System
Procyon A has a stellar classification of F5IV–V. The effective surface temperature of the star is an estimated 6,530 K, giving it a white hue. It is 1.4 times the mass, twice the radius, and 6.9 times more luminous than the Sun. Procyon A is bright for its spectral class, suggesting that it is a subgiant that has nearly fused its core hydrogen into helium, after which it will expand as "burning" moves outside the core. As it continues to expand, the star will eventually swell to about 80 to 150 times its current diameter and become a red or orange color. This will probably happen within 10 to 100 million years.
Like Sirius B, Procyon's companion is a white dwarf that was inferred from astrometric data long before it was observed. Its existence had been postulated by Friedrich Bessel as early as 1844, and although its orbital elements had been calculated by Arthur Auwers in 1862 as part of his thesis, Procyon B was not visually confirmed until 1896 when John Martin Schaeberle observed it at the predicted position using the 36-inch refractor at Lick Observatory. It is more difficult to observe from Earth than Sirius B, due to a greater apparent magnitude difference and smaller angular separation from its primary. The average separation of the two components is 15.0 AUs, a little less than the distance between Uranus and the Sun, though the eccentric orbit carries them as close as 8.9 AUs and as far as 21.0 AU.
At 0.6 solar masses, Procyon B is considerably less massive than Sirius B; however, the peculiarities of degenerate matter ensure that it is larger than its more famous neighbor, with an estimated radius of 8,600 km, versus 5,800 km for Sirius B. With a surface temperature of 7,740 K, it is also much cooler than Sirius B; this is a testament to its lesser mass and greater age. The mass of the progenitor star for Procyon B was about 2.5 solar masses and it came to the end of its life some 1.7 ± 0.1 Gyr ago, after a main-sequence lifetime of 400–600 Myr. For this reason, the age of Procyon A is expected to be at least 2 Gyr.
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