1999/04/30 by A. V. Filippenko, Alexei V. Filippenko, D. C. Leonard +9 · 4 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Scientific Research and Discoveries #astro-ph
paper · pdf · doi:10.1086/316413
16 pages, 9 figures, added references, revised per. referee's comments Accepted for publication in August 1999 issue of PASP
arxiv created 1999/05/20 · openalex publication_date 1999/08/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/30
We have obtained 17 moderate‐resolution (∼2.5 Å) optical spectra of the Galactic X‐ray Nova Velorum 1993 in quiescence with the Keck II telescope. Cross‐correlation with the spectra of late‐type dwarfs (especially K7–M0) yields excellent radial velocities for the secondary star. The orbital period ( P ) is 0.285206 ± 0.0000014 days, and the semiamplitude (K 2 ) is 475.4 ± 5.9 km s −1 . Our derived mass function, f(M 1 ) = PK 3 2 /2πG = 3.17 ± 0.12 M ⊙ , is close to the conventional absolute limiting mass for a neutron star (∼3.0–3.2 M ⊙ )—but if the orbital inclination i≲80° (given the absences of eclipses), then M 1 ≳4.2–4.4 M ⊙ for nominal secondary‐star masses of 0.5 M ⊙ (M0) to 0.65 M ⊙ (K6). Even if the secondary is quite undermassive (e.g., M 2 = 0.3 M ⊙ ), we derive M 1 ≳3.9 M ⊙ . The primary star is therefore almost certainly a black hole rather than a neutron star. Fits to the wings of the double‐peaked Hα emission line yield approximate radial velocities for the compact primary. The velocity curve has a semiamplitude (K 1 ) of 65.3 ± 7.0 km s −1 , but with a phase offset by 237° (rather than 180°) from that of the secondary star. Under the assumption that the observed semiamplitude reflects the motion of the primary (despite this offset, which is common), the mass ratio q = M 2 /M 1 = K 1 /K 2 = 0.137 ± 0.015, and hence for M 2 = 0.5–0.65 M ⊙ we derive M 1 = 3.64–4.74 M ⊙ . The constraints from q and the mass function yield M 1 = 4.4 M ⊙ and i≈78° if we use a normal K7–K8 secondary (M 2 ≈0.6 M ⊙ ). Indeed, consistency cannot be achieved for M 2 ≲0.59 M ⊙ if the maximum inclination estimate (80°) is correct. An adopted mass M 1 ≈4.4 M ⊙ is significantly below the typical value of ∼7 M ⊙ found for black holes in other low‐mass X‐ray binaries. Keck observations of MXB 1659−29 (V2134 Oph) in quiescence reveal a probable optical counterpart at R = 23.6 ± 0.4 mag. This object recently went into a new X‐ray and optical (R≈18 mag) outburst, after about 21 years of inactivity.