Comprehensive UV and Optical spectral analysis of Cygnus X-1: Stellar and wind parameters, abundances, and evolutionary implications

Abstract

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: $v_{\infty }\approx 1200{\mathrm{km}\mathrm{s}}^{-1}$ and $\dot{M}\approx 3\times 10^{-7}{M}_{\odot }{\mathrm{yr}}^{-1}$ in the high/soft state, increasing to $v_{\infty }\lesssim 1800{\mathrm{km}\mathrm{s}}^{-1}$ 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 $\sim 5$ 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.

paper is accepted for publication in A&A

References in corpus (25)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Mass loss from hot massive stars
• Present-day cosmic abundances. A comprehensive study of nearby early B-type stars and implications for stellar and Galactic evolution and interstellar dust models
• Cygnus X-1 contains a 21-solar mass black hole -- implications for massive star winds
• Observational constraints on the origin of the elements. IV: The standard composition of the Sun
• On the consistent treatment of the quasi-hydrostatic layers in hot star atmospheres
• The IACOB project: III. New observational clues to understand macroturbulent broadening in massive O- and B-type stars
• The Galactic radial abundance gradients of C, N, O, Ne, S, Cl and Ar from deep spectra of H II regions
• Identifying quiescent compact objects in massive Galactic single-lined spectroscopic binaries
• Stellar Wind Variations During the X-ray High and Low States of Cygnus X-1
• Large Metallicity Variations in the Galactic Interstellar Medium
• Re-estimating the Spin Parameter of the Black Hole in Cygnus X-1
• On the radial abundance gradients of nitrogen and oxygen in the inner Galactic disc
• Empirical mass-loss rates and clumping properties of Galactic early-type O supergiants
• The stellar and wind parameters of six prototypical HMXBs and their evolutionary status
• About Metallicity Variations in the Local Galactic Interstellar Medium
• X-ray emission from BH+O star binaries expected to descend from the observed galactic WR+O binaries
• The IACOB project IX. Building a modern empirical database of Galactic O9-B9 supergiants: sample selection, description, and completeness
• The IACOB project X. Large-scale quantitative spectroscopic analysis of Galactic luminous blue stars
• Phase-resolved spectroscopic analysis of the eclipsing black hole X-ray binary M33 X-7: System properties, accretion, and evolution
• Ultraviolet observations of the X-ray photoionized wind of Cygnus X-1 during X-ray soft/high state
• Optical Spectroscopic Observations of Cyg X-1=HDE 226868
• Formation of Wind-Fed Black Hole High-mass X-ray Binaries: The Role of Roche-lobe-Overflow Post Black-Hole Formation
• Orbital modulations of X-ray light curves of Cyg X-1 in its low/hard and high/soft states
• Extremely iron-poor O-type stars in the Magellanic Bridge

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