# Is there a propeller neutron star in $\gamma$ Cas?

## TL;DR

This paper critically evaluates the hypothesis that a propeller mechanism involving a neutron star explains the unique X-ray emissions of $ ext{γ}$ Cas, finding significant objections to this model.

## Contribution

The paper provides a detailed reexamination of the propeller neutron star hypothesis for $ ext{γ}$ Cas, identifying key issues that challenge its validity.

## Key findings

- The propeller scenario predicts fewer $ ext{γ}$ Cas stars than observed.
- It fails to account for observed X-ray, UV, and optical correlations.
- Major objections undermine the neutron star propeller explanation.

## Abstract

$\gamma$ 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. $\gamma$ 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 $\gamma$ Cas case. Among other considerations these issues include the prediction under the propeller scenario of a much smaller population of $\gamma$ 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.