Kappa Aquarii

Kappa Aquarii is a candidate binary star in the equatorial constellation of Aquarius. Its identifier is a Bayer designation that is Latinized from κ Aquarii, and abbreviated Kappa Aqr or κ Aqr, respectively. This system is visible to the naked eye, but it is faint at an apparent visual magnitude of 5.03.^[3] Based upon parallax measurements, it is around 214 light-years (66 parsecs) from the Sun.^[5] The system is drifting further away from the Sun with a radial velocity of +7.3 km/s.^[6]

κ Aquarii

Location of κ Aquarii (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Aquarius[1]
Right ascension	22h 37m 45.381s[2]
Declination	−04° 13′ 41.00″[2]
Apparent magnitude (V)	5.030±0.009[3]
Characteristics
Spectral type	K1.5 IIIb CN0.5[4]
U−B color index	+1.16[5]
B−V color index	+1.142[6]
Astrometry
Radial velocity (Rv)	+7.31±0.16[6] km/s
Proper motion (μ)	RA: −69.411 mas/yr[2] Dec.: −119.631 mas/yr[2]
Parallax (π)	14.7149±0.0995 mas[2]
Distance	222 ± 1 ly (68.0 ± 0.5 pc)
Absolute magnitude (MV)	+0.96[1]
Details
Mass	2.554±0.128[7] M☉
Radius	13[6] R☉
Luminosity	60[6] L☉
Surface gravity (log g)	2.63±0.08[3] cgs
Temperature	4,581±5[6] K
Metallicity [Fe/H]	+0.14±0.04[3] dex
Rotational velocity (v sin i)	3.8[6] km/s
Other designations
Situla, 63 Aquarii, BD−04 5716, FK5 1595, GC 31581, HD 214376, HIP 111710, HR 8610, SAO 146210, PPM 206585, WDS J22378-0414A[8]
Database references
SIMBAD	data

The two components are designated Kappa Aquarii A and B. The former is named Situla, pronouced /ˈsɪtjuːlə/, the traditional name for the system.^[9]

Nomenclature

κ Aquarii (Latinised to Kappa Aquarii) is the system's Bayer designation. The designations of the two components as Kappa Aquarii A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).^[10]

It bore the traditional name Situla, a Latin word meaning "bucket" or "water jar".^[11] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)^[12] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.^[13] It approved the name Situla for the component Kappa Aquarii A on 12 September 2016 and it is now so included in the List of IAU-approved Star Names.^[9]

In Chinese, 虛梁 (Xū Liáng), meaning Temple, refers to an asterism consisting of Kappa Aquarii, 44 Aquarii, 51 Aquarii and HD 216718.^[14] Consequently, the Chinese name for Kappa Aquarii itself is 虛梁三 (Xū Liáng sān, English: the Third Star of Temple).^[15] From this Chinese name, the name Heu Leang has appeared, meaning "the empty bridge".^[11]

Properties

Kappa Aquarii is most probably a wide binary star system.^[16] The brighter component is a giant star with a stellar classification of K1.5 IIIb CN0.5.^[4] It has exhausted the supply of hydrogen at its core and has expanded to 13^[6] times the radius of the Sun. It is radiating 60^[6] times the Sun's luminosity from its photosphere at an effective temperature of 4,581 K,^[6] giving it the orange-hued glow of a K-type star.^[17]

The fainter companion star is located at an angular separation of 98.3 arcseconds and has an apparent magnitude of 8.8.^[17]

In culture

Endymion, an 1818 poem by John Keats, describes the star in its form as a water urn thus:

Crystalline brother of the belt of heaven,
Aquarius! to whom King Jove has given
Two liquid pulse streams 'stead of feather'd wings,
Two fan-like fountains, — thine illuminings.^[18]

USS Situla (AK-140) was a United States Navy Crater-class cargo ship named after the star.