Comprehensive UV and Optical spectral analysis of Cygnus X-1: Stellar and wind parameters, abundances, and evolutionary implications
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| Main Authors: | , , , , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866912397135970304 |
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| author | Ramachandran, V. Sander, A. A. C. Oskinova, L. M. Schoesser, E. C. Pauli, D. Hamann, W. -R. Mahy, L. Bernini-Peron, M. Brigitte, M. Kubátová, B. |
| author_facet | Ramachandran, V. Sander, A. A. C. Oskinova, L. M. Schoesser, E. C. Pauli, D. Hamann, W. -R. Mahy, L. Bernini-Peron, M. Brigitte, M. Kubátová, B. |
| contents | We present a comprehensive analysis of Cyg X-1, utilizing archival high-resolution UV and optical spectra in conjunction with sophisticated atmospheric models. Notably, this is the first investigation to simultaneously analyze UV and optical spectra of Cyg X-1 along with incorporating X-rays to constrain the stellar and wind parameters. Our analysis yields notably lower masses for both the donor (29$\,M_\odot$) and the black hole (12.7 to 17.8$\,M_\odot$, depending on inclination), and confirms that the donor's radius is close to reaching the inner Lagrangian point. We find super-solar Fe, Si, and Mg abundances (1.3-1.8 times solar) at the surface of the donor star, while the total CNO abundance remains solar despite evidence of CNO processing (N enrichment, O depletion) and He enrichment. This abundance pattern is distinct from the surrounding Cyg OB3 association. We observe a clear difference in wind parameters between X-ray states: $v_\infty \approx 1200\,\mathrm{km\,s}^{-1}$ and $\dot{M} \approx 3\times 10^{-7}\,M_\odot\,\mathrm{yr}^{-1}$ in the high/soft state, increasing to $v_\infty\lesssim 1800\,\mathrm{km\,s}^{-1}$ and $\dot{M}\lesssim 5\times 10^{-7}\,M_\odot\,\mathrm{yr}^{-1}$ in the low/hard state. The observed X-ray luminosity is consistent with wind-fed accretion. Evolutionary models show that Cyg X-1 will undergo Roche lobe overflow in the near future. Under a fully conservative mass accretion scenario, our models predict a future binary black hole merger for Cyg X-1 within $\sim5$ Gyr. Our comprehensive analysis provides refined stellar and wind parameters of the donor star in Cyg X-1, highlighting the importance of using advanced atmospheric models and considering X-ray ionization and wind clumping. The observed abundances suggest a complex formation history involving a high initial metallicity. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2504_05885 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Comprehensive UV and Optical spectral analysis of Cygnus X-1: Stellar and wind parameters, abundances, and evolutionary implications Ramachandran, V. Sander, A. A. C. Oskinova, L. M. Schoesser, E. C. Pauli, D. Hamann, W. -R. Mahy, L. Bernini-Peron, M. Brigitte, M. Kubátová, B. Solar and Stellar Astrophysics High Energy Astrophysical Phenomena We present a comprehensive analysis of Cyg X-1, utilizing archival high-resolution UV and optical spectra in conjunction with sophisticated atmospheric models. Notably, this is the first investigation to simultaneously analyze UV and optical spectra of Cyg X-1 along with incorporating X-rays to constrain the stellar and wind parameters. Our analysis yields notably lower masses for both the donor (29$\,M_\odot$) and the black hole (12.7 to 17.8$\,M_\odot$, depending on inclination), and confirms that the donor's radius is close to reaching the inner Lagrangian point. We find super-solar Fe, Si, and Mg abundances (1.3-1.8 times solar) at the surface of the donor star, while the total CNO abundance remains solar despite evidence of CNO processing (N enrichment, O depletion) and He enrichment. This abundance pattern is distinct from the surrounding Cyg OB3 association. We observe a clear difference in wind parameters between X-ray states: $v_\infty \approx 1200\,\mathrm{km\,s}^{-1}$ and $\dot{M} \approx 3\times 10^{-7}\,M_\odot\,\mathrm{yr}^{-1}$ in the high/soft state, increasing to $v_\infty\lesssim 1800\,\mathrm{km\,s}^{-1}$ and $\dot{M}\lesssim 5\times 10^{-7}\,M_\odot\,\mathrm{yr}^{-1}$ in the low/hard state. The observed X-ray luminosity is consistent with wind-fed accretion. Evolutionary models show that Cyg X-1 will undergo Roche lobe overflow in the near future. Under a fully conservative mass accretion scenario, our models predict a future binary black hole merger for Cyg X-1 within $\sim5$ Gyr. Our comprehensive analysis provides refined stellar and wind parameters of the donor star in Cyg X-1, highlighting the importance of using advanced atmospheric models and considering X-ray ionization and wind clumping. The observed abundances suggest a complex formation history involving a high initial metallicity. |
| title | Comprehensive UV and Optical spectral analysis of Cygnus X-1: Stellar and wind parameters, abundances, and evolutionary implications |
| topic | Solar and Stellar Astrophysics High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2504.05885 |