Rapid spectral change in the symbiotic binary V694 Mon (MWC 560)
ATel #15061; V. P. Goranskij (SAI, Moscow Univ. & SAO RAS), A. V. Zharova (SAI, Moscow Univ.), E. A. Barsukova, A. N. Burenkov (SAO RAS)
on 24 Nov 2021; 15:53 UT
Credential Certification: Vitaly Goranskij (goray@sai.msu.ru)
Subjects: Binary, Star, Variables
V694 Mon was a symbiotic binary forming high-velocity jets, showing high-amplitude flickering, and regular outbursts with the period of 1930 days. Munari et al. (2016, New Astronomy V.49, 43) discovered periodic 331 day variations in the Ic band where the radiation of the M giant dominates. In November 2018, the star had the outburst, which did not match the predicted time. At the outburst, the jets disappeared, and flickering stopped until recently (ATel #12227, #14239, #14988). We continue photometric and spectroscopic observations, which show gradual brightening of the system and weakening of the emission lines in the spectrum. The burst predicted with the period of 1930 days should have happened in summer 2021 during the invisibility of the system due to conjunction with the Sun, but this burst did not take place. However, in the middle of October, we recorded the brightness jump by 0.3 mag in all filters. Then the star has broken the record of its brightness in optical bands again. We obtained the spectrum on 2021 October 22.112 UT with the 1 m Zeiss telescope and UAGS spectrograph within the range of 5760-7160 A, the resolution was 2.3 A. The spectrum showed strong absorptions of Si II 6347 and 6371 A characteristic of A type stars, and deep Na I 5891, 5896 A lines. H alpha emission was strong with the narrow absorption component. There were a few weak emissions associated with the Fe II ions. The blue spectrum taken on 2021 November 22.037 UT with the same telescope and device in the range of 3931-5340 A with the resolution of 1.7 A is full absorption spectrum with deep hydrogen absorptions typical of early subtype A stars and multiple Fe II lines now in absorption. We treat the described phenomenon as the transit of the system from the disk accretion to the common envelope configuration with filling the Roche lobe of compact companion. Here, the M giant, the donor star is accreting in the dynamical mode (predicted by Philipp Podsiadlowski). Now, the gainer of accretion material has formed a photosphere like that one of early subtype A star, which cannot excite the surrounding gas shell.
Comparison of V694 Mon spectra in the blue region of early 2018 and late 2021
