Categories: Stars

Star Facts: Procyon

Procyon by F. Espenak [astropixels.com]

Procyon is the most luminous star in the constellation Canis Minor, and the 8th most luminous star in the entire night sky. The star may appear yellowish-white, but Procyon is in fact a binary system comprising a late-stage main sequence star, and a dead white dwarf. It is also one of our closest neighbours at only 11 or so light years away, which means you don’t need optical aids to see it blazing in the sky. You only have to look up to see it, so go out, and look for it tonight!

Procyon means “before the dog” in Greek as it was seen to rise before the Dog Star (Sirius in Canis Major) each night. Due to precession over time, this is now only true from mid-northern latitudes.

Quick Facts

• Constellation: Canis Minor
• Coordinates: RA 07h 39m 18.1/17.7s | Dec +05° 13′ 29/20
• Distance to Earth: 11.46 light years
• Star Type: white main-sequence Procyon A (F5 IV–V), white dwarf Procyon B (DQZ)
• Mass: Procyon A: 1.499 solar mass | Procyon B: 0.602 solar mass
• Radius: Procyon A : 2.048 solar radii | Procyon B : 0.01234 solar radius
• Apparent Magnitude: Procyon A: 0.34 | Procyon B: 10.7
• Luminosity: 6.93 solar luminosity (Procyon A)
• Surface Temperature: Procyon A: 6,530K | Procyon B: 7,740K
• Rotational Velocity: 3.16 km/s (Procyon A)
• Age: Procyon A : 1.87 billion years | Procyon B : 1.37 billion years
• Other Designations: Elgomaisa, Algomeysa, Antecanis, Alpha Canis Minoris

The Winter Triangle

Procyon in Canis Minor, Sirius in Canis Major, and Betelgeuse in Orion together form a collection of 1st magnitude stars known as the Winter Triangle, and are therefore rather hard to miss. Procyon has a colour index of 0.42, giving it a faint yellow tinge, which contrasts sharply with the brilliant white of Sirius, and the red glow of Betelgeuse. Look for the Winter Triangle and particularly Procyon during late winter, when the star culminates at midnight on the 24th of January.

Physical Properties of the Procyon System

Although Procyon appears to be a single star when viewed from Earth, it is in fact a binary system with an orbital period of 40.82 years. The primary star of the system, Procyon A, has an apparent visual magnitude of 0.34, while the companion star, Procyon B, is an almost dead white dwarf with an apparent magnitude of 10.7, which makes it an exceedingly difficult target for amateur equipment. The separation between the orbiting pair varies from 8.9 AU to as much as 21 AU, with an average separation of 15 AU, which is just a little less than the mean distance between the Sun and the planet Uranus.

– Procyon A is a white main sequence star (F5IV–V) about twice as big as the Sun, 1.4 times as massive, but with a significantly higher surface temperature of 6550K (11,300 degrees F), making it 6.9 times more luminous than the Sun. The star is rapidly evolving off the main sequence, with its high luminosity suggesting that it has nearly converted all of its hydrogen into helium, and is thus moving into the sub-giant class. Eventually it will swell up to anything between 80 and 150 times the diameter of the Sun somwhere between 10 million and 100 million years from now.

– Procyon B, is a dead white dwarf that is believed to have died about 1.19 billion years ago, after having spent only about 680 million years on the main sequence. It has a radius of 8,600 km, a mass of only 0.6 our sun, and is assumed to have carbon core.

Proper Motion

Procyon is not noted for its high proper motion, which comes to 4.446 AU/year at a velocity of 21.078 km/sec. The combined motions of the system across the sky means that in 323,140 years’ time, Procyon will become an eclipsing binary system for about 190 years when viewed from Earth, as its orbital plane crosses the Sun-Procyon line. Some time before that though, in 31,490 years’ time to be exact, Procyon will reach its closest point of approach to the Sun, when it will be 11.19 light years (707,574 AU) away, after having crossed 11.19 degrees of the celestial sphere.

Procyon in History

In Greek mythology, Procyon is associated with a hound named Maera, which belonged to Erigone, the daughter of Icarius of Athens. To the Romans, however, the star was known as Antecanis, which roughly means “Not the Dog Star”. In ancient Macedonia, where the constellations mostly represented animals and agricultural implements that reflected the old Macedonian way of life, Procyon and Sirius were known as “Volci”, two hungry wolves circling Orion, which to the Macedonians, represented a plough and oxen, and not the hunter of other cultures. In 16th and early 17th century England, Procyon was referred to in some circles as “Northern Sirius”. The official Brazillian flag adopted in 1889 contains 27 stars, each representing a seperate state, which in the case of  Amazonas is depicted by the star Procyon.

Peter Christoforou :