18 Scorpii

Star in the constellation Scorpius Ophiuchus constellation map.svg center 260 right Red circle.svg 8 18 Sco 820 558 Location of 18 Scorpii (circled) J2000.0 Scorpius 16 15 37.27028 -08 22 09.9821 5.503 main sequence G2 Va +0.64 +0.18 Sun-like 11.71 0.12 +232.230 −495.378 70.7371 0.0631 4.77 1.02 0.01 1.007 0.011 1.043 0.005 5808 3 commas 4.437 0.013 0.041 0.003 4.30 0.28 0.27 22.7 0.5 days -07°4242 616 146233 79672 6060 141066 21864 16156-0822 18+Sco 18 Sco 18 Scorpii is a solitary star located at a distance of some 14.13 pc ly flip off on from the Sun at the northern edge of the Scorpius constellation. It has an apparent visual magnitude of 5.5, which is bright enough to be seen with the naked eye outside of urban areas. The star is drifting farther away with a radial velocity of +11.6. 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, and Porto de Mello & da Silva (1997) identified it as a younger solar twin. Some scientists therefore believe the prospects for life in its vicinity are good. Characteristics left|240px|thumb|18 scorpii is on the northern boundary of the constellation. Its high proper motion positions it in Ophiuchus before 1700. thumb|left|300px|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, 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. 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. This star is radiating 106% of the Sun's luminosity from its outer atmosphere at an effective temperature of 5,433 K. It is this heat that gives the star the yellow-hued glow of a G-type star. According to Lockwood (2002), it has a temporal photometric behavior very similar to the Sun. Its brightness variation over its entire activity cycle is 0.09%, about the same as the Sun's brightness variations during recent solar cycles. 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. The estimated period for the activity cycle of 18 Scorpii is about seven years, which is significantly shorter than the Sun's, and its overall chromospheric activity level is noticeably higher. 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. 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. 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, 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. In a paper published in April 2017, a candidate planet was found orbiting 18 Scorpii (HD 146233) with a period of 2529 days years, but subsequent studies in 2020 and 2023 found that the radial velocity signal originates from a stellar activity cycle.38 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.38 The same planet was detected in 2025. 6.77 0.86 ≥ 19.8777 0.0062 0.38 0.16 References 4345775217221821312 Karovicova I. White T. R. Nordlander T. Casagrande L. Ireland M. Huber D. 13 September 2021 Fundamental stellar parameters of benchmark stars from CHARA interferometry -- II. 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The Night Time Sun: X-Ray Observations of the Solar Twin 18 Scorpii Bulletin of the American Astronomical Society 42 333 2010AAS...21542417C January 2010 Martos Giulia Meléndez Jorge Rathsam Anne Carvalho-Silva Gabriela 2023-04-21 Metallicity and age effects on lithium depletion in solar analogues Monthly Notices of the Royal Astronomical Society 522 3 3217–3226 10.1093/mnras/stad1177 2305.01861 free 2023MNRAS.522.3217M 0035-8711 1 Lawler S. M. Beichma C. A. Bryden G. Ciardi D. R. Tanner A. M. Su K. Y. L. Stapelfeldt K. R. Lisse C. M. Harker D. E. Explorations Beyond the Snow Line: Spitzer/IRS Spectra of Debris Disks Around Solar-type Stars The Astrophysical Journal 705 1 89–111 10.1088/0004-637X/705/1/89 2009ApJ...705...89L 0909.0058 2009 1272803 Butler R. Paul etal The LCES HIRES/Keck Precision Radial Velocity Exoplanet Survey The Astronomical Journal 13 April 2017 153 5 208 10.3847/1538-3881/aa66ca 2017AJ....153..208B 1702.03571 2299/18220 14954371 free Planet candidate is in Table 2; full table available here. Understanding the Impacts of Stellar Companions on Planet Formation and Evolution: A Survey of Stellar and Planetary Companions within 25 pc 1 Hirsch Lea A. Rosenthal Lee Fulton Benjamin J. Howard Andrew W. Ciardi David R. Marcy Geoffrey W. Nielsen Eric L. Petigura Erik A. de Rosa Robert J. Isaacson Howard Weiss Lauren M. Sinukoff Evan Macintosh Bruce The Astronomical Journal 2021 161 3 134 . 10.3847/1538-3881/abd639 2012.09190 2021AJ....161..134H 229297873 free Laliotis Katherine Burt Jennifer A. etal February 2023 Doppler Constraints on Planetary Companions to Nearby Sun-like Stars: An Archival Radial Velocity Survey of Southern Targets for Proposed NASA Direct Imaging Missions The Astronomical Journal 165 4 176 10.3847/1538-3881/acc067 2302.10310 2023AJ....165..176L free External links James B. Kaler 18 Scorpii Stars University of Illinois http://stars.astro.illinois.edu/sow/18sco.html 2012-03-06 NASA article on 18 Scorpii 18 Scorpii entry in the stellar database Astronomers Measure Sun-Like Brightness Changes of the Solar Twin, 18 Scorpii High-precision abundances of elements in solar twin stars. Trends with stellar age and elemental condensation temperature Nissen P. E. Astronomy & Astrophysics 579 52 A52 15 July 2015 10.1051/0004-6361/201526269 free 2015A&A...579A..52N 1504.07598 56276093 Scorpii, 18 Scorpii, 18 Category:Scorpius BD-07 4242 Scorpii, 18 0616 146233 079672 6060 Category:G2V stars