Toward Understanding the B[e] Phenomenon. IX. Nature and Binarity of MWC645
Miroshnichenko, A. S.; Manset, N.; Zharikov, S. V.; Larionov, V. M.; Arkharov, A. A.; Grankin, K. N.; Rudy, R. J.; Klochkova, V. G.; Omarov, C. T.; Khokhlov, S. A.; Puetter, R. C.; Efimova, N.; Klimanov, S.; Kokumbaeva, R. I.; Reva, I. V.; Perry, R. B.; Nodyarov, A. S.
Kazakhstan, United States, Russia, Mexico
Abstract
We present the results of optical and near-IR spectroscopy and multicolor photometry of the emission-line star MWC 645, which exhibits the B[e] phenomenon. The presence of positionally variable absorption lines of a cool star detected for the first time indicates that the object is a binary system. Using a combination of the photometric and spectroscopic data as well as the Gaia EDR3 distance (D = 6.5 ± 0.9 kpc), we disentangled the components' contributions and estimated their surface temperatures and luminosities (18, 000 ± 2000 K and 4250 ± 250 K, log L/L ⊙ = 4.0 ± 0.5 and 3.1 ± 0.3 for the hot and cool components, respectively). Quasi-cyclic short-period (months) and long-period (~4 yr) photometric variations were detected in both optical and near-IR regions, and are most likely due to variable circumstellar extinction. Our analysis suggests that MWC 645 is a member of the FS CMa group. The object's properties can be described by an evolutionary model of a close binary system that currently undergoes a nonconservative mass transfer between intermediate-mass stars (e.g., 7 M ⊙ + 2.8 M ⊙).