Psi Cassiopeiae
An orange-hued evolved giant binary in Cassiopeia.
Psi Cassiopeiae, also known by the Bayer designation ψ Cas or Psi Cas, is a binary star system found in the northern constellation Cassiopeia. The two stars together shine at a combined apparent visual magnitude of +4.72, making them just bright enough to spot without a telescope. Parallax measurements place the system about 201 light-years (62 parsecs) from Earth, and it is moving toward the Sun at a radial velocity of −13 km/s.
The primary star, ψ Cassiopeiae A, has an apparent magnitude of +5.0 and an orange hue. It is itself a double star, cataloged as CCDM J01259+6808AB, with a faint 14th-magnitude companion located about 3 arcseconds away. About 25 arcseconds farther out lies an optical companion, CCDM J01259+6808CD, which older star catalogs labeled ψ Cassiopeiae B. This companion is also a double, consisting of a 9.4-magnitude star (component C) and a 10th-magnitude star (component D).
The primary is an evolved K-type giant with a stellar classification of K0 III-IIIb CN0.5, indicating a mild overabundance of the CN molecule. It is a red clump giant, meaning it sits on the horizontal branch of its evolutionary path. Estimated to be 5.2 billion years old, it has about 2.5 times the Sun’s mass and has expanded to 11 times the Sun’s radius. Its photosphere radiates 44 times the Sun’s luminosity at an effective temperature of 4,442 K.
- Combined apparent magnitude
- +4.72
- Distance
- 201 light-years (62 pc)
- Parallax
- 16.24 mas
- Radial velocity
- −13 km/s
- Primary spectral type
- K0 III-IIIb CN0.5
- Primary apparent magnitude
- +5.0
- Primary mass
- 2.5 solar masses
- Primary radius
- 11 solar radii
- Primary luminosity
- 44 solar luminosities
- Primary effective temperature
- 4,442 K
Lore & Background
The orange-hued primary component, ψ Cassiopeiae A, has an apparent magnitude of +5.0; it is a double star, designated CCDM J01259+6808AB, with a fourteenth magnitude star (component B) located 3 arcseconds from the primary. Located about 25 arcseconds distant there is a 9.8 magnitude optical companion CCDM J01259+6808CD, designated ψ Cassiopeiae B in older star catalogues, which is itself another double; CD comprises a 9.4 magnitude component C and a 10 magnitude component D.
The primary has a stellar classification of K0 III-IIIb CN0.5, which presents as an evolved K-type giant star. The suffix notation indicates a mild overabundance of the CN molecule. It is a red clump giant, indicating it is on the horizontal branch of its evolutionary track. At an estimated age of 5.2 billion years, it has 2.5 times the mass of the Sun and has expanded to 11 times the Sun's radius. It is radiating 44 times the luminosity of the Sun from its photosphere at an effective temperature of 4,442 K.
Reader's Guide
Psi Cassiopeiae is notable as a multiple-star system that includes a red clump giant primary, a type of evolved star on the horizontal branch. Its combined magnitude of +4.72 makes it visible without optical aid, and its distance of about 201 light-years places it within the solar neighborhood. The system's radial velocity of −13 km/s indicates it is moving toward the Sun. The primary's classification as K0 III-IIIb CN0.5 with a mild overabundance of the CN molecule provides insight into its chemical peculiarity. The presence of multiple visual companions—a 14th-magnitude star at 3 arcseconds and a 9.8-magnitude optical double at 25 arcseconds—adds to its interest as a hierarchical multiple system. The primary's age of 5.2 billion years, mass of 2.5 solar masses, and radius of 11 solar radii offer a snapshot of stellar evolution in the red clump phase. The system's legacy lies in its use as a benchmark for studying evolved giants and multiple-star dynamics in the Cassiopeia constellation.
Did You Know?
- The primary is a red clump giant on the horizontal branch of its evolutionary track.
- The system has a combined apparent visual magnitude of +4.72, visible to the naked eye.
- The primary has a mild overabundance of the CN molecule, indicated by the suffix CN0.5.
- The system includes an optical companion that is itself a double star, designated CCDM J01259+6808CD.
More in Binary and Multiple Stars, Part 3 1-24
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