  | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cassiopeia[1] |
| Right ascension | 00h 56m 39.90413s[2] |
| Declination | +59° 10′ 51.8006″[2] |
| Apparent magnitude (V) | +4.62[3] |
| Characteristics | |
| Evolutionary stage | horizontal branch[4] |
| Spectral type | G8 IIIb Fe−0.5[5] |
| U−B color index | +0.68[3] |
| B−V color index | +0.96[3] |
| Astrometry | |
| Radial velocity (Rv) | −47.73±0.12[6] km/s |
| Proper motion (μ) | RA: −92.085[2] mas/yr Dec.: −45.079[2] mas/yr |
| Parallax (π) | 17.2875±0.1880 mas[2] |
| Distance | 189 ± 2 ly (57.8 ± 0.6 pc) |
| Absolute magnitude (MV) | +0.62[7] |
| Details[6] | |
| Mass | 1.44±0.16 M☉ |
| Radius | 10.44+0.24 −0.50[2] R☉ |
| Luminosity | 55.3±0.7[2] L☉ |
| Surface gravity (log g) | 2.75±0.19 cgs |
| Temperature | 4,937±14 K |
| Metallicity [Fe/H] | −0.35±0.03 dex |
| Rotational velocity (v sin i) | 0.54±0.38 km/s |
| Age | 2.20±0.62 Gyr |
| Other designations | |
| Castula, υ2 Cas, 28 Cassiopeiae, BD+58°138, HD 5395, HIP 4422, HR 265, SAO 21855 | |
| Database references | |
| SIMBAD | data |
Upsilon2 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.[8] The star has a yellow hue and is faintly visible to the naked eye with an apparent visual magnitude of +4.62.[3] Based upon parallax measurements, it is located at a distance of approximately 189 light years from the Sun.[2] The star is drifting closer with a radial velocity of −48 km/s.[6]
This is an aging giant star with a stellar classification of G8 IIIb Fe−0.5,[5] 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[2] times the girth of the Sun. It is a red clump giant, which means it is on the horizontal branch undergoing core helium fusion.[4]
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.[7] It is 2.2 billion years old with 1.44 times the mass of the Sun.[6] The star is radiating 55[2] times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,937 K.[6]
Upsilon2 Cassiopeiae, Latinised from υ2 Cassiopeiae, is the star's Bayer designation.
This star bore the name Castula in Bayer's Uranometria, which is Latin for a type of woman's tunic.[9] In 2016, the IAU organized a Working Group on Star Names (WGSN)[10] 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.[8]
