High-Dispersion Spectroscopy of BF Cygni at the Beginning of the 2006 Outburst

BF Cygni (hereafter BF Cyg) is a symbiotic star that in 2006 July started into an optical outburst that has lasted for several years. Between 2006 August and 2007 January we obtained high-dispersion spectra (r ∼ 35,000) over the wavelength range of 3800-10000 Å of BF Cyg with the 3.5 m echelle spectrograph at Apache Point Observatory. The emission lines in the optical spectrum of BF Cyg changed dramatically during the interval of observations. The species found were mostly low-ionization emission lines of H, He, C, N, O, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, and Ni. Both permitted and forbidden lines were seen. In particular, Fe I was observed in emission, which is not a common phenomenon. We discuss the evolution of the BF Cyg spectrum during the 5 month interval of our observations. Some emission lines developed P-Cygni profiles indicating gas expanding at about 100-200 km s^-1. Other lines changed from emission to absorption. A few absorption lines that had not been observed in 2006 August were evident on the spectra obtained in 2006 November and 2007 January. Some interesting (but unidentified) persistent broad features were observed in the continuum. Comparisons of our observations with previous spectroscopy of BF Cyg demonstrate that the emission spectrum is in a lower state of excitation during this outburst than during quiescence.