# pi Aqr is another gamma-Cas object

## TL;DR

This paper confirms pi Aqr as a gamma-Cas object with unique binary characteristics, supporting a disk-related origin for gamma-Cas phenomena over accretion models.

## Contribution

It identifies pi Aqr as another gamma-Cas star with a known stellar companion, challenging the accretion hypothesis for gamma-Cas phenomena.

## Key findings

- pi Aqr exhibits gamma-Cas-like X-ray properties.
- The companion to pi Aqr is a non-degenerate star, not a compact object.
- The small separation challenges accretion-based explanations.

## Abstract

The gamma-Cas category is a subgroup of Be stars displaying a strong, hard, and variable thermal X-ray emission. An XMM-Newton observation of pi Aqr reveals spectral and temporal characteristics that clearly make this Be star another member of the gamma-Cas category. Furthermore, pi Aqr is a binary but, contrary to gamma-Cas, the nature of the companion to the Be star is known; it is a non-degenerate (stellar) object and its small separation from the Be star does not leave much room for a putative compact object close to the Be disk. This renders the accretion scenario difficult to apply in this system, and, hence, this discovery favors a disk-related origin for the gamma-Cas phenomenon.