CH Cygni

Not to be confused with Chi Cygni.

CH Cygni (CH Cyg / HIP 95413 / BD +49 2999) is a red giant, variable, symbiotic binary in the constellation Cygnus.

CH Cygni

Location of CH Cygni (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Cygnus
Right ascension	19h 24m 33.06773s[1]
Declination	+50° 14′ 29.1263″[1]
Apparent magnitude (V)	5.60 – 8.49[2]
Characteristics
Spectral type	M7IIIab + Be[3]
Variable type	Z And and SR[2]
Astrometry
Radial velocity (Rv)	−59.74[4] km/s
Proper motion (μ)	RA: −7.09[1] mas/yr Dec.: −59.74[1] mas/yr
Parallax (π)	5.4642±0.2172 mas[5]
Distance	600 ± 20 ly (183 ± 7 pc)
Orbit[6]
Period (P)	15.58±0.13 yr
Semi-major axis (a)	8.5 AU
Eccentricity (e)	0.122±0.024
Inclination (i)	84°
Semi-amplitude (K1) (primary)	4.45±0.12 km/s
Details[6]
Red giant
Mass	2 M☉
Radius	280 R☉
Luminosity	5012 L☉
Temperature	3,100 K
White dwarf
Mass	0.7 M☉
Luminosity	0.25 L☉
Other designations
HD 182917, BD+49°2999, HIP 95413, SAO 31632
Database references
SIMBAD	data

Properties

CH Cygni has a mass of 2 M_☉ and a radius of 280 R_☉. Its white-dwarf companion has a mass of 0.75 M_☉, and the orbital period of the two stars is 5689 days.^[6] CH Cygni is classified as M7IIIab + Be.^[3]

Observation history

A blue band light curve for CH Cygni, adapted from Wallerstein et al. (2010)^[7]

The earliest observations of CH Cygni were made in 1890 by Pickering and Wendel using wedge photometer, and was classified as a M6III variable star in 1924.^[8] In 1963 strong H I emissions were observed, indicating CH Cygni was likely in a symbiotic relationship with a white dwarf. Similar emissions were observed in 1965, 1967, 1977, 1992, and 1998.^[9] The system was briefly thought to contain a third star^[10] but this was later disproved.^[6]

In 1984 bipolar jets were detected coming from CH Cygni, which were suspected to be due to accretion from its companion star.^[9][8] The luminosity of the system decreased significantly in 1986, likely owing to dust thrown out of the system by the jets or a concurrent helium flash. This dust had dissipated by 2002, with subsequent luminosities returning to pre-1985 levels.^[3]