Multicolour photometry and Echelle spectroscopy of the symbiotic star BF Cyg during its 2014-15 large flare

ATel #7258; A. Skopal, M. Sekeras, S. Shugarov, T. Pribulla, M. Vanko (Astronomical Institute, Slovak Academy of Sciences, Tatranska Lomnica)
on 20 Mar 2015; 13:21 UT
Credential Certification: Augustin Skopal (skopal@ta3.sk)

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We report on the current high-level activity of the classical symbiotic star BF Cyg during its 2014-15 large flare (see ATel #7013). Our recent (U)BVRcIc CCD photometric measurements (2015 January 6.674 UT: U=9.83, B=10.27, V=9.72, Rc=9.12, Ic=8.34; February 16.184 UT: B=9.74, V=9.36, Rc=8.91, Ic=8.25) and UBV photoelectric photometry (2014 December 4.685 UT: U=10.36, B=11.05, V=10.46; 2015 February 7.166 UT: U=9.65, B=10.04, V=9.62; February 18.135 UT: U=9.42, B=9.78, V=9.43; March 17.130 UT: U=9.53, B=9.87, V=9.50 and March 18.073 UT: U=9.58, B=9.88, V=9.48) taken at the observatories of the Astronomical Institute of the Slovak Academy of Sciences confirmed the 2014-15 large brightening of BF Cyg as reported by Munari et al. (ATel #7013). Our multicolour photometry reflects a continuing activity of BF Cyg at a high level around its historical maximum. It is of interest to note that a 1.5-hour monitoring of BF Cyg in the B band, carried out on March 8, did not show any rapid variability to within of a few hundredths of magnitude.

On 2015 February 15.177 UT, 18.180 UT, March 10.140 UT, 11.126 UT, 19.121 UT and 20.121, we obtained Echelle medium-resolution spectra of BF Cyg (R ~ 11000) with our 0.6 m telescope (pavilion G1). The continuum profile (420 - 715 nm) dereddened with E(B-V)=0.35 mag was comparable with a stellar photosphere radiating at 7000 - 10000 K. The line spectrum was dominated by hydrogen lines. Their profiles were characterized with the central sharp absorption located at ~ -27 km/s, accompanied with the blueward deep and broad absorption terminating at ~ -550 km/s. Simultaneously, a strong emission bump with the terminal velocity of ~ +550 km/s developed at the red side of the emission line core. Similar type of the line profile was observed for the strongest FeII lines. Example of the H-alpha and H-beta line profiles from 2015 March 11 is available at http://www.ta3.sk/~astrskop/atel_032015/bf_hab.png . Such evolution can be interpreted in terms of a biconically collimated mass-outflow at its early stage (see Skopal et al., 2013, A&A, 551, L10). Our work was supported by grants of the Slovak Academy of Sciences VEGA No. 2/0002/13 and 2/0143/14.

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