Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The quest for stable circumbinary companions to post-common envelope sdB
  eclipsing binaries Does the observational evidence support their existence?   Context. Period variations have been detected in a number of eclipsing close
compact binary subdwarf B stars (sdBs) and these have often been interpreted as
caused by circumbinary massive planets or brown dwarfs. Various evolutionary
scenarios have been proposed for these stars, but a definite mechanism remains
to be established. Equally puzzling is the formation of these putative
circumbinary objects which must have formed either from the remaining post
common envelope circumbinary disk or survived its evolution. Aims. In this
paper we review the eclipse time variations (ETVs) exhibited by seven such
systems and explore if there is conclusive evidence that the ETVs observed over
the last two decades can reliably predict the presence of circumbinary bodies.
Methods. We report 246 new observations of the seven sdB systems made between
2013 September and 2017 July using a worldwide network of telescopes. We
combined our new data with previously published measurements to analyse the
ETVs of these systems. Results. Our data shows that period variations cannot be
modelled simply on the basis of circumbinary objects. This implies that more
complex processes may be taking place in these systems. From eclipse time
variations, it has historically been suggested that five of the seven binary
systems reported herein had circumbinary objects. Based on our recent
observations and analysis only three systems remain serious contenders. We find
agreement with other observers that at least a decade of observations is
required to establish reliable ephemeris. With longer observational baselines
it is quite conceivable that the data will support the circumbinary object
hypothesis of these binary systems. Also we generally agree with other
observers that larger values of (O-C) residuals are found with secondary
companions of spectral type M5/6 or earlier as a result of an Applegate type
mechanism

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The categories of this paper are: eess
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The categories of this paper are: math-ph
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The categories of this paper are: hep-th
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The categories of this paper are: stat
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The categories of this paper are: q-alg
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The categories of this paper are: plasm-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: supr-con
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The categories of this paper are: hep-ex
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The categories of this paper are: nlin
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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: quant-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-lat