2008/02/29 by Jeffrey M. Silverman, J. M. Silverman, Alexei V. Filippenko +1 · 2 citations
Engineering · Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Black hole (networking) #Doubly ionized oxygen #Emission spectrum #Galaxy #Line (geometry) #Mechanics and Biomechanics Studies #Neutron star #Physics #Radial velocity #Spectral line #Star (game theory) #Star formation #Stars #Stellar mass #Wolf–Rayet star #X-ray binary #astro-ph
paper · pdf · doi:10.1086/588096
4 pages, 4 figures, submitted to ApJL
arxiv created 2008/03/07 · openalex publication_date 2008/04/10 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
IC 10 X-1 is a variable X-ray source in the Local Group starburst galaxy IC 10 whose optical counterpart is a Wolf-Rayet (WR) star. Prestwich and coworkers recently proposed that it contains the most massive known stellar-mass black hole (23-34 M ☉ ), but their conclusion was based on radial velocities derived from only a few optical spectra, the most important of which was seriously affected by a CCD defect. Here we present new spectra of the WR star, spanning 1 month, obtained with the Keck I 10 m telescope. The spectra show a periodic shift in the He II λ 4686 emission line as compared with IC 10 nebular lines such as [O III] λ 5007. From this, we calculate a period of 34.93 ± 0.04 hr (consistent with the X-ray period of 34.40 ± 0.83 hr reported by Prestwich) and a radial velocity semiamplitude of 370 ± 20 km s −1 . The resulting mass function is 7.64 ± 1.26 M ☉ , consistent with that of Prestwich (7.8 M ☉ ). This, combined with the previously estimated (from spectra) mass of 35 M ☉ for the WR star, yields a minimum primary mass of 32.7 ± 2.6 M ☉ . Even if the WR star has a mass of only 17 M ☉ , the minimum primary mass is 23.1 ± 2.1 M ☉ . Thus, IC 10 X-1 is indeed a WR/black-hole binary containing the most massive known stellar-mass black hole.