Chandra HETG X-Ray Spectra and Variability of π Aqr, a γ Cas-type Be Star

Abstract

High-resolution X-ray spectra of π Aqr, a γ Cas-type star, obtained with the Chandra/HETG spectrometer, revealed emission lines of H-like ions of Mg, Si, S, and Fe; a strong, hard continuum; and a lack of He-like ions, indicating the presence of very hot thermal plasma. The X-ray light curve showed significant fluctuations, with coherent variability at a period of about 3400 s in one observation. The hardness ratio was relatively constant except for one observation in which the spectrum was much harder and more absorbed. We interpret the X-ray emission as arising from accretion onto the secondary, which is likely a magnetic white dwarf, an intermediate polar system.

Keywords

• X-ray astronomy
• Gamma Cassiopeiae stars
• High resolution spectroscopy
• Early-type emission stars
• White dwarf stars
• Be stars