- This article is about the star. Procyon is also the mammalian genus to which raccoons belong.
(α CMi / α Canis Minoris / Alpha
Canis Minoris) is the brightest star
in the constellation Canis Minor
. To the naked eye, it appears to be a single star, the eighth brightest
in the night sky with a visual apparent magnitude
of 0.34. It is actually a binary star
system, consisting of a white main sequence
star of spectral type
F5 IV-V, named Procyon A
, and a faint white dwarf
companion of spectral type DA, named Procyon B
. The reason for its brightness is not its intrinsic luminosity but its closeness to the Sun
; at a distance of 3.5 pc
or 11.41 light years
, Procyon is one of our near neighbours
. Its closest neighbour is Luyten's star
, 0.34 pc or 1.11 ly away.
Procyon forms one of the three vertices of the Winter Triangle, along with Sirius and Betelgeuse.
Procyon A is a white star of spectral type F5; it is 1.4 times the mass, twice the diameter, and 7.5 times more luminous
than the Sun
.,,. It is bright for its spectral class, suggesting that it is a subgiant
that has completely fused
its core hydrogen into helium, and begun to 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. It is expected that the Sun will also go through this process when hydrogen fusion ceases at its core.
Like Sirius B, Procyon's companion is a white dwarf that was inferred from astrometric data long before it was observed; though its orbit was known as far back as 1861, it was not visually confirmed until 1896. It is even 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 AUs, a little less than the distance between Uranus and the Sun, though the eccentric orbit carries them as close as 9 AUs and as far as 21.
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 ~8600 km, versus ~5800 km for Sirius B., With a surface temperature of 7740 K, it is also much cooler than Sirius B; this is a testament to its lesser mass and greater age.
In late June 2004, Canada
's orbital MOST satellite telescope
carried out a 32-day survey of Procyon A. The continuous optical monitoring was intended to confirm solar-like oscillations
in its brightness observed from Earth and to permit asteroseismology
. No oscillations were detected and the authors concluded that the theory of stellar oscillations may need to be reconsidered. However others argued that the non-detection was consistent with published ground-based radial velocity
observations of solar-like oscillations
Photometric measurements from the NASA Wide Field Infrared Explorer (WIRE) satellite from 1999 and 2000 showed evidence of granulation (convection near the surface of the star) and solar-like oscillations. Unlike the MOST result, the variation seen in the WIRE photometry was in agreement with radial velocity measurements from the ground.
Etymology and cultural significance
Its name comes from the Greek προκύον
), meaning "before the dog", since it precedes the "Dog Star" Sirius
as it travels across the sky due to Earth
's rotation. (Although Procyon has a greater right ascension
, it also has a more northerly declination
, which means it will rise above the horizon
earlier than Sirius from most northerly latitudes.) These two dog stars
are referred to in the most ancient literature and were venerated by the Babylonians
and the Egyptians
It is known as 南河三 (Nánhésān, the Third Star in the Southern River) in Chinese.