Letter to the Editor

Discovery of collimated ejection from the symbiotic binary BF Cygni^⋆

¹ Astronomical Institute, Slovak Academy of Sciences, 059 60 Tatranská Lomnica, Slovakia
e-mail: skopal@astro.sk
² Institute of Astronomy and NAO, Bulgarian Academy of Sciences, PO Box 136, 4700 Smolyan, Bulgaria

Received: 2 January 2013
Accepted: 29 January 2013

Abstract

Context. Detection of collimated ejection from white dwarfs (WD) in symbiotic binaries is very rare and has employed a variety of methods in X-ray, radio, optical imagery, and spectroscopy. To date, its signature in the optical spectra has only been recorded for four objects (MWC 560, Hen 3-1341, StHα 190, and Z And).

Aims. We present the first observational evidence of highly-collimated bipolar ejection from the symbiotic binary BF Cyg, which developed during its current (2006-12) active phase, and determine their physical parameters.

Methods. We monitored the outburst with the optical high-resolution spectroscopy and multicolour UBVR_CI_C photometry.

Results. During 2009, three years after the 2006-eruption of BF Cyg, satellite components to Hα and Hβ lines emerged in the spectrum. During 2012, they became stable and were located symmetrically with respect to the main emission core of the line. Spectral properties of these components suggest bipolar ejection collimated within an opening angle of  ≲15°, whose radiation is produced by an optically thin medium with the emission measure of 1−2 × 10⁵⁹   (d/3.8   kpc)² cm^-3.

Conclusions. Formation of the collimated ejection a few years after the eruption and its evolution on a time scale of years at a constant optical brightness can aid us in better understanding the accretion process during the active phases of symbiotic stars.