Sirius
Proper names: Sirius, The Dog Star, Alpha Canis Majoris, 9 Canis majoris
Catalog numbers:
Gliese (Gl) 244, Bonner Durchmusterung (BD) -16°1591, Henry Draper (HD) 48915, Aitken Double Star (ADS) 5423, Luyten Two-Tenth (LTT) 2638, Luyten Half-Second (LHS) 219, Hoffleit Bright Star (HR) 2491, A.G. Clark (AGC) 1, Smithsonian Astrophysical Observatory (SAO) 151881, Fifth Fundamental Catalogue (FK5) 257, Hipparcos Input Catalog (HIC) 32349
Age: 300 million years
Heavy element abundance: 410% of Sol
Standard error in heavy element abundance: 16%
Source for heavy element abundance: Strobel [Fe/H] Determinations
Arity: binary
Points of interest:
While Sirius A is known for being the brightest star in the sky, Sirius B was the first White Dwarf to be discovered by humankind (that it took almost a century from the discovery of Sirius B to the acceptance of its White Dwarfness notwithstanding). Sirius B's calculated average density is 92 000 times that of the sun; one cubic inch of material at that density would weigh over two tons at the surface of the Earth. Electron-degeneracy theory predicts that below the surface layers, Sirius B has a uniform density and temperature throughout; however, the outer gaseous layers are probably not electron-degenerate, and thus would not be nearly as dense as the two-tons-to-the-cubic-inch figure previously quoted. (For more information about white dwarfs, see the Lightweight Stars.)
Sirius A is a young star. It has to be; class A main sequence stars exhaust the nuclear fuel in their cores within 1000 million years and turn into red giants or Cepheid variables thereafter. Thus, if there are any life-bearing planets orbiting Sirius A, any life on them will be primitive (it took about 1500 million years for the first oxygen-producing life to develop on Earth, and over twice that long for multicellular organisms to arise).
Due to slight perturbations in the orbit of Sirius B, an additional, unseen companion to either Sirius A or Sirius B is suspected.
Right Ascension and Declination: 6h45m8.871s, -16°42'57.99" (epoch 2000.0)
Distance from Sol: 8.601 light-years (2.637 parsecs)
Standard error in distance: 0.4149%
Source for distance: Hipparcos
Celestial (X,Y,Z) coordinates in ly: -1.612, 8.078, -2.474
Galactic (X,Y,Z) coordinates in ly: -5.745, -6.275, -1.262
Proper motion: 1.328 arcsec/yr (204.3° from north)
Radial Velocity: -9.4 km/sec
Source for proper motion and radial velocity: Gliese
Galactic (U,V,W) velocity components in km/s: 15.34, 1.109, -11.29
What do all these fields mean?
Data for A and B's orbit around one other:
Combined absolute visual magnitude: +1.46
Combined visual luminosity: 22.61 x Sol
Period: 50.09 years
Semimajor Axis: 19.78 A.U.s
Eccentricity: 0.592
Periastron distance: 8.069 A.U.s
Apastron distance: 31.49 A.U.s
Year in which periastron occurs: 1994.31
Source for orbit data: W.H. van den Bos
As seen from A:
At periastron, B would appear as magnitude -15.70
At apastron, B would appear as magnitude -12.75
As seen from B:
At periastron, A would appear as magnitude -25.57
At apastron, A would appear as magnitude -22.62
Component A:
Spectral class: A1
Luminosity Class: V
Apparent visual magnitude: -1.43
Absolute visual magnitude: +1.46
Visual luminosity: 22.61 x Sol
Color indices: B-V= +0.00, U-B= -0.04, R-I= -0.11
Mass: 2.35 x Sol
Diameter: 2.03 x Sol
Source for diameter: Apparent Diameters and Absolute Radii of Stars (Fracassini+ 1988)
Comfort Zone (visual): 4.755 A.U.s
Orbital period in CZ: 6.76389 years
Tidal index in CZ: 0.021858
Angular size of star in sky in CZ: 0.227594 degrees
Component B:
Catalog numbers:
Eggen/Greenstein white dwarf (EG) 49
Spectral class: DA2
Luminosity Class: wd
Apparent visual magnitude: +8.44
Absolute visual magnitude: +11.33
Visual luminosity: 0.00255 x Sol
Color indices: B-V= -0.03, U-B= -1.04
Mass: 0.98 x Sol
Diameter: 0.022 x Sol
Source for diameter: Apparent Diameters and Absolute Radii of Stars (Fracassini+ 1988)
Comfort Zone (visual): 0.0505 A.U.s
Orbital period in CZ: 4.18372 days
Tidal index in CZ: 7621.77
Angular size of star in sky in CZ: 0.232372 degrees
Data for this star system were most recently updated on 4-April-2001.