Omicron Draconis
Variable star in the constellation Draco
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Omicron Draconis (Latinised as ο Draconis, abbreviated to ο Dra) is a giant star in the constellation Draco located 322.93 light years from the Earth. Its path in the night sky is circumpolar for latitudes greater than 31o north, meaning the star never rises or sets when viewed in the night sky.
  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Draco |
| Right ascension | 18h 51m 12.09530s[1] |
| Declination | +59° 23′ 18.0627″[1] |
| Apparent magnitude (V) | 4.65[2] |
| Characteristics | |
| Spectral type | G9III[3] |
| U−B color index | +1.19[2] |
| Variable type | RS CVn + eclipsing[4] |
| Astrometry | |
| Radial velocity (Rv) | −19.52[5] km/s |
| Proper motion (μ) | RA: 77.47[1] mas/yr Dec.: 25.37[1] mas/yr |
| Parallax (π) | 9.54±0.21 mas[1] |
| Distance | 106.8[4] pc |
| Absolute magnitude (MV) | −0.344[6] |
| Orbit[4] | |
| Period (P) | 138.444±0.003 days |
| Semi-major axis (a) | 0.00651±0.00003″ |
| Eccentricity (e) | 0.158±0.003 |
| Inclination (i) | 89.6±0.3° |
| Longitude of the node (Ω) | 22.9±0.2° |
| Periastron epoch (T) | 2454983.0±0.2 |
| Argument of periastron (ω) (secondary) | 293.0±0.6° |
| Semi-amplitude (K1) (primary) | 23.42±0.05 km/s |
| Semi-amplitude (K2) (secondary) | 32.0±0.4 km/s |
| Details | |
| ο Dra A | |
| Mass | 1.35[4] M☉ |
| Radius | 25.1[4] R☉ |
| Luminosity | 220[4] L☉ |
| Surface gravity (log g) | 1.769[4] cgs |
| Temperature | 4,400[7] K |
| Metallicity [Fe/H] | −0.5[3] dex |
| Rotation | 79[4] |
| Rotational velocity (v sin i) | 20.0[6] km/s |
| Age | 3.0[4] Gyr |
| ο Dra B | |
| Mass | 0.99[4] M☉ |
| Radius | 1.0[4] R☉ |
| Luminosity | 1.3[4] L☉ |
| Surface gravity (log g) | 4.43[4] cgs |
| Temperature | 6,000[4] K |
| Other designations | |
| Omicron Draconis, 47 Draconis, HR 7125, HD 175306, HIP 92512, BD+59°1925 | |
| Database references | |
| SIMBAD | data |
This is a single-lined spectroscopic binary system,[7] but the secondary has been detected using interferometry. It is an RS Canum Venaticorum variable system with eclipses. The total amplitude of variation is only a few hundredths of a magnitude.[4][8] The secondary star is similar to the Sun, presumably a main-sequence star, while the primary is a giant star 25 times larger than the Sun and two hundred times more luminous.
Identities as pole star
Omicron Draconis can be considered the north pole star of Mercury, as it is the closest star to Mercury's north celestial pole.[9] In addition to that, this star is currently the Moon's north pole star, which occurs once every 18.6 years.[10] The pole star status changes periodically, because of the precession of the Moon's rotational axis.