  | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 19h 04m 40.98177s[1] |
| Declination | −21° 44′ 29.3845″[1] |
| Apparent magnitude (V) | +3.771[2] |
| Characteristics | |
| Evolutionary stage | horizontal branch[3] |
| Spectral type | G9IIIb[4] |
| B−Vcolor index | +1.012±0.008[5] |
| Astrometry | |
| Radial velocity (Rv) | +26.1±0.6[5] km/s |
| Proper motion (μ) | RA: +76.35±0.31[1]mas/yr Dec.: −58.12±0.18[1]mas/yr |
| Parallax (π) | 22.96±0.24 mas[1] |
| Distance | 142 ± 1 ly (43.6 ± 0.5 pc) |
| Absolute magnitude (MV) | 0.625[2] |
| Details | |
| Mass | 1.80[6] M☉ |
| Radius | 12.09+0.29 −0.17[7] R☉ |
| Luminosity | 66.7±1.1[7] L☉ |
| Surface gravity (log g) | 2.66[2] cgs |
| Temperature | 4,744+34 −57 K |
| Metallicity[Fe/H] | −0.04[2] dex |
| Age | 2.39[6] Gyr |
| Other designations | |
| ο Sgr,39 Sagittarii,BD−21°5237,GC 26224,HD 177241,HIP 93683,HR 7217,SAO 187643,PPM 269274,ADS 11996,CCDM J19047-2144A,WDS J19047-2144A[8] | |
| Database references | |
| SIMBAD | data |
ο Sagittarii, Latinized asOmicron Sagittarii, is a single[9] star in theconstellationSagittarius. It is yellow in hue and visible to the naked eye with anapparent visual magnitude of +3.77.[2] The distance to this star is approximately 142 light years based onparallax.[1] It is drifting further away from the Sun with aradial velocity of +26 km/s, having come to within 86 ly around a million years ago.[5]
This object is position 0.86 degrees north of theecliptic, so ο Sagittarii can beocculted by theMoon and very rarely byplanets. The last occultation by a planet took place on 24 December 1937, when it was occulted byMercury.[citation needed] It was almost eclipsed by the sun, which occupies a mean, rounded, half of one degree of the sky, on 5 January.[10] Thus the star can be viewed the whole night, crossing the sky, in early July.
This is an aginggiant star with astellar classification of G9IIIb.[4] It is classified as ared clump giant, suggesting it is on thehorizontal branch undergoingcorehelium fusion.[3] The star is 2.39 billion years old[6] with 1.80 times themass of the Sun.[6] It has expanded to 12 times theradius of the Sun and is radiating 67 times theSun's luminosity from its swollenphotosphere at aneffective temperature of 4,744 K.[7]
It has a faint, magnitude 13.8 companion, designated component B and positioned38.4″ away along aposition angle of 252°, as of 2010.[11]
InChinese,建 (Jiàn), meaningEstablishment, refers to an asterism consisting of ο Sagittariiξ² Sagittarii,π Sagittarii,43 Sagittarii,ρ¹ Sagittarii andυ Sagittarii. Consequently, theChinese name for ο Sagittarii itself is建二 (Jiàn èr, English:the Second Star of Establishment.)[12]
This star is occasionally called by the nameManubrium, usually in anastrological context.[13]
