| Issue |
A&A
Volume 701, September 2025
|
|
|---|---|---|
| Article Number | A67 | |
| Number of page(s) | 16 | |
| Section | Stellar atmospheres | |
| DOI | https://doi.org/10.1051/0004-6361/202555544 | |
| Published online | 02 September 2025 | |
The multi-faceted variability of HD 192639
Stochastic behaviour, regularities, and an exceptional mass-ejection event★
Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège,
Allée du 6 Août, 19c, Bât B5c,
4000
Liège,
Belgium
★★ Corresponding author: g.rauw@uliege.be
Received:
16
May
2025
Accepted:
9
July
2025
Aims. Spectroscopic and photometric variability is widespread among O-type supergiants. It is linked to various phenomena affecting the star and its circumstellar environment, thereby providing direct information concerning them. To investigate such connections, we decided to revisit the prototypical O7.5 Iabf supergiant HD 192639.
Methods. High-cadence spectroscopic monitoring was performed simultaneously with intensive space-borne photometric observations. The data were analysed with several methods to characterise the variability.
Results. Besides the usual stochastic, low-frequency photometric variability, our observations reveal the presence of recurrent –but transient– modulations on a timescale of about five days. The same signal is present in the spectroscopic data and was already seen two decades ago. This stability suggests that this timescale corresponds to the stellar rotation. Furthermore, our observations unveil, for the first time, an unusually strong dimming event in the light curve associated with absorption and emission changes in HI and He I lines. This unprecedented trough corresponds to an episodic ejection of a rather large amount of mass (its column density being comparable to that of the steady wind). While rare, such an event could hint at an overlooked aspect of mass loss in massive stars.
Key words: stars: early-type / stars: massive / stars: individual: HD 192639 / stars: variables: general
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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