18 Scorpii
| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Scorpius |
| Right ascension | 16h 15m 37.26946s[1] |
| Declination | –08° 22′ 09.9870″[1] |
| Apparent magnitude (V) | 5.503[2] |
| Characteristics | |
| Spectral type | G2 Va |
| U−B color index | +0.18[3] |
| B−V color index | +0.64[3] |
| Variable type | Sun-like[4] |
| Astrometry | |
| Radial velocity (Rv) | +11.6[2] km/s |
| Proper motion (μ) | RA: 230.77[1] mas/yr Dec.: -495.53[1] mas/yr |
| Parallax (π) | 71.94 ± 0.37[1] mas |
| Distance | 45.3 ± 0.2 ly (13.90 ± 0.07 pc) |
| Absolute magnitude (MV) | 4.77[2] |
| Details | |
| Mass | 1.02 ± 0.03[5] M☉ |
| Radius | 1.010 ± 0.009[5] R☉ |
| Luminosity | 1.08 L☉ |
| Surface gravity (log g) | 4.45[6] |
| Temperature | 5,818[6] K |
| Metallicity [Fe/H] | 0.04[6] dex |
| Rotation | 23 days |
| Age | (4.1–5.3) × 109[7] years |
| Other designations | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
18 Scorpii is a star located some 45.3 light years from Earth at the northern edge of the Scorpius constellation.
18 Scorpii has many physical properties in common with the Sun. Cayrel de Strobel (1996) included it in her review of the stars most similar to the Sun,[8] and Porto de Mello & da Silva (1997) identified it as a solar twin.[9] Some scientists therefore believe the prospects for life in its vicinity are good.
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[edit] Star characteristics
18 Scorpii is a main sequence star of spectral and luminosity type G2 Va.[9] 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.[6][10] 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.[5]
According to Lockwood (2002), it has a temporal photometric behavior very similar to the Sun.[11] Its brightness variation over its entire activity cycle is 0.09%, about the same as the Sun's brightness variations during recent solar cycles.[12] 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.[13] The estimated period for the activity cycle of 18 Scorpii is about seven years,[4] which is significantly shorter than the Sun's, and its overall chromospheric activity level is noticeably higher.[12][14]
18 Scorpii is a solitary star, and radial velocity measurements have not yet revealed the presence of planets orbiting it.[15]
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.[16]
[edit] Prospects for life
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.
[edit] See also
[edit] References
- ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, Bibcode 2007A&A...474..653V, doi:10.1051/0004-6361:20078357
- ^ a b c Nordström, B. et al. (May 2004), "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14 000 F and G dwarfs", Astronomy and Astrophysics 418: 989–1019, arXiv:astro-ph/0405198, Bibcode 2004A&A...418..989N, doi:10.1051/0004-6361:20035959
- ^ a b c "18 Sco -- Variable Star", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=18+Sco, retrieved 2011-10-13 The ubv information is per Compilation of Eggen's UBV data, transformed to UBV (unpublished) 1986. See the Measurements section.
- ^ a b Hall, Jeffrey C. et al. (July 2009), "The Activity and Variability of the Sun and Sun-Like Stars. II. Contemporaneous Photometry and Spectroscopy of Bright Solar Analogs", The Astronomical Journal 138 (1): 312–322, Bibcode 2009AJ....138..312H, doi:10.1088/0004-6256/138/1/312
- ^ a b c Bazot, M. et al. (February 2011), "The radius and mass of the close solar twin 18 Scorpii derived from asteroseismology and interferometry", Astronomy and Astrophysics 526, Bibcode 2011A&A...526L...4B, doi:10.1051/0004-6361/201015679
- ^ a b c d 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
- ^ Mamajek, Eric E.; Hillenbrand, Lynne A. (2008), "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics", The Astrophysical Journal 687 (2): 1264–1293, Bibcode 2008ApJ...687.1264M, doi:10.1086/591785
- ^ Cayrel de Strobel, G. (1996), "Stars Resembling the Sun", The Astronomy and Astrophysics Review 7 (3): 243–288, Bibcode 1996A&ARv...7..243C, doi:10.1007/s001590050006
- ^ a b Porto de Mello, G. F.; da Silva, L. (1997), "HR 6060: The Closest Ever Solar Twin?", The Astrophysical Journal 482 (2): L89–L92, Bibcode 1997ApJ...482L..89P, doi:10.1086/310693
- ^ A metallicity of [Fe/H] = 1.04 dex indicates that the star has 100.04 = 1.096, or 110% of the abundance of elements heavier than helium, compared to the Sun.
- ^ Lockwood, G. W. et al. (May 2002), "Gauging the Sun: Comparative photometric and magnetic activity measurements of sunlike stars, 1984-2001" (PDF), Bulletin of the American Astronomical Society 34: 651, Bibcode 2002AAS...200.0709L, http://schwab.tsuniv.edu/papers/baas/aas2002poster.pdf
- ^ a b Hall, J. C.; Lockwood, G. W. (2007), "The Sun-Like Activity of the Solar Twin 18 Scorpii", The Astronomical Journal 133 (5): 2206–2008, arXiv:astro-ph/0703450, Bibcode 2007AJ....133.2206H, doi:10.1086/513195
- ^ Petit, P. et al. (2008), "Toroidal versus poloidal magnetic fields in Sun-like stars: a rotation threshold", Monthly Notices of the Royal Astronomical Society 388 (1): 80, Bibcode 2008MNRAS.388...80P, doi:10.1111/j.1365-2966.2008.13411.x
- ^ Hall, Jeffrey C.; Lockwood, G. W. (2000), "Evidence of a Pronounced Activity Cycle in the Solar Twin 18 Scorpii", The Astrophysical Journal 545 (2): L43–L45, Bibcode 2000ApJ...545L..43H, doi:10.1086/317331
- ^ Marcy, G. W., et al. (2005). "Five New Extrasolar Planets". The Astrophysical Journal 619 (1): 570–584. Bibcode 2005ApJ...619..570M. doi:10.1086/426384.
- ^ Meléndez, J.; Ramírez, I. (2007), "HIP 56948: A Solar Twin with a Low Lithium Abundance", The Astrophysical Journal 669 (2): L89–L92, Bibcode 2007ApJ...669L..89M, doi:10.1086/523942
[edit] External links
- NASA article on 18 Scorpii
- 18 Scorpii entry in the stellar database
- Astronomers Measure Sun-Like Brightness Changes of the Solar Twin, 18 Scorpii
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