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EWOCS-IV: 1 Ms ACIS Chandra observation of the supergiant B(e) star Wd1-9

Context. Supergiant B[e] (sgB[e]) stars are exceptionally rare objects, with only a select number of confirmed examples in the Milky Way. The evolutionary pathways leading to the sgB[e] phase remain largely debated, highlighting the need for additional observations. The sgB[e] star Wd1-9, located in...

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Hauptverfasser: Anastasopoulou, Konstantina (VerfasserIn) , Guarcello, M. G. (VerfasserIn) , Drake, J. J. (VerfasserIn) , Ritchie, B. (VerfasserIn) , Becker, M. De (VerfasserIn) , Bayo, A. (VerfasserIn) , Najarro, F. (VerfasserIn) , Negueruela, I. (VerfasserIn) , Sciortino, S. (VerfasserIn) , Flaccomio, E. (VerfasserIn) , Castellanos, R. (VerfasserIn) , Albacete-Colombo, J. F. (VerfasserIn) , Andersen, M. (VerfasserIn) , Damiani, F. (VerfasserIn) , Fraschetti, F. (VerfasserIn) , Gennaro, M. (VerfasserIn) , Gunderson, S. J. (VerfasserIn) , Larkin, Cormac (VerfasserIn) , Mackey, J. (VerfasserIn) , Moffat, A. F. J. (VerfasserIn) , Pradhan, P. (VerfasserIn) , Saracino, S. (VerfasserIn) , Stevens, I. R. (VerfasserIn) , Weigelt, G. (VerfasserIn)
Dokumenttyp: Article (Journal)
Sprache:Englisch
Veröffentlicht: 09 September 2025
In: Astronomy and astrophysics
Year: 2025, Jahrgang: 701, Pages: 1-16
ISSN:1432-0746
DOI:10.1051/0004-6361/202555305
Online-Zugang:Verlag, kostenfrei, Volltext: https://doi.org/10.1051/0004-6361/202555305
Verlag, kostenfrei, Volltext: https://www.aanda.org/articles/aa/abs/2025/09/aa55305-25/aa55305-25.html
Volltext
Verfasserangaben:K. Anastasopoulou, M.G. Guarcello, J.J. Drake, B. Ritchie, M. De Becker, A. Bayo, F. Najarro, I. Negueruela, S. Sciortino, E. Flaccomio, R. Castellanos, J.F. Albacete-Colombo, M. Andersen, F. Damiani, F. Fraschetti, M. Gennaro, S.J. Gunderson, C.J.K. Larkin, J. Mackey, A.F. J. Moffat, P. Pradhan, S. Saracino, I.R. Stevens, and G. Weigelt
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Zusammenfassung:Context. Supergiant B[e] (sgB[e]) stars are exceptionally rare objects, with only a select number of confirmed examples in the Milky Way. The evolutionary pathways leading to the sgB[e] phase remain largely debated, highlighting the need for additional observations. The sgB[e] star Wd1-9, located in the massive cluster Westerlund 1 (Wd1), is enshrouded in a dusty cocoon - likely the result of past eruptive activity - leaving its true nature enigmatic. Aims. We present the most detailed X-ray study of Wd1-9 to date, using X-rays that pierce through its cocoon with the aim of uncovering its nature and evolutionary state. Methods. We utilised 36 Chandra observations of Wd1 from the ‘Extended Westerlund 1 and 2 Open Clusters Survey’ (EWOCS), plus eight archival datasets, totalling 1.1 Ms. We used this dataset to investigate long-term variability and periodicity in Wd1-9, and analysed X-ray colours and spectra over time to uncover patterns that shed light on its nature. Results. Wd1-9 exhibits significant long-term X-ray variability, within which we identify a strong ∼14-day periodic signal. We interpret this as the orbital period, marking the first period determination for the system. The X-ray spectrum of Wd1-9 is thermal and hard (T ∼ 3.0 keV), resembling the spectra of bright Wolf-Rayet (WR) binaries in Wd1, while a strong Fe emission line at 6.7 keV indicates hot plasma from a colliding-wind X-ray binary. Conclusions. Wd1-9, with evidence of past mass loss, circumbinary material, a hard X-ray spectrum, and a newly detected 14-day period, displays all the hallmarks of a binary - likely a WR+OB - that recently underwent early Case B mass transfer. Its sgB[e] classification is likely phenomenological, reflecting emission from the dense circumbinary material. This places Wd1-9 in a rarely observed phase, possibly revealing a newly formed WN star, bridging the gap between immediate precursors and later evolutionary stages in Wd1.
Beschreibung:Gesehen am 05.02.2026
Beschreibung:Online Resource
ISSN:1432-0746
DOI:10.1051/0004-6361/202555305

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