2014/01/06 by J. Ziółkowski, Janusz Ziolkowski · 2 citations
Engineering · Physics and Astronomy · #Astrophysical Phenomena and Observations #Mechanics and Biomechanics Studies #Pulsars and Gravitational Waves Research #astro-ph.SR
paper · pdf · doi:10.1093/mnrasl/slu002
accepted for publication in MNRAS
arxiv created 2014/01/06 · openalex publication_date 2014/02/24 · arxiv updated 2014/03/05 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
Abstract A recent determination of the distance to the HDE 226868/Cyg X-1 binary system and a more precise determination of the effective temperature of HDE 226868 allow for a more accurate estimate of the masses of both components. Using up-to-date evolutionary models, I obtain a mass range of between 25 and 35 M⊙ for the mass of the supergiant and between 13 and 23 M⊙ for the mass of the black hole. By accepting more liberal estimates of uncertainties in both the distance and the effective temperature, it is possible to extend these ranges to 21–35 and 10–23 M⊙ for both masses, respectively. The most likely values within these ranges are 27 and 16 M⊙, respectively. The mass obtained for the black hole agrees with the value of 15 ± 1 M⊙ suggested by Orosz et al. However, their value of 19 ± 2 M⊙ suggested for the mass of the supergiant should not be used because such a star violates the mass–luminosity relation for the massive core hydrogen-burning stars. This consideration was not incorporated into the iterative process of Orosz et al. To resolve this violation, I consider the possibility that the hydrogen content of HDE 226868 might be lowered as a result of the mass transfer and the induced fast rotation of the mass gainer. I have analysed the evolutionary effects of such a situation and have found that, while important, these do not invalidate the conclusions listed above. If, as a result of the rotation-induced mixing, the present hydrogen content of HDE 226868 is equal to about 0.6 (as suggested by some observational data), then its present mass might be lower: ∼24 M⊙ rather than ∼27 M⊙.