Theta Librae
Star in the constellation Libra
From Wikipedia, the free encyclopedia
Theta Librae is a single[9] star in the southern zodiac constellation of Libra, near the constellation border with Scorpius. Its name is a Bayer designation that is Latinized from θ Librae, and abbreviated Theta Lib or θ Lib. It is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.14.[2] The distance to this star is approximately 168 light years, as determined by parallax, and it is drifting further away with a radial velocity of 5 km/s.[5] The position of this star near the ecliptic means it is subject to lunar occultations.[10]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Libra |
| Right ascension | 15h 53m 49.53806s[1] |
| Declination | −16° 43′ 45.4582″[1] |
| Apparent magnitude (V) | 4.136[2] |
| Characteristics | |
| Evolutionary stage | red clump[2] |
| Spectral type | G9IIIb[3] |
| U−B color index | +0.82[4] |
| B−V color index | +1.01[4] |
| Astrometry | |
| Radial velocity (Rv) | 4.56±0.25[5] km/s |
| Proper motion (μ) | RA: +100.33[1] mas/yr Dec.: +135.02[1] mas/yr |
| Parallax (π) | 19.36±0.15 mas[6] |
| Distance | 168 ± 1 ly (51.7 ± 0.4 pc) |
| Absolute magnitude (MV) | 0.665[2] |
| Details | |
| Mass | 1.47[7] M☉ |
| Radius | 12.27[7] R☉ |
| Luminosity | 68.1[7] L☉ |
| Surface gravity (log g) | 2.44[7] cgs |
| Temperature | 4,739[7] K |
| Metallicity [Fe/H] | −0.35[7] dex |
| Rotational velocity (v sin i) | 0.0[5] km/s |
| Age | 3.4[7] Gyr |
| Other designations | |
| θ Lib, 46 Librae, BD−16°4174, HD 142198, HIP 77853, HR 5908, SAO 159563[8] | |
| Database references | |
| SIMBAD | data |
This object is an aging giant star with a stellar classification of G9IIIb.[3] Having exhausted the supply of hydrogen at its core, it has cooled and expanded; at present it has 12.3 times the girth of the Sun.[7] The star has an estimated mass about 47% greater than the Sun. It is radiating about 68 times the luminosity of the Sun from its photosphere at an effective temperature of about 4,739 K.[7] It is probably on the red giant branch, which indicates it is generating energy through hydrogen fusion in a shell outside an inert helium core.[7] However, there is a 41% chance that it is a red clump giant on the horizontal branch,[2] which would mean it was somewhat older and less massive.[7] It has sometimes been classified spectroscopically as a subgiant, but detailed study shows that it is too cool and luminous to be on the subgiant branch.[11]