Polaris
Proper names: Polaris, Alpha Ursae Minoris, 1 Ursae Minoris, The North Star, The Pole Star
Catalog numbers:
Henry Draper (HD) 8890, Bonner Durchmusterung (BD) +88°8, Hoffleit Bright Star (HR) 424, Smithsonian Astrophysical Observatory (SAO) 308, Fifth Fundamental Catalogue (FK5) 907, Aitken Double Star (ADS) 1477, Hipparcos Input Catalog (HIC) 11767
Heavy element abundance: 106% of Sol
Standard error in heavy element abundance: 5%
Source for heavy element abundance: Strobel [Fe/H] Determinations
Arity: binary
Points of interest:
In 1994, Polaris A's variability disappeared altogether, only to return again in 1995. An unseen companion is suspected to be orbiting close to Polaris A (hence its designation as a close-orbiting binary pair below), with a period of 30.5 years, a semi-major axis of 3.1 A.U.s, and an eccentricity of 0.64, giving it a periastron gap about 5 times narrower than its apastron gap. This unseen companion would have to be at least 6 magnitudes dimmer than Polaris A. Periastron for the unseen companion happened in 1928.
Right Ascension and Declination: 2h31m48.704s, +89°15'50.72" (epoch 2000.0)
Distance from Sol: 431 light-years (132 parsecs)
Standard error in distance: 5.9701%
Source for distance: Hipparcos
Celestial (X,Y,Z) coordinates in ly: 4.37, 3.41, 431
Galactic (X,Y,Z) coordinates in ly: -212, 322, 194
Proper motion: 0.0409 arcsec/yr (111.5° from north)
Radial Velocity: -17.4 km/sec
Source for proper motion and radial velocity: Hipparcos Input Catalog
Galactic (U,V,W) velocity components in km/s: -12.4, -27.7, -6.21
What do all these fields mean?
Data for A and B's orbit around one other:
Combined absolute visual magnitude: -3.51
Combined visual luminosity: 2210 x Sol
Observed Separation: 2646 A.U.s
Source for orbit data: Burnham's Celestial Handbook
As seen from A:
B would appear as magnitude -11.67
As seen from B:
A would appear as magnitude -17.97
Component A:
NOTE: This star is actually a close-orbiting binary pair. The data below are for both sub-components of the pair combined.
Spectral class: F7
Luminosity Class: Ib-II
Apparent visual magnitude: +2.10 (increasing to +1.90)
Absolute visual magnitude: -3.51 (increasing to -3.71)
Visual luminosity: 2204 x Sol (increasing to 2649 x Sol)
Variable type: delta Cephei (pulsating variable)
Period of variability: 3.9696 days
Color indices: B-V= +0.60, U-B= +0.38, R-I= +0.31
Diameter: 43.9 x Sol
Source for diameter: Apparent Diameters and Absolute Radii of Stars (Fracassini+ 1988)
Comfort Zone (visual): 46.9 A.U.s
Angular size of star in sky in CZ: 0.498884 degrees
Component B:
Spectral class: F3
Luminosity Class: V
Apparent visual magnitude: +8.40
Absolute visual magnitude: +2.79
Visual luminosity: 6.65 x Sol
Mass: 1.5 x Sol
Comfort Zone (visual): 2.58 A.U.s
Orbital period in CZ: 3.38222 years
Tidal index in CZ: 0.087417
Data for this star system were most recently updated on 4-April-2001.