18 Monocerotis
Star in the constellation Monoceros
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18 Monocerotis is a binary star system located about halfway from Orion's Belt to Procyon,[6] in the equatorial constellation of Monoceros.[11] It is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.47,[2] and is positioned around 370[1] light years away from the Sun based on parallax. The system is receding from the Earth with a heliocentric radial velocity of +11 km/s.[4]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Monoceros |
| Right ascension | 06h 47m 51.64752s[1] |
| Declination | +02° 24â² 43.7737â³[1] |
| Apparent magnitude (V) | 4.47[2] |
| Characteristics | |
| Spectral type | K0+IIIaBa0.2[3] |
| UâB color index | +1.04[2] |
| BâV color index | +1.11[2] |
| Astrometry | |
| Radial velocity (Rv) | +11.29[4] km/s |
| Proper motion (μ) | RA: -16.898[1] mas/yr Dec.: -16.229[1] mas/yr |
| Parallax (Ï) | 8.0947±0.2385 mas[1] |
| Distance | 400 ± 10 ly (124 ± 4 pc) |
| Absolute magnitude (MV) | -0.78[5] |
| Orbit[6][7] | |
| Primary | 18 Monocerotis A |
| Name | 18 Monocerotis B |
| Period (P) | 1760.9±1.9 d |
| Semi-major axis (a) | 6.63 mas |
| Eccentricity (e) | 0.40±0.04 |
| Inclination (i) | 96.25° |
| Longitude of the node (Ω) | 47.63° |
| Periastron epoch (T) | 2441942.5 |
| Argument of periastron (Ï) (secondary) | 172±6° |
| Details | |
| 18 Mon A | |
| Radius | 26.95+1.56 â0.81[1] Râ |
| Luminosity | 311.2±10.5[1] Lâ |
| Surface gravity (log g) | 2.59[8] cgs |
| Temperature | 4,750[9] K |
| Metallicity [Fe/H] | -0.03[5] dex |
| Rotational velocity (v sin i) | < 2.0[10] km/s |
| Other designations | |
| 18 Mon, BD+02°1397, FK5 258, GC 8892, HD 49293, HIP 32578, HR 2506, SAO 114428[11] | |
| Database references | |
| SIMBAD | data |
It is reported as a single-lined spectroscopic binary with an orbital period of 1,760.9 days (4.8 years) and an eccentricity of 0.4.[6] The visible component is an aging K-type giant star with a stellar classification of K0+IIIaBa0.2,[3] showing a slight overabundance of barium. The spectrum displays strong violet lines of CN.[6] With the supply of hydrogen at its core exhausted, this star has expanded to 27[1] times the radius of the Sun. It is radiating 311[1] times the luminosity of the Sun from its swollen photosphere at an effective temperature of 4,750 K.[9]