Phi Cassiopeiae is a multiple star system in the northern constellation of Cassiopeia. Its name is a Bayer designation that is Latinized from ÃÂ Cassiopeiae, and abbreviated Psi Cas or ÃÂ Cas. With a combined apparent magnitude of +4.95, it is visible to the naked eye. The two brightest components are A and C, sometimes called ÃÂ<sup>1</sup> and ÃÂ<sup>2</sup> Cas. ÃÂ Cas A is an F0 bright supergiant of magnitude 4.95 and ÃÂ Cas C is a 7.08 magnitude B6 supergiant at 134".
ÃÂ Cassiopeiae appears among the stars of the open cluster NGC 457, which located at a distance of , but it is uncertain whether ÃÂ Cas is a member of this cluster. ÃÂ Cas is generally treated as having five component stars, designated A to E in order of distance from the brightest star. The two components A and C are the brightest stars in the field of NGC 457; they are sometimes referred to as ÃÂ<sup>1</sup> and ÃÂ<sup>2</sup> Cassiopeiae. Component B is a 12th magnitude star 49" from ÃÂ<sup>1</sup>.
Components D and E and both 10th magnitude B-type main sequence stars in the field of NGC 457, with component E only 42" from ÃÂ<sup>2</sup>. Another three components are sometimes listed as components of the multiple system, although this is somewhat arbitrary with dozens of members of NGC 457 being found within a few arc-minutes.
The two supergiants, components A and C, share a similar space motion to the other stars in NGC 457, but their evolutionary status and brightness makes them unlikely members. Their Gaia Data Release 2 parallaxes are comparable to other stars in the cluster and consistent with the accepted distance of NGC 457, and component C has been given a 70% likelihood of being a member of the cluster.
The primary component of the ÃÂ Cassiopeiae system is a very luminous yellow supergiant. Its absolute magnitude is comparable to some yellow hypergiants but it does not show the level of mass loss and instability that would qualify it as a hypergiant itself. Various model atmospheres all give a temperature around 7,300K, a low surface gravity, a radius around , and a luminosity well over . More uncertain is the mass, which would be expected to have been well over initially, but much less now. Different authors have published values from to .
Component C is a relatively typical B class supergiant, 83,000 times the luminosity of the sun. It is a suspected variable and a suspected spectroscopic binary.