Alpha and Proxima Centauri

Proper names: Alpha Centauri, Alpha and Proxima Centauri, Rigil Kentaurus, Toliman
Catalog numbers:
     Gliese (Gl) 559, Cape Photographic Durchmusterung (CPD) -60°5483, Smithsonian Astrophysical Observatory (SAO) 252838, Fifth Fundamental Catalogue (FK5) 538
Age: 6520 million years
Standard error in age: 4%
Source for age: Eggenberger et al., A&A v.417 p.235
Heavy element abundance: 160% of Sol
Source for heavy element abundance: B. Edvardsson et al., "Chemical Evolution of the Galactic Disc", A&AP 275
Arity: trinary
Points of interest:
     Although the third brightest star in the system can be called "Alpha Centauri C," as per the usual naming convention, it is usually referred to as Proxima Centauri, since the dimmest star of this triplet happens to be THE closest star to our own sun. Proxima is a flare star; its flares about double the star's brightness, occurring sporadically from hour to hour. In fact, at any given moment, more than one flare may be operating. This varying brightness gave it the name "V645 Centauri" among variable star enthusiasts. Unfortunately, such flares are lethal to any life that might otherwise arise on planets in its comfort zone (if Proxima has any).
     Life on planets orbiting Alpha Centauri A or B, however, is almost as likely as life in our own star system. Since the smallest gap between A and B is 11.3 Astronomical Units, any planets closer to A or B than one-quarter of this distance (2.9 A.U.s) would be in stable orbits. Furthermore, 2.9 A.U.s is wider than the comfort zone of either of these stars, so any planets in the comfort zones of A or B would also be within the stable orbit region. These stars are young enough to have developed when the galaxy was rich with life-supporting and solid-planet-supporting heavy elements, yet old enough for any life there to have evolved into complex forms.
     Both Don C. Barry, and B. Edvardsson et al., estimated the age of this star system at 4.2 thousand-million years. The earliest estimate of this system's age, by Flannery & Ayres in the 1-April-1978 Astrophysical Journal, however, was 6 thousand-million years, which is closer to the most recent estimate.

Right Ascension and Declination: 14h39m35.88s, -60°50'7.4" (epoch 2000.0)
Distance from Sol: 4.395 light-years (1.347 parsecs)
Standard error in distance: 0.1883%
Source for distance: Hipparcos
Celestial (X,Y,Z) coordinates in ly: -1.643, -1.374, -3.838
Galactic (X,Y,Z) coordinates in ly: 3.165, -3.048, -0.0818

What do all these fields mean?

Data for A and B's orbit around one other:
Combined absolute visual magnitude: +4.08
Combined visual luminosity: 2.027 x Sol
Period: 79.92 years
Semimajor Axis: 23.60 A.U.s
Eccentricity: 0.516
Periastron distance: 11.42 A.U.s
Apastron distance: 35.78 A.U.s
Year in which periastron occurs: 1955.56
Source for orbit data: W.D. Heintz
As seen from A:
     At periastron, B would appear as magnitude -20.59
     At apastron, B would appear as magnitude -18.11
As seen from B:
     At periastron, A would appear as magnitude -21.92
     At apastron, A would appear as magnitude -19.44

Data for (A-B) and Proxima's orbit around one other:
Combined absolute visual magnitude: +4.08
Combined visual luminosity: 2.027 x Sol
Period: 500000 years
Observed Separation: 17652 A.U.s
Source for orbit data: Burnham's Celestial Handbook
As seen from (A-B):
Proxima would appear as magnitude +5.15
As seen from Proxima:
(A-B) would appear as magnitude -6.26

Component A:
Catalog numbers:
Henry Draper (HD) 128620, Luyten Half-Second (LHS) 50, Hoffleit Bright Star (HR) 5459, Hipparcos Input Catalog (HIC) 71683
Proper motion: 3.689 arcsec/yr (281.1° from north)
Radial Velocity: -26.2 km/sec
Source for proper motion and radial velocity: Gliese
Galactic (U,V,W) velocity components in km/s: -32.00, 4.165, 14.15
Spectral class: G2
Luminosity Class: V
Apparent visual magnitude: +0.01
Absolute visual magnitude: +4.36
Visual luminosity: 1.567 x Sol
Color indices: B-V= +0.64, U-B= +0.23, R-I= +0.22
Mass: 1.1 x Sol
Diameter: 1.227 x Sol
Source for diameter: European Southern Observatory
Comfort Zone (visual): 1.252 A.U.s
Orbital period in CZ: 1.33536 years
Tidal index in CZ: 0.560791
Angular size of star in sky in CZ: 0.522555 degrees

Component B:
Catalog numbers:
Henry Draper (HD) 128621, Luyten Half-Second (LHS) 51, Hoffleit Bright Star (HR) 5460, Hipparcos Input Catalog (HIC) 71681
Proper motion: 3.689 arcsec/yr (281.1° from north)
Radial Velocity: -18.1 km/sec
Source for proper motion and radial velocity: Gliese
Galactic (U,V,W) velocity components in km/s: -26.17, -1.452, 14.00
Spectral class: K4
Luminosity Class: V
Apparent visual magnitude: +1.34
Absolute visual magnitude: +5.69
Visual luminosity: 0.460 x Sol
Color indices: B-V= +0.84, U-B= +0.64, R-I= +0.29
Mass: 0.85 x Sol
Diameter: 0.869 x Sol
Source for diameter: Lionel
Comfort Zone (visual): 0.678 A.U.s
Orbital period in CZ: 221.389 days
Tidal index in CZ: 2.72186
Angular size of star in sky in CZ: 0.682783 degrees

Component Proxima:
Proper names: Proxima Centauri, V645 Centauri, Alpha Centauri Proxima, Alpha Proxima
Catalog numbers:
Gliese (Gl) 551, Luyten Half-Second (LHS) 49, Hipparcos Input Catalog (HIC) 70890
Right Ascension and Declination: 14h29m42.91s, -62°40'47.2" (epoch 2000.0)
Distance from Sol: 4.223 light-years (1.295 parsecs)
Standard error in distance: 0.31236%
Source for distance: Hipparcos
Celestial (X,Y,Z) coordinates in ly: -1.539, -1.178, -3.752
Galactic (X,Y,Z) coordinates in ly: 2.946, -3.021, -0.169
Proper motion: 3.809 arcsec/yr (281.7° from north)
Radial Velocity: -16 km/sec
Source for proper motion and radial velocity: Gliese
Galactic (U,V,W) velocity components in km/s: -24.68, -2.473, 13.67
Spectral class: M5e
Luminosity Class: V
Apparent visual magnitude: +11.05 (increasing to +10.12)
Absolute visual magnitude: +15.49 (increasing to +14.56)
Visual luminosity: 0.0000555 x Sol (increasing to 0.000131 x Sol)
Variable type: UV Ceti flare star (eruptive variable)
Color indices: B-V= +1.83, U-B= +1.43, R-I= +1.66
Mass: 0.123 x Sol
Source for mass: European Southern Observatory
Diameter: 0.145 x Sol
Source for diameter: European Southern Observatory
Comfort Zone (visual): 0.00745 A.U.s
Orbital period in CZ: 16.0689 hours
Tidal index in CZ: 297597
Angular size of star in sky in CZ: 10.397477 degrees

Data for this star system were most recently updated on 28-July-2004.