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 48.14991s[1]
Declination −48° 19′ 03.4699″[1]
Apparent magnitude (V) 5.7821 ± 0.0006[2]
Characteristics
Evolutionary stage Main sequence
Spectral type G4V[3]
U−B color index 0.05[4]
B−V color index 0.639 ± 0.003[2]
Astrometry
Radial velocity (Rv)−68.78±0.12[1] km/s
Proper motion (μ) RA: −1623.275±0.061 mas/yr[1]
Dec.: −275.548±0.072 mas/yr[1]
Parallax (π)67.8467 ± 0.0601 mas[1]
Distance48.07 ± 0.04 ly
(14.74 ± 0.01 pc)
Absolute magnitude (MV)4.80[5]
Details
Mass0.876+0.026
−0.032[3] M☉
Radius1.054±0.014[3] R☉
Luminosity1.038 ± 0.059[6] L☉
Surface gravity (log g)4.39 ± 0.11[6] cgs
Temperature5664 ± 61[6] K
Metallicity [Fe/H]−0.34±0.04[3] dex
Rotation23.8 ± 3.1 days [6]
Rotational velocity (v sin i)2.0 ± 0.5[7] km/s
Age11.7+2.1
−2.3[3] Gyr
Other designations
ν2 Lup, CD−47° 9919, GJ 582, HD 136352, HIP 75181, HR 5699, SAO 225697, TOI-2011, TIC 136916387[3]
Database references
SIMBADdata

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 of 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. As of 2023, the best parallax is 67.8467±0.0601 milli-arcseconds from Gaia DR3, corresponding to a distance of 48.07±0.04 light-years.[1]

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.[8] 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.[6][9][10][11]

Planetary system

The Nu2 Lupi planetary system[12][3]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b 4.68±0.40 M🜨 0.0963±0.0021 11.577794+0.000023
−0.000025 		0.079+0.068
−0.053 		88.53±0.11° 1.643±0.035 R🜨
c 11.22+0.60
−0.58 M🜨 		0.1717±0.0037 27.592076+0.000047
−0.000049 		0.037+0.039
−0.026 		88.580+0.032
−0.033° 		2.857+0.058
−0.057 R🜨
d 8.66+0.90
−0.91 M🜨 		0.4243±0.0092 107.1363+0.0019
−0.0024 		~0 89.766+0.036
−0.033° 		2.507±0.042 R🜨

On September 12, 2011, three low-mass planets were announced in a preprint, using data from the HARPS spectrograph.[13] These three planets are among about seven dozen planets discovered in September 2011, the most of any month up to that point during the exoplanet era that began in the early 1990s. The confirmation of these planets was published in Astronomy & Astrophysics in 2019.[14] The two inner planets were also detected using the transit method in 2020, allowing a precise determination of their masses and radii.[12] In 2021, planet d was also found to transit using observations from CHEOPS, allowing its mass and radius to be determined.[6] Further transit observations with CHEOPS were used to refine the planetary parameters and to search for signs of an exomoon around planet d, although no evidence of a moon was found.[3]

With a mass of about 5 Earth masses, the innermost planet falls into the regime of super-Earths, and was confirmed to be mostly rocky with a density of 7.8 g/cm3 in 2020.[12] The outer two planets straddle the boundary between super-Earths and Neptune-mass planets, so they are less likely to have predominantly rocky compositions. The middle planet Nu2 Lupi c with a density of 3.5 g/cm3 is expected to have a large gaseous envelope.[12] 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.[15]

See also

References

  1. ^ a b c d e f Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. ^ a b 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. S2CID 18759600. Vizier catalog entry
  3. ^ a b c d e f g h Ehrenreich, D.; Delrez, L.; et al. (February 2023). "A full transit of ν2 Lupi d and the search for an exomoon in its Hill sphere with CHEOPS". Astronomy & Astrophysics. 671: A154. arXiv:2302.01853. Bibcode:2023A&A...671A.154E. doi:10.1051/0004-6361/202244790. S2CID 256598325.
  4. ^ 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.
  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. ^ a b c d e f Delrez, Laetitia; Ehrenreich, David; et al. (2021). "Transit detection of the long-period volatile-rich super-Earth ν2 Lupi d with CHEOPS". Nature Astronomy. 5 (8): 775–787. arXiv:2106.14491. Bibcode:2021NatAs...5..775D. doi:10.1038/s41550-021-01381-5. ISSN 2397-3366. S2CID 235658761.
  7. ^ 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 (1): 141–166. Bibcode:2005ApJS..159..141V. doi:10.1086/430500.
  8. ^ Ecuvillon, A.; et al. (2007). "Kinematics of planet-host stars and their relation to dynamical streams in the solar neighbourhood". Astronomy and Astrophysics. 461 (1): 171–182. arXiv:astro-ph/0608669. Bibcode:2007A&A...461..171E. doi:10.1051/0004-6361:20065872. S2CID 16935788.
  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 (2): 297–318. arXiv:astro-ph/0607235. Bibcode:2007ApJS..168..297T. doi:10.1086/509763. S2CID 18775378.
  10. ^ 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. S2CID 18173201.
  11. ^ 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 [astro-ph.SR].
  12. ^ a b c d Kane, Stephen R.; et al. (2020), "Transits of Known Planets Orbiting a Naked-eye Star", The Astronomical Journal, 160 (3): 129, arXiv:2007.10995, Bibcode:2020AJ....160..129K, doi:10.3847/1538-3881/aba835, S2CID 220686518
  13. ^ 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 [astro-ph.EP].
  14. ^ Udry, S.; Dumusque, X.; et al. (February 2019). "The HARPS search for southern extra-solar planets. XLIV. Eight HARPS multi-planet systems hosting 20 super-Earth and Neptune-mass companions". Astronomy & Astrophysics. 622: A37. arXiv:1705.05153. Bibcode:2019A&A...622A..37U. doi:10.1051/0004-6361/201731173. S2CID 119095511.
  15. ^ 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 (2): 1206–1223. arXiv:1206.2370. Bibcode:2012MNRAS.424.1206W. doi:10.1111/j.1365-2966.2012.21298.x. S2CID 54056835. citing Beichman et al. 2006

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