Toward Understanding the B[e] Phenomenon. VII. AS 386, a Single-lined Binary with a Candidate Black Hole Component
Reichart, D. E.; Miroshnichenko, A. S.; Manset, N.; Zharikov, S. V.; Larionov, V. M.; Arkharov, A. A.; Caton, D. B.; Rudy, R. J.; Haislip, J. B.; Kuratova, A. K.; Khokhlov, S. A.; Agishev, A.; Chojnowski, S. D.; Kouprianov, V. V.; Smith, A. B.; Puetter, R. C.; Efimova, N.; Klimanov, S.; Kusakin, A. V.; Kokumbaeva, R. I.; Perry, R. B.; Kuratov, K. S.; Omarov, Ch. T.; Laag, E. A.; Crawford, K. B.; Swift, T. K.; Hawkins, R. L.
Kazakhstan, United States, Mexico, Russia
Abstract
We report the results of spectroscopic and photometric observations of the emission-line object AS 386. For the first time we found that it exhibits the B[e] phenomenon and fits the definition of an FS CMa type object. The optical spectrum shows the presence of a B-type star with the following properties: T eff = 11,000 ± 500 K, log L/L ⊙ = 3.7 ± 0.3, a mass of 7 ± 1 M ⊙, and a distance D = 2.4 ± 0.3 kpc from the Sun. We detected regular radial velocity variations of both absorption and emission lines with the following orbital parameters: P orb =131.27 ± 0.09 days, semiamplitude K 1 = 51.7 ± 3.0 km s-1, systemic radial velocity γ = -31.8 ± 2.6 km s-1, and a mass function of f(m) = 1.9 ± 0.3 M ⊙. AS 386 exhibits irregular variations of the optical brightness (V = 10.92 ± 0.05 mag), while the near-IR brightness varies up to ∼0.3 mag following the spectroscopic period. We explain this behavior by a variable illumination of the dusty disk inner rim by the B-type component. Doppler tomography based on the orbital variations of emission-line profiles shows that the material is distributed near the B-type component and in a circumbinary disk. We conclude that the system has undergone a strong mass transfer that created the circumstellar material and increased the B-type component mass. The absence of any traces of a secondary component, whose mass should be ≥7 M ⊙, suggests that it is most likely a black hole.