39 Draconis
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Draco |
| Right ascension | 18h 23m 54.60641s |
| Declination | +58° 48′ 02.6446″ |
| Apparent magnitude (V) | 5.034 (5.06 + 8.07) |
| Characteristics | |
| Spectral type | A1V + F5V |
| U−B color index | +0.06 |
| B−V color index | +0.10 |
| Astrometry | |
| Radial velocity (Rv) | −24.53±0.23 km/s |
| Proper motion (μ) | RA: −37.82 mas/yr Dec.: +61.60 mas/yr |
| Parallax (π) | 17.71±0.35 mas |
| Distance | 184 ± 4 ly (56 ± 1 pc) |
| Absolute magnitude (MV) | 1.31 / 4.32 |
| Orbit | |
| 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 M☉ |
| Radius | 2.3 R☉ |
| Surface gravity (log g) | 4.05 ± 0.07 cgs |
| Temperature | 8710 K |
| 39 Dra B | |
| Mass | 1.18 M☉ |
| Other designations | |
| b Dra, 39 Dra, BD+58°1809, HD 170073, HIP 90156, HR 6923, SAO 30949 | |
| Database references | |
| SIMBAD | 39 Dra |
| 39 Dra A | |
| 39 Dra B | |
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. Parallax measurements made by the Hipparcos spacecraft put it at a distance of 184 light-years, or 56 parsecs away from the Sun. The system is moving closer to the Earth with a heliocentric radial velocity of -24.5 km/s.
The two components of 39 Draconis have an angular separation of 6.621″ and take almost 4,000 years to orbit each other. 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 The secondary is a magnitude 8.07 F-type main-sequence star, and has 1.18 times the mass of the Sun.
The 8th-magnitude star HD 238865 is listed in double star catalogues as component C. It is separated from the other two stars by 90″ and lies at about the same distance. It is itself a spectroscopic binary with an F8 primary and a red dwarf secondary orbiting every 2.7 days.