Sigma Cassiopeiae

Not to be confused with S Cassiopeiae.

Sigma Cassiopeiae is a binary star^[5] system in the northern constellation of Cassiopeia. Its name is a Bayer designation that is Latinized from σ Cassiopeiae, and abbreviated Sigma Cas or σ Cas. The pair have a combined apparent magnitude of +4.88,^[10] making it visible to the naked eye. Based on Parallax measurements, it is located at a distance of 1,200 to 1,400 light years from Earth.

σ Cassiopeiae

Location of σ Cassiopeiae (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Cassiopeia
σ Cas A
Right ascension	23h 59m 00.538s[1]
Declination	+55° 45′ 17.75″[1]
Apparent magnitude (V)	5.01[2]
σ Cas B
Right ascension	23h 59m 00.331s[3]
Declination	+55° 45′ 20.37″[3]
Apparent magnitude (V)	7.24[2]
Characteristics
σ Cas A
Spectral type	B2 IV[4]
U−B color index	−0.82
B−V color index	−0.07
Variable type	β Cep[5][6]
σ Cas B
Spectral type	B3 V[4]
Astrometry
σ Cas A
Radial velocity (Rv)	−12.6[7] km/s
Proper motion (μ)	RA: +9.956[1] mas/yr Dec.: −4.492[1] mas/yr
Parallax (π)	2.7419±0.1491 mas[1]
Distance	1,190 ± 60 ly (360 ± 20 pc)
Absolute magnitude (MV)	−3.90[5]
Radial velocity (Rv)	−5.0[7] km/s
Proper motion (μ)	RA: +8.651[3] mas/yr Dec.: −3.739[3] mas/yr
Parallax (π)	2.2572±0.0558 mas[3]
Distance	1,440 ± 40 ly (440 ± 10 pc)
Absolute magnitude (MV)	−1.7[4]
Details[5]
A
Mass	12 M☉
Radius	11.3 R☉
Luminosity	25,000 L☉
Surface gravity (log g)	3.6 cgs
Temperature	21,000 K
Rotational velocity (v sin i)	170 km/s
Age	15.8 Myr
Other designations
σ Cas, 8 Cassiopeiae, BD+54°3082, HD 224572, HIP 118243, HR 9071, SAO 35947, ADS 17140, CCDM J23591+5546[8]
Database references
SIMBAD	data
	A
	B

σ Cassiopeiae in optical light

Light curves for Sigma Cassiopeiae, plotted from TESS data.^[9]

The primary component, σ Cassiopeiae A, has an apparent magnitude of +5.01 and presents as a subgiant star with a stellar classification of B2 IV.^[4] It is a candidate Beta Cephei variable and is rotating rapidly.^[5] Its companion, σ Cassiopeiae B, is a main sequence dwarf with a class of B3 V^[4] and an apparent magnitude of +7.14. The two stars are three arcseconds apart.^[11]

Naming

In Chinese, 螣蛇 (Téng Shé), meaning Flying Serpent, refers to an asterism consisting of σ Cassiopeiae, α Lacertae, 4 Lacertae, π² Cygni, π¹ Cygni, HD 206267, ε Cephei, β Lacertae, ρ Cassiopeiae, τ Cassiopeiae, AR Cassiopeiae, 9 Lacertae, 3 Andromedae, 7 Andromedae, 8 Andromedae, λ Andromedae, κ Andromedae, ι Andromedae, and ψ Andromedae. Consequently, the Chinese name for σ Cassiopeiae itself is 螣蛇十一 (Téng Shé shíyī, English: the Eleventh Star of Flying Serpent).^[12]