18 Scorpii

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Template:Short description

18 Scorpii
Template:Location mark
Location of 18 Scorpii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Scorpius[1]
Right ascension Template:RA[2]
Declination Template:DEC[2]
Apparent magnitude (V) 5.503[3]
Characteristics
Evolutionary stage main sequence[4]
Spectral type G2 Va[5]
U−B Template:Engvar +0.18[6]
B−V Template:Engvar +0.64[6]
Variable type Sun-like[7]
Astrometry
Radial velocity (Rv)Template:Val[2] km/s
Proper motion (μ) RA: +232.230 mas/yr[2]
Dec.: −495.378 mas/yr[2]
Parallax (π)70.7371±0.0631 mas[2]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)4.77[3]
Details[8]
MassTemplate:Val Template:Solar mass
RadiusTemplate:Val Template:Solar radius
LuminosityTemplate:Val Template:Solar luminosity
Surface gravity (log g)Template:Val cgs
TemperatureTemplate:Val[9] K
Metallicity [Fe/H]Template:Val dex
RotationTemplate:Val[10]
AgeTemplate:Val[11] Gyr
5.64 or 7.18[9] Gyr
Metallicity [Fe/H]{{{metal_fe2}}} dex
Other designations
Template:Odlist[12]
Database references
SIMBADdata
Exoplanet Archivedata

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18 Scorpii is a solitary star located at a distance of some Template:Convert from the Sun at the northern edge of the Scorpius constellation. It has an apparent visual magnitude of 5.5,[3] which is bright enough to be seen with the naked eye outside of urban areas. The star is drifting further away with a radial velocity of +11.6.[3]

18 Scorpii has some physical properties in common with the Sun, a G-type star. Cayrel de Strobel (1996) included it in her review of the stars most similar to the Sun,[13] and Porto de Mello & da Silva (1997) identified it as a younger solar twin.[14][15] Some scientists therefore believe the prospects for life in its vicinity are good.

Characteristics

File:18 scorpii-map.png
18 scorpii is on the northern boundary of the constellation. Its high proper motion positions it in Ophiuchus before 1700.
File:The life cycle of a Sun-like star (annotated).jpg
The age of 18 Scorpii, shown relative to the Sun, the older solar twin HD 197027, here annotated as HIP 102152 and the formation of the Milky Way

18 Scorpii is a main sequence star of spectral and luminosity type G2 Va,[15] with the luminosity class of 'V' indicating it is generating energy through the nuclear fusion of hydrogen in its core region. Sousa et al. (2008) found its metallicity to be about 1.1 times that of the Sun, which means the abundance of elements other than hydrogen or helium is 10% greater.[16][17] The radius of this star, as measured using interferometry by Bazot et al. (2011), is 101% the radius of the Sun. When combined with the results of asteroseismology measurements, this allows the mass of the star to be estimated as 102% of the Sun's mass.[18] This star is radiating 106% of the Sun's luminosity from its outer atmosphere at an effective temperature of 5,433 K.[19] It is this heat that gives the star the yellow-hued glow of a G-type star.[20]

According to Lockwood (2002), it has a temporal photometric behavior very similar to the Sun.[21] Its brightness variation over its entire activity cycle is 0.09%, about the same as the Sun's brightness variations during recent solar cycles.[22] Using the technique of Zeeman-Doppler imaging, Petit et al. (2008) have detected its surface magnetic field, showing that its intensity and geometry are very similar to the large-scale solar magnetic field.[23] The estimated period for the activity cycle of 18 Scorpii is about seven years,[7] which is significantly shorter than the Sun's, and its overall chromospheric activity level is noticeably higher.[22][24] Like the Sun, it has a hot corona with a temperature in the range of 1.5–2 MK and an X-ray luminosity of 8 ± 1.5 ergs s−1.[10]

Though 18 Scorpii is only slightly more metal-rich overall than the Sun, its lithium abundance is about three times as high; for this reason, Meléndez & Ramírez (2007) have suggested that 18 Scorpii be called a "quasi solar twin", reserving the term solar twin for stars (such as HIP 56948) that match the Sun, within the observational errors, for all parameters.[25]

Template:Clearleft

Search for planets

18 Scorpii was identified in September 2003 by astrobiologist Margaret Turnbull from the University of Arizona in Tucson as one of the most promising nearby candidates for hosting life, based on her analysis of the HabCat list of stars. This is a solitary star,[26] and does not display the level of excess infrared emission that would otherwise suggest the presence of unconsolidated circumstellar matter, such as a debris disk.[27]

In a paper published in April 2017, a candidate planet was found orbiting 18 Scorpii (HD 146233) with a period of Template:Convert,[28] but subsequent studies in 2020 and 2023 found that the radial velocity signal originates from a stellar activity cycle.[29][30]Template:Rp However, in 2023 evidence of a different candidate planet was found, which would be of super-Earth mass with a period of 19.9 days.[30]Template:Rp The same planet was detected in 2025.[31]

Template:OrbitboxPlanet begin Template:OrbitboxPlanet hypothetical Template:Orbitbox end

References

Template:Reflist

External links

Template:Stars of Scorpius

  1. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named xhip
  2. ↑ a b c d e Cite error: Invalid <ref> tag; no text was provided for refs named GaiaDR3
  3. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named aaa418_989
  4. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named petit2008
  5. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Keenan1989
  6. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named eggen1986
  7. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named aj138_1_312
  8. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Karovicova
  9. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named Bazot2018
  10. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named baas42_333
  11. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named nasa
  12. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named SIMBAD
  13. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named aar7_3_243
  14. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named eso
  15. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named apj482_2_L89
  16. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named aaa487_1_373
  17. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named metal
  18. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named aaa526_L4
  19. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj746_1_101
  20. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named csiro
  21. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named baas34_651
  22. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named aj133_5_2206
  23. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named mnras388_1_80
  24. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj545_2_L43
  25. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj669_2_L89
  26. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named mea2005
  27. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj705_1_89
  28. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Butler2017
  29. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Hirsch2020
  30. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named Laliotis2023
  31. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named gupta2025
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