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| Procyon |
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| Procyon A is a yellowish star that is brighter than our Sun, Sol. (See a Digitized Sky Survey image of Procyon from NASA's NStars Database.) |
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| The Procyon System is located about 11.4 light-years (ly) from our Sun, Sol. Procyon A, or Alpha Canis Minoris A, is the brightest and most centrally located naked-eye star (07:39:18.12+05:13:29.98, ICRS 2000.0) of Constellation Canis Minor (the Smaller Dog). Procyon is also the upper left member of the "Winter Triangle" of first magnitude stars, whose other components are Sirius (Alpha Canis Minoris) at lower left and Betegeuse |
| Alpha Canis Minoris A has a close companion star B that is separated "on average" by only about 16 times the distance from the Earth to the Sun -- 14.9 astronomical units (AUs) of an orbital semi-major axis -- which is roughly the distance between Uranus and our Sun. Alpha Minoris B, the companion star, is a white dwarf, stellar remnant and is so dim that it cannot be perceived with the naked eye. After analyzing irregularities in the proper motion of Procyon which were first detected in 1840, Arthur Julius Georg Friedrich von Auswers (1838-1915) deduced the presence of this faint but massive companion and published a computed period of 40 years in 1861. However, Procyon B was not detected visually until 1896 by John M. Schaeberle (1853-1924) with the 36-inch refractor at Lick Observatory. There is a third optical companion C. |
| Procyon A Alpha Canis Minoris A, the Little Dog Star, is the eighth brightest star in the night sky as well as the brightest star in its constellation. Unlike Sol, it is a white-yellow main sequence dwarf star of spectral and luminosity type F5 V-IV . This relatively large star has about 1.5 times Sol's mass (Girard et al, 2000) and about 1.4 to 2.3 times its diameter (0.00510 to 0.00550", according to the Yale Bright Star Catalogue, 1991 5th Revised Edition notes entry for HR 2943). Compared to Sol, moreover, Procyon A is hotter and about 7.5 times brighter. Procyon radiates somewhat more in ultraviolet wavelengths than Sol, and, not surprisingly, the European Space Agency has used ultraviolet spectral flux distribution data to determine stellar effective temperatures and surface gravities, including those of Procyon. Procyon is probably a relatively young star, but being so much bigger and hotter Sol, the star will exhaust its core hydrogen within even the 4.6 billion years of Sol's current age and turn into a red giant before puffing away its outer layers to reveal a remnant core as a white dwarf. Indeed, Procyon A is unusually bright for its spectral type and so may be becoming a subgiant star that is beginning to evolve off the main sequence, as it begins to fuse the increasing amounts of helium "ash" mixed with hydrogen at its core. The star is rich in elements heavier than hydrogen ("metals rich"), as it has about 1.4 times the iron abundance of Sol, and dust has been detected in the system (Kuchner and Brown, 2000 -- in postscript). It was probably enriched by its companion star, which was once bigger and hotter than Procyon A and so evolved and "burnt out" even faster. Procyon B manufactured lots of heavier elements which it puffed out into space and onto Procyon A before becoming a white dwarf. Procyon A is a BY Draconis-type variable star. Not only can its companion boost its brightness when located in front of the star as observed from Earth, but its intrinsic brightness actually varies as well. In addition to its New Suspect Variable (NVS) designation of NVS 3672, some other useful names and star catalogue numbers include: Alp or Alf CMi, 10 CMi, HR 2943, Gl 280 A, Hip 37279, HD 61421, BD+05 1739, SAO 115756, FK5 291, LHS 233, and ADS 6251 A. Previous estimates of the orbital elements of this binary system calculated by Irwin et al in 1992 and by Kaj Aage Gunnar Strand (1907-2000; obit) in 1951 have been superceded. Based on new measurements (Girard et al, 2000) found in the new Sixth Catalog of Visual Orbits of Binary Stars, Procyon A and B may be separated on average by a semi-major axis of 14.9 AUs (4.271") in an elliptical orbit |
| (e= 0.407) that takes 40.82 years to complete. The distance separating the two stars varies from 8.9 and 21.0 AUs; they are always separated from each other by roughly the orbital distance of Saturn in the Solar System. Lastly, the inclination of the orbit is 31.1°, from the perspective of an observer on Earth. (See an animation of the orbits of Stars A and B and their potentially habitable zones, with a table of basic orbital and physical characteristics.) Procyon B This much dimmer star is a white dwarf (DA-F or A-F VII), whose close proximity and large disparity in brightness with its primary have made precise determination of its luminosity, colors, and spectrum difficult (Irwin et al, 1992). At least 15,000 times fainter than Procyon A, it is also only 6/10,000th as luminous as Sol. Procyon B appears to have 60 percent of Sol's mass (Girard et al, 2000) but only about two percent of its diameter. In fact, its diameter may be no more than about 17,000 km (about 10,500 miles), which is only about 30 percent more than Earth's. On the other hand, white dwarfs are incredibly dense objects because they squeeze a stellar mass into a planetary volume, and so Procyon B's average density is estimated to be over two tons to the cubic inch. While tiny compared to main sequence stars, white dwarf stars are actually intensely hot, but without the internal heat of fusion to keep them burning, they gradually cool, redden, and fade away. As some star catalogues note that Star B actually appears yellowish, it is likely that this "white" dwarf is been cooling for a very long time and is much older than Sirius B. Useful star catalogue numbers for this Procyon B include Gl 280 B and ADS 6251 B. |
| Luyten's Star M3.5-5 Ve 1.2 Ross 614 AB M4.5 Ve ? 4.6 DX Cancri M6.5 Ve 5.0 Sirius 2 A0-1 Vm DA2.5/VII 5.2 LTT 12352 M3.5 V 5.3 GJ 1116 AB M5.5 V M5.5 V 8.0 Ross 882 AB M4 Ve M5 Ve 8.0 Wolf 359 M5.8 Ve 8.6 LTT 17993 M4.5 V 8.7 LTT 17897 M4 V 8.8 Lalande 21185 M2.1 Ve 9.6 Wolf 294 M3 V 9.9 |