12 Ophiuchi

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**12 Ophiuchi**
Observation data Equinox J2000
Constellation	Ophiuchus
Right ascension	16^h 36^m 21.4493^s
Declination	-02° 19′ 28.501″
Apparent magnitude (V)	5.76
Characteristics
Spectral type	K2 V
U-B color index	0.50
B-V color index	0.82
Variable type	BY Draconis
Astrometry
Radial velocity (R_v)	-15.4 km/s
Proper motion (μ)	RA: 455.23 mas/yr Dec.: -307.64 mas/yr
Parallax (π)	102.27 ± 0.85 mas
Distance	31.9 ± 0.3 ly (9.78 ± 0.08 pc)
Details
Mass	? M_☉
Radius	? R_☉
Luminosity	? L_☉
Temperature	5,300^[1] K
Metallicity	102 % Sun^[1]
Rotation	21.3 days^[2]
Age	? years
Other designations
12 Oph, V2133 Oph, GJ 631, HR 6171, BD -01 3220, HD 149661, LHS 3224, LTT 6632, GCTP 3773.00, SAO 141269, FK5 1433, HIP 81300.
Database references
SIMBAD	data
ARICNS	data

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.^[3]

This star is categorized as a BY Draconis variable, with variable star designation V2133. The variability of this star 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.^[4] Measurements of the long-term variability of this star 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.^[5]

The abundance of heavy elements (elements heavier than Helium) in this star is nearly identical to the Sun. The surface gravity is equal to $log(g) = 4.6$ , which is somwhat higher than the Sun's.^[1] The space velocity of this star is 30 km/s relative to the solar system. The high rotation period and active chromosphere are indicative of a relatively young star.^[6]^[7]

[edit] References

^ ^a ^b ^c C. Flynn, O. Morel (1997). "Metallicities and kinematics of G and K dwarfs". Monthly Notices of the Royal Astronomical Society 286 (3): 617-625.
^ (1999) "Lifetime of Surface Features and Stellar Rotation: A Wavelet Time-Frequency Approach". The Astrophysical Journal 510 (2): L135-L138.
^ H. J. Habing, P. Bouchet, C. Dominik, T, Encrenaz, A. Heske, M. Jourdain de Muizon, M. F. Kessler, R. Laureijs, K. Leech, L. Metcalfe, A. Salama, R. Siebenmorgen, N. Trams, C. Waelkens, L. B. F. M. Waters (1996). "First results from a photometric infrared survey for Vega-like disks around nearby main-sequence stars.". Astronomy and Astrophysics 315: L233-L236.
^ J. D. Dorren, E. F. Guinan, E. F. (1982). "Evidence for starspots on single solar-like stars". Astronomical Journal 87: 1546-1557.
^ H-K Project: Activity Cycles. Mount Wilson Observatory. Retrieved on December 4, 2006.
^ H. J. Rocha-Pinto, B. V. Castilho, W. J. Maciel (2002). "Chromospherically young, kinematically old stars". Astronomy & Astrophysics 384: 912-924.
^ 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.