The changing optical and X-ray emission of the dormant γ Cas star HD 45314

@article{rauw2026changing,
  title = {{The changing optical and X-ray emission of the dormant γ Cas star HD 45314}},
  author = {Rauw G. and Nazé Y. and Bryssinck E. and Vollmann W. and Guarro Fló J. and Dupont X. and Smith M. A. and Motch C. and Henry G. W. and Robrade J. and de Bruin A. and Charbonnel S. and Favaro A. and Fricker P. and Garde O. and Gayrard O. and Güssregen S. and Houpert F. and Larsson M. and Leadbeater R. and Lecocq V. and Le Dû P. and Lester T. and Mulato L. and Petit T. and Pomillo R. and Thizy O. and Weil F.},
  journal = {Astronomy \& Astrophysics},
  year = {2026},
  month = oct,
  doi = {10.1051/0004-6361/202660772},
  url = {https://doi.org/10.1051/0004-6361/202660772},
  note = {CC BY 4.0},
}

TY  - JOUR
TI  - The changing optical and X-ray emission of the dormant γ Cas star HD 45314
AU  - Rauw G.
AU  - Nazé Y.
AU  - Bryssinck E.
AU  - Vollmann W.
AU  - Guarro Fló J.
AU  - Dupont X.
AU  - Smith M. A.
AU  - Motch C.
AU  - Henry G. W.
AU  - Robrade J.
AU  - de Bruin A.
AU  - Charbonnel S.
AU  - Favaro A.
AU  - Fricker P.
AU  - Garde O.
AU  - Gayrard O.
AU  - Güssregen S.
AU  - Houpert F.
AU  - Larsson M.
AU  - Leadbeater R.
AU  - Lecocq V.
AU  - Le Dû P.
AU  - Lester T.
AU  - Mulato L.
AU  - Petit T.
AU  - Pomillo R.
AU  - Thizy O.
AU  - Weil F.
PY  - 2026
DA  - 2026/10/24
JO  - Astronomy & Astrophysics
DO  - 10.1051/0004-6361/202660772
UR  - https://doi.org/10.1051/0004-6361/202660772
AB  - Context. γ Cas stars are Oe or Be stars that exhibit bright and hard X-ray emission. HD 45314 belonged to this category, but lost its γ Cas characteristics as its circumstellar disc started to fade away. Aims. The successive steps of the disc dissipation and its subsequent ongoing rebuilding provide insight into the physical processes at work. Methods. The star was monitored in optical spectroscopy, optical photometry, and X-ray spectroscopy to follow its variability on timescales of hours to years. Emission line properties were measured on the spectra and compared with optical brightness and colours. Time series of magnitudes, colours, line equivalent widths, and violet over red peak intensity ratios were analysed with Fourier methods to uncover possible periodicities. Results. For five years, HD 45314 exhibited magnitude and line strength oscillations 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. However, some residual hard emission is observed. Conclusions. HD 45314’s long-term optical variations bear resemblance to 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, HD 45314’s X-ray properties changed dramatically as the disc began 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.
SN  - 0004-6361
SN  - 1432-0746
ER  -