The changing optical and X-ray emission of the dormant γ Cas star HD 45314
Abstract
γ Cas stars are Oe/Be stars that exhibit bright and hard X-ray emission. HD45314 belonged to this category, but lost its γ Cas characteristics as its circumstellar disc started to fade away. The star was monitored in optical spectroscopy, optical photometry, and X-ray spectroscopy to follow its variability on timescales of hours to years. Time series of magnitudes, colours, line equivalent widths and violet over red peak intensity ratios were analysed with Fourier methods to uncover possible periodicities. For five years, HD45314 exhibited oscillations of its magnitude and line strengths on a timescale of 230 d. It then declined towards a nearly disc-free stage and is now slowly rebuilding its disc. During these phases, the violet over red peak intensity ratio exhibited a modulation on a timescale of about 1190 d. Over the whole campaign, prominent short-term photometric variations, notably at a frequency of 3.369 d−1, were probably due to β Cep-type pulsations. The amplitude of these pulsations was stronger during phases of overall brightness changes. In parallel, the X-ray spectrum switched to a low state at the onset of the oscillation phase and has remained in this low state since then. Some residual hard emission is nonetheless observed. HD45314's long-term optical variations bear resemblance with the predictions of smooth particle hydrodynamics calculations, although a close look does reveal some inconsistencies. Unlike some other γ Cas stars, where the X-ray emission remained nearly constant despite major changes of the circumstellar disc, HD45314's X-ray properties changed dramatically as the disc begun to dissipate. These differences might arise from a wider orbital separation between the Oe star and its putative white dwarf companion or from the ablation of the disc by the radiation field of the Oe star.
Related
- Star formation powers optical line emission from the CGM
- Coherent radio emission at 45 MHz from the nearby planet-hosting star GJ 725A
- Radio and high-energy variable emission from a multi-wavelength follow-up study of the infant planet-hosting star V1298,Tau
- The Emergence of X-Ray Emission Lines during Relativistic Radio-jet Formation in the Changing-look Active Galactic Nucleus 1ES 1927+654
- Evolutionary Map of the Universe (EMU): Selection of active galactic nuclei and star-formation emission with machine-learning techniques
BibTeX
@misc{rauw2026changing,
title = {{The changing optical and X-ray emission of the dormant $γ$ Cas star HD 45314}},
author = {G. Rauw and Y. Nazé and E. Bryssinck and W. Vollmann and J. Guarro Fló and X. Dupont and M. A. Smith and C. Motch and G. W. Henry and J. Robrade and A. de Bruin and S. Charbonnel and A. Favaro and P. Fricker and O. Garde and O. Gayrard and S. Güssregen and F. Houpert and M. Larsson and R. Leadbeater and V. Lecocq and P. Le Dû and T. Lester and L. Mulato and T. Petit and R. Pomillo and O. Thizy and F. Weil},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.09780},
eprint = {2609.09780},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.09780},
}
RIS
TY - UNPB
TI - The changing optical and X-ray emission of the dormant γ Cas star HD 45314
AU - G. Rauw
AU - Y. Nazé
AU - E. Bryssinck
AU - W. Vollmann
AU - J. Guarro Fló
AU - X. Dupont
AU - M. A. Smith
AU - C. Motch
AU - G. W. Henry
AU - J. Robrade
AU - A. de Bruin
AU - S. Charbonnel
AU - A. Favaro
AU - P. Fricker
AU - O. Garde
AU - O. Gayrard
AU - S. Güssregen
AU - F. Houpert
AU - M. Larsson
AU - R. Leadbeater
AU - V. Lecocq
AU - P. Le Dû
AU - T. Lester
AU - L. Mulato
AU - T. Petit
AU - R. Pomillo
AU - O. Thizy
AU - F. Weil
PY - 2026
DA - 2026/09/09
PB - arXiv
DO - 10.48550/arxiv.2609.09780
UR - https://arxiv.org/abs/2609.09780
AB - γ Cas stars are Oe/Be stars that exhibit bright and hard X-ray emission. HD45314 belonged to this category, but lost its γ Cas characteristics as its circumstellar disc started to fade away. The star was monitored in optical spectroscopy, optical photometry, and X-ray spectroscopy to follow its variability on timescales of hours to years. Time series of magnitudes, colours, line equivalent widths and violet over red peak intensity ratios were analysed with Fourier methods to uncover possible periodicities. For five years, HD45314 exhibited oscillations of its magnitude and line strengths on a timescale of 230 d. It then declined towards a nearly disc-free stage and is now slowly rebuilding its disc. During these phases, the violet over red peak intensity ratio exhibited a modulation on a timescale of about 1190 d. Over the whole campaign, prominent short-term photometric variations, notably at a frequency of 3.369 d^−1, were probably due to β Cep-type pulsations. The amplitude of these pulsations was stronger during phases of overall brightness changes. In parallel, the X-ray spectrum switched to a low state at the onset of the oscillation phase and has remained in this low state since then. Some residual hard emission is nonetheless observed. HD45314's long-term optical variations bear resemblance with the predictions of smooth particle hydrodynamics calculations, although a close look does reveal some inconsistencies. Unlike some other γ Cas stars, where the X-ray emission remained nearly constant despite major changes of the circumstellar disc, HD45314's X-ray properties changed dramatically as the disc begun to dissipate. These differences might arise from a wider orbital separation between the Oe star and its putative white dwarf companion or from the ablation of the disc by the radiation field of the Oe star.
ER -