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

Fuente: arXiv

Saved in:

Bibliographic Details
Main Authors:	Anastasopoulou, K., Guarcello, M. G., Drake, J. J., Ritchie, B., De Becker, M., Bayo, A., Najarro, F., Negueruela, I., Sciortino, S., Flaccomio, E., Castellanos, R., Albacete-Colombo, J. F., Andersen, M., Damiani, F., Fraschetti, F., Gennaro, M., Gunderson, S. J., Larkin, C. J. K., Mackey, J., Moffat, A. F. J., Pradhan, P., Saracino, S., Stevens, I. R., Weigelt, G.
Format:	Preprint
Published:	2025
Subjects:	High Energy Astrophysical Phenomena Solar and Stellar Astrophysics
Online Access:	Acceder al recurso
Tags:	Add Tag No Tags, Be the first to tag this record!

_version_	1866914028670943232
author	Anastasopoulou, K. Guarcello, M. G. Drake, J. J. Ritchie, B. De Becker, M. Bayo, A. Najarro, F. Negueruela, I. Sciortino, S. Flaccomio, E. Castellanos, R. Albacete-Colombo, J. F. Andersen, M. Damiani, F. Fraschetti, F. Gennaro, M. Gunderson, S. J. Larkin, C. J. K. Mackey, J. Moffat, A. F. J. Pradhan, P. Saracino, S. Stevens, I. R. Weigelt, G.
author_facet	Anastasopoulou, K. Guarcello, M. G. Drake, J. J. Ritchie, B. De Becker, M. Bayo, A. Najarro, F. Negueruela, I. Sciortino, S. Flaccomio, E. Castellanos, R. Albacete-Colombo, J. F. Andersen, M. Damiani, F. Fraschetti, F. Gennaro, M. Gunderson, S. J. Larkin, C. J. K. Mackey, J. Moffat, A. F. J. Pradhan, P. Saracino, S. Stevens, I. R. Weigelt, G.
contents	Supergiant B[e] (sgB[e]) stars are exceptionally rare objects, with only a handful 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. We present the most detailed X-ray study of Wd1-9 to date, using X-rays that pierce through its cocoon with the aim to uncover its nature and evolutionary state. We utilize 36 Chandra observations of Wd1 from the 'Extended Westerlund 1 and 2 Open Clusters Survey' (EWOCS), plus eight archival datasets, totalling 1.1 Ms. This dataset allows investigation of long-term variability and periodicity in Wd1-9, while X-ray colours and spectra are analysed over time to uncover patterns that shed light on its nature. 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 (kT approximately 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. 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.
format	Preprint
id	arxiv_https___arxiv_org_abs_2507_17816
institution	arXiv
publishDate	2025
record_format	arxiv
spellingShingle	EWOCS-IV: 1Ms ACIS Chandra observation of the supergiant B[e] star Wd1-9 Anastasopoulou, K. Guarcello, M. G. Drake, J. J. Ritchie, B. De Becker, M. Bayo, A. Najarro, F. Negueruela, I. Sciortino, S. Flaccomio, E. Castellanos, R. Albacete-Colombo, J. F. Andersen, M. Damiani, F. Fraschetti, F. Gennaro, M. Gunderson, S. J. Larkin, C. J. K. Mackey, J. Moffat, A. F. J. Pradhan, P. Saracino, S. Stevens, I. R. Weigelt, G. High Energy Astrophysical Phenomena Solar and Stellar Astrophysics Supergiant B[e] (sgB[e]) stars are exceptionally rare objects, with only a handful 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. We present the most detailed X-ray study of Wd1-9 to date, using X-rays that pierce through its cocoon with the aim to uncover its nature and evolutionary state. We utilize 36 Chandra observations of Wd1 from the 'Extended Westerlund 1 and 2 Open Clusters Survey' (EWOCS), plus eight archival datasets, totalling 1.1 Ms. This dataset allows investigation of long-term variability and periodicity in Wd1-9, while X-ray colours and spectra are analysed over time to uncover patterns that shed light on its nature. 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 (kT approximately 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. 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.
title	EWOCS-IV: 1Ms ACIS Chandra observation of the supergiant B[e] star Wd1-9
topic	High Energy Astrophysical Phenomena Solar and Stellar Astrophysics
url	https://arxiv.org/abs/2507.17816