ATEL #8653                                                           ATEL #8653

Title:  An ongoing, record-breaking outburst of the unique symbiotic
                binary MWC 560 = V694 Mon
Author: U. Munari (INAF Padova), G. L. Righetti, S. Dallaporta, S.
                Moretti, M. Graziani, P. Valisa (ANS Collaboration)
Queries:        ulisse.munari@oapd.inaf.it
Posted: 8 Feb 2016; 20:40 UT
Subjects:Optical, Ultra-Violet, X-ray, Cataclysmic Variable, Variables

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.