Zeta Arae
Star in the constellation Ara
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Zeta Arae is the third-brightest star in the southern constellation Ara.[10] Its name is a Bayer designation that is Latinized from ζ Arae, and abbreviated Zeta Ara or ζ Ara. The apparent visual magnitude of this star is 3.1,[2] which can be seen with the naked eye from suburban skies in the southern hemisphere. From the parallax measurements, it is located at a distance of approximately 490 light-years (150 parsecs) from Earth.[1] The star is drifting closer to the Sun with a radial velocity of 6 km/s.[5]
 | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Ara |
| Right ascension | 16h 58m 37.213s[1] |
| Declination | −55° 59′ 24.50″[1] |
| Apparent magnitude (V) | 3.13[2] |
| Characteristics | |
| Evolutionary stage | AGB[3] |
| Spectral type | K3 III[4] |
| U−B color index | +1.96[2] |
| B−V color index | +1.60[2] |
| Astrometry | |
| Radial velocity (Rv) | −6.0±0.6[5] km/s |
| Proper motion (μ) | RA: −17.518 mas/yr[1] Dec.: −36.120 mas/yr[1] |
| Parallax (π) | 5.7725±0.1727 mas[1] |
| Distance | 570 ± 20 ly (173 ± 5 pc) |
| Absolute magnitude (MV) | −3.95[6] |
| Details | |
| Mass | 7–8[7] M☉ |
| Radius | 114±4[7] R☉ |
| Luminosity | 3,800+464 −414[7] L☉ |
| Surface gravity (log g) | 1.200±0.004[7] cgs |
| Temperature | 4,246+99 −96[7] K |
| Metallicity [Fe/H] | −0.40[8] dex |
| Other designations | |
| Tseen Yin, ζ Arae, CPD−55°7766, FK5 631, GC 22845, GJ 9581, HD 152786, HIP 83081, HR 6285, SAO 244315, PPM 345563[9] | |
| Database references | |
| SIMBAD | data |
| ARICNS | data |
The spectrum of this star matches a stellar classification of K3 III.[4] The luminosity class of 'III' indicates this is a giant star that has exhausted the hydrogen at its core and evolved away from the main sequence. However, some studies have suggested it is instead a supergiant.[6][11] The star has 7-8 times the mass of the Sun and has expanded to 114 times the Sun's girth. It is radiating 3,800[7] times the luminosity of the Sun from its photosphere at an effective temperature of 4,246 K,[7] giving it the orange hue of a K-type star.[12]
In 1997, an excess of infrared emission was announced that may indicate circumstellar matter.[13] However, a 2015 study found no excess.[14] A candidate gravitationally bound companion was announced in 2022. This object lies at an angular separation of 138.4″ from Zeta Arae, which is equivalent to a projected separation of 20.63×103 au.[15]
Nomenclature
In Chinese, 龜 (Guī), meaning Tortoise, refers to an asterism consisting of ζ Arae, ε1 Arae, γ Arae, δ Arae and η Arae.[16] Consequently, the Chinese name for ζ Arae itself is 龜五 (Guī wǔ, English: the Fifth Star of Tortoise.)[17]
R. H. Allen called it Tseen Yin /ˌsiːnˈjɪn/, together with δ Arae, from the Chinese 天陰 (Mandarin pronunciation tiānyīn) "dark sky".[18] However, 天陰 is in Aries.[19][20] so Allen probably confused constellation "Ara" with "Ari".