Sigma Cassiopeiae
A binary star system in Cassiopeia, visible to the naked eye.
Sigma Cassiopeiae, also known by its Bayer designation σ Cassiopeiae (abbreviated Sigma Cas or σ Cas), is a binary star system located in the northern constellation Cassiopeia. The combined apparent magnitude of the pair is +4.88, which is bright enough to be seen without a telescope. Parallax measurements place the system roughly 1,200 parsecs from Earth.
The primary star, σ Cassiopeiae A, has an apparent magnitude of +5.01 and is classified as a B2 IV subgiant. It is a candidate Beta Cephei variable and rotates rapidly. Its companion, σ Cassiopeiae B, is a B3 V main-sequence dwarf with an apparent magnitude of +7.14. The two stars are separated by about three arcseconds.
In Chinese astronomy, the star is part of an asterism called Flying Serpent, which also includes 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. The Chinese name for σ Cassiopeiae itself is derived from this asterism.
- Bayer designation
- σ Cassiopeiae
- Combined apparent magnitude
- +4.88
- Distance
- 1,200 parsecs
- Primary component
- σ Cassiopeiae A
- Primary apparent magnitude
- +5.01
- Primary spectral type
- B2 IV
- Primary classification
- subgiant star, candidate Beta Cephei variable
- Secondary component
- σ Cassiopeiae B
- Secondary apparent magnitude
- +7.14
- Secondary spectral type
- B3 V
Lore & Background
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. It is a candidate Beta Cephei variable and is rotating rapidly. Its companion, σ Cassiopeiae B, is a main sequence dwarf with a class of B3 V and an apparent magnitude of +7.14. The two stars are three arcseconds apart. In Chinese astronomy, the asterism known as Flying Serpent includes σ Cassiopeiae along with many other stars, and the Chinese name for σ Cassiopeiae itself is derived from that asterism.
Reader's Guide
Sigma Cassiopeiae is notable as a binary system whose primary is a candidate Beta Cephei variable, a class of pulsating stars important for studying stellar structure and evolution. The rapid rotation of the primary adds interest for investigations of stellar rotation and its effects on spectral lines and variability. The system's combined magnitude of +4.88 makes it accessible to naked-eye observers, while the 3-arcsecond separation of the two components allows them to be resolved with modest telescopes. The primary's subgiant classification (B2 IV) indicates it has begun to evolve away from the main sequence, offering a glimpse into the later stages of massive star development. The secondary, a main sequence B3 V dwarf, provides a contrast in evolutionary state. The system's inclusion in the Chinese Flying Serpent asterism ties it to a rich cultural tradition of celestial mapping.
Did You Know?
- Sigma Cassiopeiae has a combined apparent magnitude of +4.88, visible to the naked eye.
- The two stars are separated by three arcseconds.
- The system is part of the Chinese Flying Serpent asterism.
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