12 Ophiuchi

12 Ophiuchi

Observation data Epoch J2000      Equinox J2000
Constellation	Ophiuchus
Right ascension	16h 36m 21.44979s
Declination	–02° 19′ 28.5195″
Apparent magnitude (V)	5.77
Characteristics
Spectral type	K2 V
U−B color index	+0.50
B−V color index	+.82
Variable type	BY Draconis
Astrometry
Radial velocity (Rv)	–15.4 km/s
Proper motion (μ)	RA: +456.04 mas/yr Dec.: –309.63 mas/yr
Parallax (π)	102.55 ± 0.40 mas
Distance	31.8 ± 0.1 ly (9.75 ± 0.04 pc)
Absolute magnitude (MV)	5.57 ± 0.05
Details
Mass	0.91 M☉
Radius	0.84 ± 0.03 R☉
Luminosity	0.39 L☉
Luminosity (bolometric)	0.45 L☉
Surface gravity (log g)	4.59 ± 0.10 cgs
Temperature	5,300 K
Metallicity	102% Sun
Metallicity [Fe/H]	+0.04 ± 0.07 dex
Rotation	21.3 days
Rotational velocity (v sin i)	2.4 ± 1.0 km/s
Age	1.0–1.9 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
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.

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. 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.

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. 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.