Nu Indi
Subgiant star in the constellation Indus
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Nu Indi is a star in the southern constellation of Indus. With an apparent visual magnitude of +5.278, it is faintly visible to the naked eye in sufficiently dark skies. Based upon parallax measurements, the star is 92.8 light-years distant.
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Indus[1] |
| Right ascension | 22h 24m 36.88539s[2] |
| Declination | −72° 15′ 19.4882″[2] |
| Apparent magnitude (V) | 5.278±0.005[3] |
| Characteristics | |
| Evolutionary stage | Subgiant[4][5][6][7][8] |
| Spectral type | G9V Fe-3.1CH-1.5[9] |
| Astrometry | |
| Radial velocity (Rv) | +32.51±0.16[10] km/s |
| Proper motion (μ) | RA: +1,303.872 mas/yr[2] Dec.: −674.186 mas/yr[2] |
| Parallax (π) | 35.1281±0.0640 mas[2] |
| Distance | 92.8 ± 0.2 ly (28.47 ± 0.05 pc)[2] |
| Absolute magnitude (MV) | +2.70±0.05[6] |
| Details | |
| Mass | 0.85±0.04[4] M☉ |
| Radius | 2.95±0.12[6] R☉ |
| Luminosity | 6.28±0.23[5] L☉ |
| Surface gravity (log g) | 3.43±0.10[6] cgs |
| Temperature | 5,318±80[6] K |
| Metallicity [Fe/H] | −1.54±0.07[6] dex |
| Rotational velocity (v sin i) | 2.67[11] km/s |
| Age | 11.0±0.7[4] Gyr |
| Other designations | |
| ν Indi, CD−72°1742, GJ 855.1, HD 211998, HIP 110618, HR 8515 | |
| Database references | |
| SIMBAD | data |
Characteristics
The spectrum of this star matches a classification of G9V Fe-3.1CH-1.5,[9] with the notation G9V suggesting it is a late-type G-type main sequence star. However, it is actually a subgiant,[4][5][6][7][8] a star which is running out of hydrogen in its core and expanding in size. The "Fe-3.1CH-1.5" indicate an underabundance of methylidyne radical and iron. The star has an overabundance of alpha elements, that is, elements heavier than carbon produced by nuclear reactions involving helium.[4] The metallicity indicators classify it as a Population II star.[6]
Nu Indi has been a target of asteroseismic studies since it displays solar-like oscillations.[7][8][4] It was the first metal-poor star of which asteroseismology has been applied.[8] Using this method, its mass and age have been measured at 0.85 solar masses and 11 billion years.[4] As a subgiant, it has expanded in size and become brighter, with a current radius of three solar radii[6] and a luminosity 6.3 times that of the Sun.[5] The effective temperature is 5,318 K,[6] giving it the yellow hue typical of G-type stars.[12]
It is a native member of the galactic halo which is currently crossing the galactic disk. The orbital eccentricity is somewhat high, at 0.60. It reaches a minimum distance of 8,000 light-years from the Galactic Center, and its distance relative to the galactic plane is no more than 4,900 ly.[4] It does not make part of any stellar association or moving group.[13]
Nu Indi was once thought to be a binary star whose components have spectral types of A3V and F9V, but this claim has since been disproven.[14] However, there is evidence it may be an astrometric binary.[6]