Mu Draconis
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Draco |
| Right ascension | 17h 05m 20.12403s |
| Declination | +54° 28′ 12.0994″ |
| Apparent magnitude (V) | 4.92 (5.66 / 5.69) |
| Characteristics | |
| Spectral type | F7V |
| U−B color index | −0.01 |
| B−V color index | +0.47 |
| Astrometry | |
| Radial velocity (Rv) | −17.30±0.5 km/s |
| Proper motion (μ) | RA: −58.16 mas/yr Dec.: +67.87 mas/yr |
| Parallax (π) | 36.45±0.46 mas |
| Distance | 89 ± 1 ly (27.4 ± 0.3 pc) |
| Absolute magnitude (MV) | +2.73 |
| Orbit | |
| Primary | μ Dra A |
| Companion | μ Dra B |
| Period (P) | 812.0±70.5 yr |
| Semi-major axis (a) | 4.48±0.03″ |
| Eccentricity (e) | 0.5139±0.029 |
| Inclination (i) | 142.2±1.3° |
| Longitude of the node (Ω) | 282.85±0.80° |
| Periastron epoch (T) | 1946.19±0.72 |
| Argument of periastron (ω) (secondary) | 193.31±0.083° |
| Details | |
| μ Dra A | |
| Mass | 1.35 M☉ |
| Metallicity [Fe/H] | −0.01 dex |
| μ Dra B | |
| Mass | 1.30 M☉ |
| Age | 2.2 Gyr |
| Other designations | |
| 21 Draconis, GJ 9584, BD+54°1857, SAO 30239, HIP 83608 | |
| A: Alrakis, HR 6370, HD 154906 | |
| B: HR 6369, HD 154905 | |
| Database references | |
| SIMBAD | μ Dra |
| μ Dra A | |
| μ Dra B | |
Mu Draconis (μ Draconis, abbreviated Mu Dra, μ Dra) is a multiple star system near the head of the constellation of Draco. With a combined magnitude of 4.92, it is visible to the naked eye. Based on parallax estimates by the Hipparcos spacecraft, it is located approximately 89 light-years from the Sun.
The system consists of a single primary star (designated Mu Draconis A, officially named Alrakis /ælˈreɪkɪs/ from the traditional name of the system), a secondary binary pair (Mu Draconis B) and a further single star (C). B's two components are designated Mu Draconis Ba and Bb.
Mu Draconis A and Ba are nearly identical F-type main-sequence stars, with masses of 1.35 M☉ and 1.30 M☉, respectively. Both have the spectral class of F5V, and have similar apparent magnitude, at 5.66 and 5.69, respectively. The secondary, Mu Draconis B, has a drifting radial velocity, and is itself a spectroscopic binary with an orbital period of 2,270 days. The distance between both stars is 2 arcseconds, so a telescope with a diameter of at least 6 centimetres is necessary to see them separate. The smaller component, Mu Draconis Bb, has a mass of 0.2 M☉. Mu Draconis C is a 14th magnitude common-proper-motion companion 13.2" away from the bright pair, with a mass of 0.29 M☉.