and/or phase modulation of their pulsation cycles. More than
a century after its discovery, this "Blazhko effect" still lacks acceptable
theoretical understanding. In one of the plausible models for explaining the
phenomenon, the modulation is caused by the effects of a magnetic field. So
far, the available observational data have not allowed us to either support nor
rule out the presence of a magnetic field in RR Lyrae stars. We intend to
determine whether RR Lyrae stars are generally characterized by the presence of
a magnetic field organized on a large scale. With the help of the FORS1
instrument at the ESO VLT we performed a spectropolarimetric survey of 17
relatively bright southern RR Lyrae stars, both Blazhko stars and non-modulated
stars, and determined their mean longitudinal magnetic field with a typical
error bar < 30 G. All our measurements of the mean longitudinal magnetic field
resulted in null detections within 3 sigma. From our data we can set an upper
limit for the strength of the dipole component of the magnetic fields of RR
Lyrae stars to ~ 130 G. Because of the limitations intrinsic to the diagnostic
technique, we cannot exclude the presence of higher order multipolar
components. The outcome of this survey clarifies that the Blazhko modulation in
the pulsation of RR Lyrae stars is not correlated with the presence of a
strong, quasi-dipolar magnetic field.

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The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
35
The categories of this paper are: mtrl-th
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
4
The categories of this paper are: cond-mat
0
The categories of this paper are: hep-ph
10
The categories of this paper are: q-bio
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The categories of this paper are: nucl-ex
5
The categories of this paper are: gr-qc
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The categories of this paper are: chao-dyn
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The categories of this paper are: quant-ph
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The categories of this paper are: acc-phys
11
The categories of this paper are: hep-lat
28
The categories of this paper are: alg-geom
2
The categories of this paper are: math