H_alpha observations of the Be/X-ray binary MWC 656
Abstract
Context. MWC 656 is a Be/X-ray binary identified as an emission-line object, X-ray and radio source and might be a weak gamma-ray source, harbouring an enigmatic secondary component. Aims. Our aim here is to study the orbital modulation of the H-alpha emission line, disc truncation and to evaluate the binary parameters. Methods. During the period 2021-2026, we obtained high resolution (30000) optical spectra of MWC 656 and analysed them together with the published data. Results. We find an orbital modulation of the H_alpha emission line with period P orb = 60.43 +/- 0.03 d. By assuming that the Be circumstellar disc is truncated by the companion, we estimate orbital eccentricity e = 0.11 +/- 0.01, semimajor axis a=160 R_sun, and mass of the binary M_1 + M_2 = 15.1 M_sun. Conclusions. The orbital modulation of the H_alpha emission suggests that (1) in this object we have a new type of cyclic variability of a Be disc; (2) the orbit is mildly eccentric; and (3) the secondary component of MWC 656 is a massive object 5 M_sun, more massive than the neutron stars - a stellar-mass black hole or a massive stripped star.
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BibTeX
@misc{zamanov2026halpha,
title = {{H_alpha observations of the Be/X-ray binary MWC 656}},
author = {R. Zamanov and V. Marchev and K. A. Stoyanov and M. D. Christova and M. Minev and M. Moyseev and D. Marchev and J. Marti and M. F. Bode and P. Markishki and S. Stefanov},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.27500},
eprint = {2609.27500},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.27500},
}
RIS
TY - UNPB
TI - H_alpha observations of the Be/X-ray binary MWC 656
AU - R. Zamanov
AU - V. Marchev
AU - K. A. Stoyanov
AU - M. D. Christova
AU - M. Minev
AU - M. Moyseev
AU - D. Marchev
AU - J. Marti
AU - M. F. Bode
AU - P. Markishki
AU - S. Stefanov
PY - 2026
DA - 2026/09/23
PB - arXiv
DO - 10.48550/arxiv.2609.27500
UR - https://arxiv.org/abs/2609.27500
AB - Context. MWC 656 is a Be/X-ray binary identified as an emission-line object, X-ray and radio source and might be a weak gamma-ray source, harbouring an enigmatic secondary component. Aims. Our aim here is to study the orbital modulation of the H-alpha emission line, disc truncation and to evaluate the binary parameters. Methods. During the period 2021-2026, we obtained high resolution (30000) optical spectra of MWC 656 and analysed them together with the published data. Results. We find an orbital modulation of the H_alpha emission line with period P orb = 60.43 +/- 0.03 d. By assuming that the Be circumstellar disc is truncated by the companion, we estimate orbital eccentricity e = 0.11 +/- 0.01, semimajor axis a=160 R_sun, and mass of the binary M_1 + M_2 = 15.1 M_sun. Conclusions. The orbital modulation of the H_alpha emission suggests that (1) in this object we have a new type of cyclic variability of a Be disc; (2) the orbit is mildly eccentric; and (3) the secondary component of MWC 656 is a massive object 5 M_sun, more massive than the neutron stars - a stellar-mass black hole or a massive stripped star.
ER -