12 Ophiuchi

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12 Ophiuchi
Observation data
Epoch J2000      Equinox J2000
Constellation Ophiuchus
Right ascension 16h 36m 21.44979s[1]
Declination –02° 19′ 28.5195″[1]
Apparent magnitude (V) 5.77[2]
Spectral type K2 V
U−B color index +0.50
B−V color index +.82
Variable type BY Draconis
Radial velocity (Rv) –15.4 km/s
Proper motion (μ) RA: +456.04[1] mas/yr
Dec.: –309.63[1] mas/yr
Parallax (π) 102.55 ± 0.40[1] mas
Distance 31.8 ± 0.1 ly
(9.75 ± 0.04 pc)
Absolute magnitude (MV) 5.57 ± 0.05[2]
Mass 0.91[2] M
Radius 0.84 ± 0.03[2] R
Luminosity 0.39 L
Luminosity (bolometric) 0.45 L
Surface gravity (log g) 4.59 ± 0.10[2] cgs
Temperature 5,300[3] K
Metallicity 102% Sun[3]
Metallicity [Fe/H] +0.04 ± 0.07[2] dex
Rotation 21.3 days[4]
Rotational velocity (v sin i) 2.4 ± 1.0[2] km/s
Age 1.0–1.9[5] Gyr
Other designations
12 Oph, BD-01 3220, FK5 1433, GCTP 3773.00, GJ 631, HD 149661, HIP 81300, HR 6171, LHS 3224, LTT 6632, V2133 Oph, SAO 141269.
Database references

12 Ophiuchi is a variable star in the constellation Ophiuchus. No companions have yet been detected in orbit around this star, and it remains uncertain whether or not it possesses a dust ring.[6]

This star is categorized as a BY Draconis variable, with variable star designation V2133. The variability is attributed to large-scale magnetic activity on the chromosphere (in the form of starspots) combined with a rotational period that moved the active regions into (and out of) the line of sight. This results in low amplitude variability of 12 Ophiuchi's luminosity. The star also appears to display rapid variation in luminosity, possibly due to changes in the starspots.[7] Measurements of the long-term variability show two overlapping cycles of starspot activity (compared to the Sun's single, 11-year cycle.) The periods of these two cycles are 4.0 and 17.4 years.[8]

This star is among the top 100 target stars for NASA's planned Terrestrial Planet Finder mission [1]. However, the mission is now postponed indefinitely.

Its abundance of heavy elements (elements heavier than helium) is nearly identical to that of the Sun. The surface gravity is equal to \log(g) = 4.6, which is somewhat higher than the Sun's.[3] The space velocity is 30 km/s relative to the solar system. The high rotation period and active chromosphere are indicative of a relatively young star.[9][10]


  1. ^ a b c d e van Leeuwen, F. (November 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 
  2. ^ a b c d e f g Fuhrmann, Klaus (February 2008), "Nearby stars of the Galactic disc and halo - IV", Monthly Notices of the Royal Astronomical Society 384 (1): 173–224, Bibcode:2008MNRAS.384..173F, doi:10.1111/j.1365-2966.2007.12671.x 
  3. ^ a b c Flynn, C.; Morel, O. (1997), "Metallicities and kinematics of G and K dwarfs", Monthly Notices of the Royal Astronomical Society 286 (3): 617–625, arXiv:astro-ph/9609017, Bibcode:1996astro.ph..9017F, doi:10.1093/mnras/286.3.617 
  4. ^ Soon, Willie; Frick, Peter; Baliunas, Sallie (1999), "Lifetime of Surface Features and Stellar Rotation: A Wavelet Time-Frequency Approach", The Astrophysical Journal 510 (2): L135–L138, arXiv:astro-ph/9811114, Bibcode:1999ApJ...510L.135S, doi:10.1086/311805 
  5. ^ Mamajek, Eric E.; Hillenbrand, Lynne A. (November 2008), "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics", The Astrophysical Journal 687 (2): 1264–1293, arXiv:0807.1686, Bibcode:2008ApJ...687.1264M, doi:10.1086/591785 
  6. ^ H. J. Habing; P. Bouchet; C. Dominik, T; Encrenaz, A. Heske; M. Jourdain de Muizon; M. F. Kessler et al. (1996). "First results from a photometric infrared survey for Vega-like disks around nearby main-sequence stars.". Astronomy and Astrophysics 315: L233–L236. Bibcode:1996A&A...315L.233H. 
  7. ^ J. D. Dorren; E. F. Guinan; E. F. (1982). "Evidence for starspots on single solar-like stars". Astronomical Journal 87: 1546–1557. Bibcode:1982AJ.....87.1546D. doi:10.1086/113245. 
  8. ^ "H-K Project: Activity Cycles". Mount Wilson Observatory. Retrieved 2006-12-04. 
  9. ^ H. J. Rocha-Pinto; B. V. Castilho; W. J. Maciel (2002). "Chromospherically young, kinematically old stars". Astronomy & Astrophysics 384 (3): 912–924. arXiv:astro-ph/0112452. Bibcode:2002A&A...384..912R. doi:10.1051/0004-6361:20011815. 
  10. ^ G. F. Porto de Mello; E. F. del Peloso; L. Ghezzi (2006). "Astrobiologically interesting stars within 10 parsecs of the Sun". Astrobiology 6 (2): 308–331. arXiv:astro-ph/0511180. Bibcode:2006AsBio...6..308P. doi:10.1089/ast.2006.6.308. PMID 16689649. 

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