Nu² Lupi

ν² Lupi

A star chart of the constellation of Lupus showing the position of ν2
Observation data Epoch J2000      Equinox J2000
Constellation	Lupus
Right ascension	15h 21m 48.15s ± 3.25[1]
Declination	−48° 19′ 03.46″ ± 3.16[1]
Apparent magnitude (V)	5.7821 ± 0.0006[1]
Characteristics
Evolutionary stage	Main sequence
Spectral type	G4V[2]
U−B color index	0.05[3]
B−V color index	0.639 ± 0.003[1]
Astrometry
Radial velocity (Rv)	68.7120 ± 0.0005[4] km/s
Proper motion (μ)	RA: -1622.61 ± 0.37[1] mas/yr Dec.: -275.62 ± 0.36[1] mas/yr
Parallax (π)	68.159 ± 0.098[5] mas
Distance	47.85 ± 0.07 ly (14.67 ± 0.02 pc)
Absolute magnitude (MV)	4.80[6]
Details
Mass	0.87 ± 0.04[7] M☉
Radius	1.058 ± 0.019[7] R☉
Luminosity	1.038 ± 0.059[7] L☉
Surface gravity (log g)	4.39 ± 0.11[7] cgs
Temperature	5664 ± 61[7] K
Metallicity [Fe/H]	-0.24 ± 0.05[7] dex
Rotation	23.8 ± 3.1 days [7]
Rotational velocity (v sin i)	2.0 ± 0.5[8] km/s
Age	12.3+1.2 −2.9[7] Gyr
Other designations
ν2 Lup, CD−47° 9919, Gaia DR2 5902750168276592256, GJ 582, HD 136352, HIP 75181, HR 5699, SAO 225697
Database references
SIMBAD	data
Extrasolar Planets Encyclopaedia	data

Nu² Lupi (ν² Lupi) is a 6th magnitude G-type main-sequence star located approximately 48 light-years away in the constellation of Lupus. The physical properties of the star are similar to those of the Sun, though Nu² Lupi is significantly older.

Properties[]

Nu² Lupi is a bright star, barely observable with the naked eye in good observing conditions, that lies towards the bottom Lupus near to the border with Norma and close to the galactic plane.

At over 1.6 arcseconds per year, Nu² Lupi has a particularly large proper motion. This indicates that the star is nearby, which was confirmed by Earth-based parallax measurements during the last century such as that of the Gliese Catalogue of Nearby Stars, measuring 63.1 ± 7.8 milli-arcseconds. The much more accurate space-based Hipparcos parallax of 67.51 ± 0.39 milli-arcseconds gives a distance of 48.3 ± 0.3 light-years, making Nu² Lupi one of the closest G-type main-sequence stars to the Sun.

Somewhat surprisingly, Nu² Lupi also has a large radial velocity of -68.7 km/s. When combined with its large proper motion, it becomes apparent that the star is moving much faster through the galaxy than the Sun. This indicates that the star is a member of an older, higher-motion stellar population, which is confirmed by the star's position on the Toomre diagram with Nu² Lupi showing kinematics of a thick disk star.^[9] This means that Nu² Lupi must be considerably older than the Sun, which is supported by its spectroscopic parameters: the depth of the star's iron spectral lines implies an iron abundance of -0.34 ± 0.01 dex, equalling 46 ± 1% of the solar iron abundance - a typical value for a thick disk star. Similarly, the star's surface gravity of log 4.39 ± 0.11 g is somewhat lower than is typical for a main-sequence G-type star and indicates modest evolution, which when combined with a spectroscopically derived mass of 0.87 ± 0.03 M_☉ implies an age of around 12.3 billion years, over twice the solar age. Nu² Lupi is therefore probably one of the oldest stars in the solar neighbourhood.^{[7][10][11][12]}

Planetary system[]