Discovery of collimated ejection from the symbiotic binary BF Cygni

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 C I 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 × 10 59 (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.

Symbiotic stars with spectral indication of bipolar ejection and stellar wind

“…This gives us a reason to suppose that they are related to the same individual line component which appears in absorption at some stage of the outburst but changes into emission afterwards. The transformation of the absorption into emission is seen in the spectrum of 2011 Septem- satellite Hα and Hβ emission components with a velocity of about ±400 km s −1 are analyzed with a Gaussian function to determine their exact wavelength position and equivalent width in the paper by Skopal et al (2013). During the 2006-2013 outburst of BF Cyg the satellite line components indicating a collimated ejection were observed for the first time in this system.…”

“…We observed the regions of the Hα and Hβ lines of BF Cyg on seven nights during 2009 June -2012 September (Skopal et al 2013). During the whole time of the observations the Hα line had a multicomponent profile: a central narrow emission which occasionally was double with a blueshifted central reversal and very broad wings of low intensity and extending to a velocity of about ±2200 km s −1 from the center of the line (Fig.…”

“…12). Based on both a comparison with Hβ and an analysis of the line profiles (Skopal et al 2013), we assume that the Hα peaks/bumps with radial velocity of ∼ 400 km s −1 indicate a bipolar collimated outflow from the outbursting component of the system.…”

“…Five of all symbiotic systems with collimated outflow have an optical indication by additional satellite emission/absorption components of their spectral lines. These systems are MWC 560 (Tomov et al 1990), Hen 3 -1341 (Tomov et al 2000), StHα 190 (Munari et al 2001, Z And (Burmeister & Leedjarv 2007;Tomov, Tomova & Bisikalo 2007), and BF Cyg (Skopal, Tomov & Tomova 2013). In four of these systems, excepting MWC 560, a bipolar outflow was observed during phases of activity when an additional P Cyg absorption, indicating a stellar wind from the outbursting compact object, was observed along with the satellite line components.…”

“…Corresponding author: tomov@astro.bas.bg are low and do not contribute to the jet velocity. Observations, however, show that in many of the stars with an optical indication of a collimated outflow (Z And, Hen 3 -1341, StHα 190, BF Cyg), this indication is present in the spectrum only during their active state when a non-collimated loss of mass by the outbursting white dwarf is realised, too (Skopal et al 2009;Tomov et al 2012;Tomov et al 2000;Munari et al 2001;Munari et al 2005;Skopal et al 2013;Skopal, private communication). That suggests to us that the two kinds of outflow are probably connected and the collimated outflow occurs only along with the non-collimated one.…”