4 Ursae Minoris
Binary star system in the constellation Ursa Minor
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4 Ursae Minoris is a binary star[6] system in the northern circumpolar constellation Ursa Minor. It is faintly visible to the naked eye with an apparent visual magnitude of 4.80.[2] Based upon an annual parallax shift of 7.14±0.42 mas[1] as seen from Earth's orbit, it is located roughly 460 light years from the Sun. It is moving further away with a heliocentric radial velocity of +5.9 km/s.[5]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ursa Minor |
| Right ascension | 14h 08m 50.92654s[1] |
| Declination | +77° 32′ 51.0466″[1] |
| Apparent magnitude (V) | 4.80[2] |
| Characteristics | |
| Spectral type | K3-IIIb Fe-0.5[3] |
| B−V color index | 1.368[4] |
| Astrometry | |
| Radial velocity (Rv) | +5.86±0.10[5] km/s |
| Proper motion (μ) | RA: −30.45[1] mas/yr Dec.: +32.85[1] mas/yr |
| Parallax (π) | 7.14±0.42 mas[1] |
| Distance | 460 ± 30 ly (140 ± 8 pc) |
| Absolute magnitude (MV) | −1.06[4] |
| Orbit[6] | |
| Period (P) | 605.8 d |
| Semi-major axis (a) | 6.5 mas[7] |
| Eccentricity (e) | 0.137±0.012 |
| Inclination (i) | 136.0±5.1[7]° |
| Longitude of the node (Ω) | 325.5±2.8° |
| Periastron epoch (T) | 2,438,901.7±8.5 JD |
| Argument of periastron (ω) (secondary) | 311.8±5.2° |
| Semi-amplitude (K1) (primary) | 12.65±0.16 km/s |
| Details | |
| 4 UMi A | |
| Radius | 28[8] R☉ |
| Luminosity | 436.72[2] L☉ |
| Surface gravity (log g) | 1.73±0.45[9] cgs |
| Temperature | 4,165±48[9] K |
| Metallicity [Fe/H] | −0.19±0.11[9] dex |
| Other designations | |
| 4 UMi, BD+78°478, FK5 524, HD 124547, HIP 69112, HR 5321, SAO 7958[10] | |
| Database references | |
| SIMBAD | data |
This is a single-lined spectroscopic binary star system with an orbital period of 1.66 years and an eccentricity of 0.14.[7][6] The primary is a red giant of spectral type K3-IIIb Fe-0.5,[3] a star that has used up its core hydrogen and is expanding. The suffix notation indicates the spectrum displays a mild underabundance of iron for a star of its type. It has expanded to around 28[8] times the Sun's radius and is radiating 437[2] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,165 K.[9]
In Chinese astronomy, this star is named Hougong, the imperial concubine or empress. It forms the asterism Beiji (Northern Pole) with γ Ursae Minoris, β Ursae Minoris, 5 Ursae Minoris, and Σ 1694.[11]