Chi Ophiuchi, Latinized from χ Ophiuchi, is a variable star in the equatorial constellation of Ophiuchus.[13] It has a blue-white hue and is faintly visible to the naked eye with an apparent visual magnitude that fluctuates around 4.22.[3] The distance to this object, as determined from parallax measurements, is approximately 500 light years,[2] but it is moving closer to the Sun with a radial velocity of −19 km/s.[8] This star is a proper motion member of the Upper Scorpius sub-group in the Scorpius–Centaurus OB association; the nearest such co-moving association of massive stars to the Sun.[14]
Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
---|---|
Constellation | Ophiuchus |
Right ascension | 16h 27m 01.43557s[2] |
Declination | −18° 27′ 22.4500″[2] |
Apparent magnitude (V) | 4.22[3] (4.18 to 5.0)[4] |
Characteristics | |
Evolutionary stage | main sequence |
Spectral type | B2Vne[5] |
U−B color index | −0.75[6] |
B−V color index | +0.28[6] |
R−I color index | +0.22[6] |
Variable type | GCAS[4] + LERI[7] |
Astrometry | |
Radial velocity (Rv) | −19.0±2.1[8] km/s |
Proper motion (μ) | RA: −5.378[2] mas/yr Dec.: −22.308[2] mas/yr |
Parallax (π) | 6.5402 ± 0.1961 mas[2] |
Distance | 500 ± 10 ly (153 ± 5 pc) |
Absolute magnitude (MV) | −2.27[9] |
Details | |
Mass | 10.1±0.7[10] M☉ |
Radius | 4.44±0.09[11] R☉ |
Luminosity | 55,847[12] L☉ |
Surface gravity (log g) | 3.53±0.04[11] cgs |
Temperature | 30,000±300[11] K |
Rotational velocity (v sin i) | 150±3[11] km/s |
Age | 22.5±2.6[10] Myr |
Other designations | |
Database references | |
SIMBAD | data |
This is a massive Be star with a stellar classification of B2Vne,[5] where the 'n' indicates "nebulous" lines due to rapid rotation. It is spinning with a projected rotational velocity of 144 km/s. As the critical velocity for the star is 477 km/s, the inclination angle of its poles must be small; estimated as ~20°.[15] It is a Gamma Cassiopeiae variable with an amplitude of 0.15 magnitude.[16] The brightness has been measured varying from magnitude 4.18 down to 5.0.[4]
Chi Ophiuchi is 22.5 million years old with 10.1 times the mass of the Sun.[10] It has four times the Sun's radius and is radiating 56,000 times the luminosity of the Sun from its photosphere at an effective temperature of about 30,000 K. A weak magnetic field has been detected in the chromosphere of this star.[17] It is being orbited by a symmetrical disk of ejected gas extending out to 0.52 AU (112 R☉),[15] and excess radio and infrared emission has been detected from this structure.[18]
Abt and Levy (1978) cataloged Chi Ophiuchi as a single-lined spectroscopic binary with a period of 138.8 days and an eccentricity of 0.44, although the orbital elements are considered marginal.[19] Eggleton and Tokovinin (2008) list it as a single star.[20]