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An ongoing, record-breaking outburst of the unique symbiotic binary MWC 560 = V694 Mon

ATel #8653; U. Munari (INAF Padova), G. L. Righetti, S. Dallaporta, S. Moretti, M. Graziani, P. Valisa (ANS Collaboration)
on 8 Feb 2016; 20:40 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)

Subjects: Optical, Ultra-Violet, X-ray, Cataclysmic Variable, Variables

Referred to by ATel #: 8832, 8957

The unique symbiotic binary MWC 560 = V694 Mon is on a steep rise in brightness, about to surpass the record level attained during the last - and much studied - outburst of 1990 (Tomov et al. 1990, Nature 346, 637), the brightest event in the historical light-curve of the object (Leibowitz and Formiggini 2014, AJ 150, 52). At that time MWC 560 attracted special interest by showing deep and broad absorptions, blue-shifted by 6000 km/s and completely detached from corresponding emission lines, as if originating in discrete blobs, ejected from the central star and rapidly accelerated to large velocities. These absorptions have shown considerable variability in intensity, profile and velocity over the years. Our last measurement for February 5.967 UT shows MWC 560 at U=9.29, B=9.25, V=8.88, Rc=8.38, and Ic=7.63. For comparison, the peak brightness in 1990 was reached at B~9.4 and V~9.2 (Mikolajewski et al. 1997, IBVS 4519). On February 5 we also collected spectra on MWC 560, in low resolution with the Asiago 1.22m telescope and in high resolution Echelle mode with the Multi Mode Spectrograph on the Varese 0.61m telescope. On top of an A-type hot continuum (with Balmer continuum in absorption), two types of absorption and two types of emission lines are observed. The absorptions in NaI D1-D2, CaII H-K, HeI 5876, and FeII multiplet 42 are located at -1900 km/s, 200-300 km/s wide, with a round profile and are completely detached from the corresponding emission lines. On the contrary the very strong, wide and box-like shaped Balmer absorptions are contiguous to the corresponding emission lines and extend from -300 to -2800 km/s. In addition to the Balmer lines that have extended wings, with FWZI well in excess of 1000 km/s, there is a forest of hundreds of low ionization emission lines (primarily TiII, CrII, FeII, ScII) which are quite narrow (FWHM~40 km/s) and Gaussian in shape. These sharp metallic lines form externally to the region where the broad absorptions originate, because they are observed even within the broad absorption themselves and where their residual continuum is almost null.