FURUD (Zeta Canis Majoris). The proper name of this prominent near-dead-on-third-magnitude (3.02) star derives from the Arabic "al-furud," meaning "single" or "solitary ones," a plural applying to any such star, but erroneously stuck on Bayer's Zeta CMa alone. It certainly qualifies, as it is set rather well away from the main figure of Canis Major, to the west and more or less in between the Greater Dog's bottom triangle (with bright Adhara) and the modern constellation Columba, the Dove (making Furud quite easy to find). And as a luminous, hot, blue class B (B2.5) dwarf, it's well worth locating. The star's rather goodly distance of 335 light years (known to an accuracy of about six percent) and proximity to the Milky Way causes it to be dimmed a bit by interstellar dust, by 0.16 magnitudes (about 16 percent). Making that correction, and another for a large amount of ultraviolet light radiated by a surface heated to 21,500 Kelvin, we find a high luminosity 4020 times that of the Sun, which in turn leads to a radius of 4.6 times solar. A minimum equatorial rotation velocity of just 25 kilometers per second (low for the class, suggesting that the star may appear more or less pole-on) gives a rotation period of under 9 days. Stellar structure theory leads to a mass very close to 8 times that of the Sun, and shows the star to be roughly half way through its hydrogen-fusing dwarf lifetime of only 32 million years. While there is a rumor that the star is variable, there seems to be no supporting evidence. In spite of its name, Furud is not solitary, but has a lower-mass "spectroscopic" companion that shifts Furud proper back and forth as the two orbit over a period of 675 days (1.85 years). Nothing is known about it. A guess of two solar masses (consistent with the degree of shift) gives a separation of 3.2 Astronomical Units (60 percent Jupiter's distance from the Sun), a high eccentricity of 0.57 moving the stars between 5.1 and 1.4 AU apart. Furud is listed as having an eighth magnitude companion at an angular separation of nearly three minutes of arc, but the dimmer star's class and motion clearly show the "companionship" to be merely a line-of-sight coincidence. Furud is perilously close to the mass limit above which stars explode as supernovae, but odds are it will someday make a " planetary nebula" and then a massive white dwarf instead, perhaps a rare one composed of neon and oxygen rather than the usual carbon-oxygen mix (the result of advanced nuclear processing). Zeta CMa is an excellent marker for the "Antapex of the Sun's Way," the direction from which the Sun appears to be coming, which lies 3.5 degrees due west of the star in the constellation Columba. The Apex is in Hercules southwest of Vega. (Thanks to Marco Trevisan for comments.)
Written by Jim Kaler 2/02/07. Return to STARS.