Nu2 Lupi

Nu2 Lupi (ν2 Lup) 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.

For other star systems with this Bayer designation, see ν 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
Spectral type G2V
U−B color index 0.05[2]
B−V color index 0.639 ± 0.003[1]
Astrometry
Radial velocity (Rv)68.7120 ± 0.0005[3] 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[4] mas
Distance47.85 ± 0.07 ly
(14.67 ± 0.02 pc)
Absolute magnitude (MV)4.80[5]
Details
Mass0.906+0.055
−0.047[4] M☉
Radius1.012±0.018[4] R☉
Luminosity1.081+0.088
−0.082[4] L☉
Surface gravity (log g)4.385+0.029
−0.027[4] cgs
Temperature5664 ± 14[6] K
Metallicity [Fe/H]-0.34 ± 0.01[6] dex
Rotation25.0 ± 3.1 days[7]
Rotational velocity (v sin i)2.0 ± 0.5[8] km/s
Age10.36 ± 2.30[9] Gyr
Other designations
CD−47° 9919, Gaia DR2 5902750168276592256, GJ 582, HD 136352, HIP 75181, HR 5699, SAO 225697
Database references
SIMBADdata
Extrasolar Planets
Encyclopaedia		data

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.[10] 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 ± 0.02 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 0.91 ± 0.03 M☉ implies an age of 10.36 ± 2.30 billion years, over twice the solar age. Nu2 Lupi is therefore probably one of the oldest stars in the solar neighbourhood.

Planetary system

On September 12, 2011 three low-mass planets were announced using data from the HARPS spectrograph.[3] These three planets are among about seven dozen planets discovered in September 2011, the most of any month during the exoplanet era that begun in early 1990s. The two inner planet were also found using a transit method in 2020, allowing a precise determination of their mass and radii.[4]

With a minimum mass of about 5 Earth masses, the innermost planet falls into the regime of Super-Earths, and was confirmed to be mostly rocky with density 7.8 g/cm3 in 2020.[4] Outer planets straddle the commonly accepted upper limit between Super-Earths and Neptunes at 10 M⊕, so it could be either predominantly rocky or gaseous. The middle planet Nu2 Lupi c with density 3.5 g/cm3 is expected to have a large gaseous envelope.[4] All three planets orbit within 0.5 AU and are likely too hot to maintain liquid water.

The most recent published observation of this system for debris disks was in 2006 by the Spitzer telescope, searching for an excess of infra-red light that would indicate scattering of starlight by dust or planetesimals; no infra-red excess was detected.[11]

The Nu2 Lupi planetary system[4]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b 4.62+0.45
−0.44 M⊕		 0.0969+0.0019
−0.0017		 11.57779+0.00091
−0.0011		 0.079+0.068
−0.053		 88.86+0.54
−0.30°		 1.482+0.058
−0.056 R⊕
c 11.29+0.73
−0.69 M⊕		 0.1729+0.0034
−0.0030		 27.5909+0.0028
−0.0031		 0.037+0.039
−0.026		 88.658+0.055
−0.057°		 2.608+0.078
−0.077 R⊕
d ≥9.59 ± 1.86 M⊕ 0.4285+0.0085
−0.0076		 107.63+0.18
−0.19		 0.075+0.085
−0.053		 — —

See also

References
  1. van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. Vizier catalog entry
  2. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D.
  3. Mayor, M.; et al. (2011). "The HARPS search for southern extra-solar planets XXXIV. Occurrence, mass distribution and orbital properties of super-Earths and Neptune-mass planets". arXiv:1109.2497. Bibcode:2011arXiv1109.2497M. Cite journal requires |journal= (help)
  4. Transits of Known Planets Orbiting a Naked-Eye Star, 2020, arXiv:2007.10995
  5. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  6. Sousa, S. G.; et al. (August 2008). "Spectroscopic parameters for 451 stars in the HARPS GTO planet search program. Stellar [Fe/H] and the frequency of exo-Neptunes". Astronomy and Astrophysics. 487 (1): 373–381. arXiv:0805.4826. Bibcode:2008A&A...487..373S. doi:10.1051/0004-6361:200809698.
  7. Lovis, C.; et al. (2011). "The HARPS search for southern extra-solar planets. XXXI. Magnetic activity cycles in solar-type stars: statistics and impact on precise radial velocities". arXiv:1107.5325. Bibcode:2011arXiv1107.5325L. Cite journal requires |journal= (help)
  8. Valenti, J. A.; Fischer, D. A. (2005). "Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs". The Astrophysical Journal Supplement Series. 159: 141–166. Bibcode:2005ApJS..159..141V. doi:10.1086/430500.
  9. Takeda, Genya; et al. (2007). "Structure and Evolution of Nearby Stars with Planets. II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog". The Astrophysical Journal Supplement Series. 168: 297–318. arXiv:astro-ph/0607235. Bibcode:2007ApJS..168..297T. doi:10.1086/509763.
  10. Ecuvillon, A.; et al. (2007). "Kinematics of planet-host stars and their relation to dynamical streams in the solar neighbourhood". Astronomy and Astrophysics. 461: 171–182. arXiv:astro-ph/0608669. Bibcode:2007A&A...461..171E. doi:10.1051/0004-6361:20065872.
  11. Wyatt, M. C.; et al. (2012). "Herschel imaging of 61 Vir: implications for the prevalence of debris in low-mass planetary systems". Monthly Notices of the Royal Astronomical Society. 424: 1206–1223. arXiv:1206.2370. Bibcode:2012MNRAS.424.1206W. doi:10.1111/j.1365-2966.2012.21298.x. citing Beichman et al. 2006

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