Nu Indi

For the star previously named Nu Indi, see Nu Microscopii.

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.

Nu Indi

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]