39 Draconis is a wide binary star system in the northern circumpolar constellation of Draco. It has the Bayer designation b Draconis, while 39 Draconis is the Flamsteed designation. This system is visible to the naked eye as a dim, white-hued point of light with an apparent visual magnitude of 5.0.[2] Parallax measurements made by the Hipparcos spacecraft put it at a distance of 184 light-years, or 56 parsecs away from the Sun.[1] The system is moving closer to the Earth with a heliocentric radial velocity of -24.5 km/s.[6]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Draco |
| Right ascension | 18h 23m 54.60641s[1] |
| Declination | +58° 48′ 02.6446″[1] |
| Apparent magnitude (V) | 5.034[2] (5.06 + 8.07)[3] |
| Characteristics | |
| Spectral type | A1V + F5V[4] |
| U−B color index | +0.06[5] |
| B−V color index | +0.10[5] |
| Astrometry | |
| Radial velocity (Rv) | −24.53±0.23[6] km/s |
| Proper motion (μ) | RA: −37.82[1] mas/yr Dec.: +61.60[1] mas/yr |
| Parallax (π) | 17.71 ± 0.35 mas[1] |
| Distance | 184 ± 4 ly (56 ± 1 pc) |
| Absolute magnitude (MV) | 1.31 / 4.32[7] |
| Orbit[3] | |
| Period (P) | 3962.50 ± 209.26 yr |
| Semi-major axis (a) | 6.621 ± 0.325″ |
| Eccentricity (e) | 0.553 ± 0.005 |
| Inclination (i) | 107.7 ± 0.12° |
| Longitude of the node (Ω) | 179.9 ± 0.10° |
| Periastron epoch (T) | 5671.40 ± 12.08 |
| Argument of periastron (ω) (secondary) | 128.0 ± 2.18° |
| Details | |
| 39 Dra A | |
| Mass | 2.12[7] M☉ |
| Radius | 2.3[8] R☉ |
| Surface gravity (log g) | 4.05 ± 0.07[8] cgs |
| Temperature | 8710[8] K |
| 39 Dra B | |
| Mass | 1.18[7] M☉ |
| Other designations | |
| Database references | |
| SIMBAD | 39 Dra |
| 39 Dra A | |
| 39 Dra B | |
The two components of 39 Draconis have an angular separation of 6.621″ and take almost 4,000 years to orbit each other.[3] The primary star is an early A-type main-sequence star, having 2.12 times the mass of the Sun with a visual magnitude of 5.06[3] The secondary is a magnitude 8.07[3] F-type main-sequence star, and has 1.18 times the mass of the Sun.[7]
The 8th-magnitude star HD 238865 is listed in double star catalogues as component C.[9] It is separated from the other two stars by 90″ and lies at about the same distance.[10] It is itself a spectroscopic binary with an F8 primary and a red dwarf secondary orbiting every 2.7 days.[11][12]