NU AUR (Nu Aurigae). Lost to time, the ancients made up the classical constellations. In the seventeenth and eighteenth centuries, astronomers then filled in the blanks. But why stop there? It's rather fun to make up one's own from the scattered patterns in the sky. Capella, the "she-goat" in classical Auriga, gleams brightly from the far northern sky. To the southwest of it is a slim triangle, an asterism (informal constellation) called "The Kids," which originally consisted of Haedus I and II (Zeta and Eta Aurigae), but now by usual agreement also includes Almaaz (Epsilon) at the northern apex. Look then at a photo of the constellation, or at a good star map. By rather remarkable coincidence, to the northwest of Theta Aurigae lies an almost exact replica of The Kids, just reversed and a magnitude fainter. Made of fourth magnitude (3.97) Nu Aurigae and fifth magnitude Tau and Upsilon, it's almost impossible not to call them "The Little Kids."
The Little Kids. North is to the left. Theta Aurigae, near bottom center, leads the eye upward to the thin triangle of stars we might call "The Little Kids," made (clockwise from lower left) of Nu, Tau, and Upsilon Aurigae. The figure is remarkably similar (though reversed) to the classic "Kids" near Capella, made of Epsilon, Zeta, and Eta Aurigae.
By further coincidence, all are giants, the brightest of them, Nu Aur (at the northeastern apex) an orange one of class K (K0). (Auriga seems to attract coincidences: Theta, Beta, Pi, and Delta all line up along the solstitial colure, the circle that connects the solstices and the celestial poles.) Lying at a distance of 66 light years, from a coolish surface of 4550 Kelvin Nu Aur shines with the light of 163 Suns (after a small correction for interstellar dust absorption), which leads to a radius of 21 times that of the Sun and a substantial mass of 3 times solar. Direct measure of angular diameter through interferometry gives a satisfyingly close result of 20 solar radii. Nu Aur is a classic example of a helium- fusing "clump star," the "clump" referring to a great many stable stars with similar temperatures and luminosities. Having begun life as a B8 dwarf 400 million years ago, it gave up hydrogen fusion some 350 million years later. After losing its outer envelope through winds when helium-burning is over, its fate is to become a white dwarf of about 0.7 solar masses. At a separation of 56 seconds of arc lies an 11th magnitude (11.4) companion that at Nu's distance would be a K6 dwarf. A minimum orbital radius of 3700 Astronomical Units leads to a period of at least 120,000 years. While having been called a line-of-sight "optical" pair, the two do seem to be tracking each other, suggesting real binarity. Want one more coincidence? Nu and Tau are at almost the same distance from Earth, the latter just a couple light years closer (at least at the measured distances, which are subject to about five percent uncertainty). Given the angular separation of about 0.4 degrees, the two would then be just 3 light years apart, causing Tau to shine in Nu's sky about as brilliantly as Venus does in ours.
Written by Jim Kaler 3/14/08. Return to STARS.