Symbiotic BF Cygni in deep eclipse
Posted: Sat Jul 25, 2026 5:33 pm
The symbiotic system BF Cyg is in eclipse
Spectra are welcome for studies and inclusion in the database:
https://aras-database.github.io/database/bfcyg.html
BF Cygni is an eclipsing symbiotic binary system consisting of a cool M-type giant and
a hot white dwarf (WD) companion. The system has an orbital period of approximately
757.2 days (Fekel2001). The red giant is classified roughly as spectral type M3–M5 III
. The white dwarf accretes material from the wind of the giant, producing a hot and
luminous source with effective temperatures estimated to range from 40 to 95 kK dur-
ing quiescence, though the temperature can be lower during outbursts (Kenyon1984,
Skopal2005, McKeever2011).
The system exhibits complex photometric and spectroscopic behavior characterized by
alternating quiescent and active phases. The active phases include outbursts with bright-
ness increases of up to several magnitudes and are accompanied by enhanced mass outflow
from the hot component. These outflows manifest as P Cygni profiles and high-velocity
satellite emission components in Balmer lines, indicating bipolar collimated jets with
velocities of a few hundred to several thousand km.s−1 (Shchurova 2019, Skopal 2013, Mc-
Keever 2011, Tomova 2025).
The historical light curve of BF Cyg shows a symbiotic nova-like outburst around 1895,
followed by several Z And-type outbursts and short-term orbitally modulated flares (Lei-
bowitz 2006). During active phases, a cool, optically thick pseudophotosphere or disk-like
envelope forms around the white dwarf, which can collimate stellar wind into bipolar jets
(Tomov 2019). The depth and shape of the orbital eclipses vary with the activity level,
reflecting changes in the geometry and structure of the emitting regions.
Spectral observations reveal a rich emission line spectrum dominated by low-ionization
species during outbursts, with occasional disappearance of highly ionized emission lines
such as He II and [Fe III] (McKeever 2011).
- BFCyg_BV_2012-2025.png (37.7 KiB) Viewed 15 times
- bfcyg_echelle_5RV2026-07-23.png (66.46 KiB) Viewed 15 times
https://aras-database.github.io/database/bfcyg.html
BF Cygni is an eclipsing symbiotic binary system consisting of a cool M-type giant and
a hot white dwarf (WD) companion. The system has an orbital period of approximately
757.2 days (Fekel2001). The red giant is classified roughly as spectral type M3–M5 III
. The white dwarf accretes material from the wind of the giant, producing a hot and
luminous source with effective temperatures estimated to range from 40 to 95 kK dur-
ing quiescence, though the temperature can be lower during outbursts (Kenyon1984,
Skopal2005, McKeever2011).
The system exhibits complex photometric and spectroscopic behavior characterized by
alternating quiescent and active phases. The active phases include outbursts with bright-
ness increases of up to several magnitudes and are accompanied by enhanced mass outflow
from the hot component. These outflows manifest as P Cygni profiles and high-velocity
satellite emission components in Balmer lines, indicating bipolar collimated jets with
velocities of a few hundred to several thousand km.s−1 (Shchurova 2019, Skopal 2013, Mc-
Keever 2011, Tomova 2025).
The historical light curve of BF Cyg shows a symbiotic nova-like outburst around 1895,
followed by several Z And-type outbursts and short-term orbitally modulated flares (Lei-
bowitz 2006). During active phases, a cool, optically thick pseudophotosphere or disk-like
envelope forms around the white dwarf, which can collimate stellar wind into bipolar jets
(Tomov 2019). The depth and shape of the orbital eclipses vary with the activity level,
reflecting changes in the geometry and structure of the emitting regions.
Spectral observations reveal a rich emission line spectrum dominated by low-ionization
species during outbursts, with occasional disappearance of highly ionized emission lines
such as He II and [Fe III] (McKeever 2011).