18 Draconis
Star in the constellation Draco
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18 Draconis is a likely binary star[7] system in the northern circumpolar constellation of Draco. With an apparent visual magnitude of 4.84,[2] it is just bright enough to be faintly visible to the naked eye. The distance to this system, as estimated from an annual parallax shift of 4.5 mas,[1] is roughly 720 light years (220 parsecs). It is moving closer to the Sun with a heliocentric radial velocity of â1.4 km/s,[5] and is a probable member of the Sirius stream of co-moving stars.[8]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Draco |
| Right ascension | 16h 40m 55.11952s[1] |
| Declination | +64° 35â² 20.5824â³[1] |
| Apparent magnitude (V) | 4.84[2] |
| Characteristics | |
| Evolutionary stage | horizontal branch[3] |
| Spectral type | K0 III CNâ0.5 CHâ2 Ca1[4] |
| BâV color index | 1.212±0.003[2] |
| Astrometry | |
| Radial velocity (Rv) | â1.37±0.09[5] km/s |
| Proper motion (μ) | RA: â0.599[1] mas/yr Dec.: â17.436[1] mas/yr |
| Parallax (Ï) | 4.5045±0.1730 mas[1] |
| Distance | 720 ± 30 ly (222 ± 9 pc) |
| Absolute magnitude (MV) | â1.92[2] |
| Details[3] | |
| Mass | 3.81±0.38 Mâ |
| Radius | 46.83±1.74 Râ |
| Luminosity | 786.7±56.3 Lâ |
| Surface gravity (log g) | 1.69±0.06 cgs |
| Temperature | 4,471±23 K |
| Metallicity [Fe/H] | â0.13±0.10 dex |
| Age | 280±80 Myr |
| Other designations | |
| g Dra, 18 Dra, BD+64°1145, FK5 3326, HD 151101, HIP 81660, HR 6223, SAO 17188[6] | |
| Database references | |
| SIMBAD | data |
The visible component has a stellar classification of K0 III CNâ0.5 CHâ2 Ca1,[4] indicating it is an evolved K-type giant star with some abundance peculiarities in its atmosphere. At the age of around 280 million years, it is most likely (99% chance) on the horizontal branch.[3] It is a barium star, which suggests it may have a degenerate white dwarf companion from which it accreted materials during an earlier stage of its evolution.[9][7] 18 Dra has an estimated 3.8 times the mass of the Sun and has expanded to 47 times the Sun's radius. The star is radiating 787 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,471 K.[3]