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Upsilon2 Cassiopeiae
Upsilon2 Cassiopeiae, Latinised from υ2 Cassiopeiae, is a solitary star in the constellation of Cassiopeia, a few degrees to the south of Gamma Cassiopeiae. It has the proper name Castula /ˈkæstjʊlə/, which has been officially adopted by the IAU.[7] The star has a yellow hue and is faintly visible to the naked eye with an apparent visual magnitude of +4.62.[2] Based upon parallax measurements, it is located at a distance of approximately 189 light years from the Sun.[1] The star is drifting closer with a radial velocity of −48 km/s.[5] This is an aging giant star with a stellar classification of G8 IIIb Fe−0.5,[4] where the suffix notation indicates a mild underabundance of iron in the spectrum. With the supply of core hydrogen exhausted, this star has cooled and expanded off the main sequence – at present it has 10[1] times the girth of the Sun. It is a red clump giant, which means it is on the horizontal branch undergoing core helium fusion.[3] Upsilon2 Cassiopeiae is a barium star, showing an excess of the element barium in its spectrum. This can occur from mass transfer from a more-evolved companion star that later became a white dwarf, although no companion has been detected.[6] It is 2.2 billion years old with 1.44 times the mass of the Sun.[5] The star is radiating 55[1] times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,937 K.[5] Nomenclatureυ2 Cassiopeiae is the star's Bayer designation. In 2016, the IAU organized a Working Group on Star Names (WGSN)[8] to catalog and standardize proper names for stars. The WGSN approved the name Castula for this star on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[7] References
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