Alpha Indi
Star in the constellation Indus
From Wikipedia, the free encyclopedia
Alpha Indi (α Ind, α Indi) is the brightest star in the southern constellation Indus. Parallax measurements imply that it is located about 100 light years from Earth.[1] It has an apparent visual magnitude of 3.22,[2] being readily visible to the naked eye, and has an absolute magnitude of +0.78.[6]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Indus |
| Right ascension | 20h 37m 34.032s[1] |
| Declination | −47° 17′ 29.41″[1] |
| Apparent magnitude (V) | 3.11[2] |
| Characteristics | |
| Evolutionary stage | red clump[3] |
| Spectral type | K0 III–IV[4] |
| U−B color index | +0.79[2] |
| B−V color index | +1.00[2] |
| Astrometry | |
| Radial velocity (Rv) | −1.3[5] km/s |
| Proper motion (μ) | RA: +50.922 mas/yr[1] Dec.: +66.026 mas/yr[1] |
| Parallax (π) | 32.8989±0.2225 mas[1] |
| Distance | 99.1 ± 0.7 ly (30.4 ± 0.2 pc)[1] |
| Absolute magnitude (MV) | 0.78±0.03[6] |
| Details[6] | |
| Mass | 2.15±0.13 M☉ |
| Radius | 9.89±0.21 R☉ |
| Luminosity | 50.9±1.6 L☉ |
| Surface gravity (log g) | 2.73±0.094 cgs |
| Temperature | 4,904±37 K |
| Metallicity [Fe/H] | −0.038±0.029 dex |
| Age | 1.572±0.273[7] Gyr |
| Other designations | |
| HD 196171, HR 7869, SAO 230300, FK5 769, CD−47°13477, HIP 101772[8] | |
| Database references | |
| SIMBAD | data |
Characteristics
The stellar classification of Alpha Indi is K0 III-IV,[4] meaning that it has exhausted the hydrogen at its core and evolved away from the main sequence, being now halfway between a subgiant and a giant star. It is estimated to be 1.6 billion years old,[7] has 2.15 times the mass of the Sun, but has expanded to 9.9 times the radius of the Sun and irradiates 51 times its luminosity. The effective temperature of its photosphere is 4,900 K,[6] giving it the characteristic orange hue of a K-type star.[9] It may have two nearby M-type companion stars, which are located at least 2,000 AU from the primary.[10]
Nomenclature
Alpha Indi is the star's Bayer designation.[8] In China, this star is called Pe Sze where it also was known as the Persian, a title from the Jesuit missionaries.[11] The term Pe Sze is from the name of asterism 波斯 (Bō Sī, English: Persia). In Chinese astronomy, consequently, α Indi itself is known as 波斯二 (Bō Sī èr, English: the Second Star of Persia)[12]