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Is there a propeller neutron star in Cas?
Cas is the prototype of a small population of B0-B1.5 III-V
classical Be (cBe) stars that emit anomalous and hard X-rays with a unique
array of properties. Cas is known to host, like other cBe stars, a
decretion disk and also a low mass companion. Recently Postnov et al. have
posited that this companion is a magnetized rapidly spinning neutron star that
deflects direct gravitational accretion from a stellar/disk wind via the
"propeller mechanism." These authors state that the key X-ray observations are
"remarkably well produced" in this scenario. We reexamine this mechanism in
detail and conclude that there are a number of fatal objections in its
application to the Cas case. Among other considerations these issues
include the prediction under the propeller scenario of a much smaller
population of Cas stars than is observed and the lack of allowance for
observed correlations of X-ray and UV and/or optical properties over a variety
of timescales.Comment: 9 page
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