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THE ASTRONOMER Electronic Circular No 3057      2015 Feb 03 20.48UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK      Backup: gmh@wdcc1.bnsc.rl.ac.uk
WORLD WIDE WEB                         http://www.theastronomer.org
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BF CYGNI
U. Munari (INAF Padova) et. al., report on ATEL 7013 that the symbiotic nova
BF Cyg was discovered when it erupted in 1894 peaking at B=9.7.  It remained
close to maximum for 30 years, and starting with 1924 it begun a slow and
gradual descent toward quiescence when, in August 2006 while passing through
B=13.0, it suddenly erupted again (Munari et al.  2006, CBET 596), reaching
initially B=10.3 and later peaking at B=9.7 in October 2008. 
It has remained around maximum ever since, with the light-curve nicely
modulated by the 757 day orbital period. 

They are intensively monitoring BF Cyg since 2005, both spectroscopically
and photometrically.  On top the protracted maximum, now lasting for more
than 8 years, an unexpected large amplitude and fast evolving flare has
recently developed. It started between 2014 Nov 22, when we measured BF Cyg
at B=11.15, V=10.47, Rc=9.64, Ic=8.82, and 2014 Dec 21 when BF was already
at B=10.72, V=9.98, Rc=9.30, Ic=8.55. According to their observations, the
peak brightness occurred around 26 January 2015 at B=9.95, V=9.44, Rc=9.03,
Ic=8.45. 

The spectra largely changed in response to the flare. We obtained    
Echelle spectra of BF Cyg with the Varese 0.61m telescope on 2014 Aug 7
(pre-flare) and 2015 Jan 28 (flare peak), and with the Asiago 1.82m
telescope of 2015 Jan 6 (flare rise).  Low resolution spectra were obtained
with the Asiago 1.22m on 2014 Nov 18 (pre-flare), 2014 Dec 26 (flare rise)
and 2015 Jan 31 (flare peak).  Pre-flare spectra were dominated by very
strong Balmer continuum and lines in emission, and strong and sharp HeI
lines with no P-Cyg associated absorption.  During the flare rise, HeI and
NaI lines broadened and developed strong P-Cyg absorptions with terminal
velocities around -250 km/sec.  At flare maximum, HeI lines and higher
Balmer lines turned into pure absorptions, with only Halpha and Hbeta
remaining in emission, and among the great number of weak FeII and other low
excitation emission lines, only FeII multiplet 42 lines retained a weak
P-Cyg absorption component. No high velocity jet feature has appeared in the
emission line profiles. 

Guy M Hurst