Phi Cassiopeiae
A multiple star system in Cassiopeia with two supergiant components.
Phi Cassiopeiae, also known as Phi Cas or φ Cas, is a multiple star system found in the northern constellation Cassiopeia. Its two brightest stars are designated A and C, sometimes called φ1 and φ2 Cas. The system shines with a combined apparent magnitude of +4.95, making it visible without a telescope.
Quick Facts
- Bayer designation
- φ Cassiopeiae
- Combined apparent magnitude
- +4.95
Facts from the source article.
System
Phi Cassiopeiae is found among the stars of the open cluster NGC 457, which lies about 2400 parsecs away, though it is not clear if the star truly belongs to the cluster. The system is usually described as having five components, labeled A through E based on their distance from the brightest star. Components A and C are the two most luminous stars in the NGC 457 field and are sometimes called φ1 and φ2 Cassiopeiae. Component B is a 12th-magnitude star located 49 arcseconds from φ1. Components D and E are both 10th-magnitude B-type main-sequence stars in the same field, with E only 42 arcseconds from φ2. Three additional components are occasionally included in the multiple system, but this is somewhat arbitrary since dozens of NGC 457 members lie within a few arcminutes. The two supergiants, A and C, have a space motion similar to other stars in NGC 457, but their brightness and evolutionary stage make them unlikely members. Their Gaia Data Release 2 parallaxes are similar to those of other cluster stars and match the accepted distance of NGC 457, and component C has a 70 percent chance of being a cluster member.
Properties
The main star in the Phi Cassiopeiae system is a very bright yellow supergiant. Its absolute magnitude rivals that of some yellow hypergiants, but it lacks the extreme mass loss and instability needed to be classified as one. Models consistently show a temperature near 7,300 Kelvin, weak surface gravity, and a huge radius and luminosity. Its mass is less certain; it likely started much heavier but has since shed a lot, with published estimates varying. The system's third component, star C, is a fairly standard B-class supergiant shining 83,000 times brighter than the Sun. It is thought to be a variable star and also a possible spectroscopic binary.
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