NU PUP (Nu Puppis). There are so many bright and beautiful stars within the three parts of Argo (Puppis, Vela, and Carina) that the ones that would make a hit in lesser constellations hardly stand out at all. Mid-third magnitude (3.17) Nu Puppis (of no proper name) recommends itself by being the western-most within the classical outline of its constellation, by being in an interesting and fast stage of evolution, and by falling into an arcane and rather weird sub-class. At a distance of 423 light years, this class B (B8) giant, with a measured temperature of 12,000 Kelvin, shines with a luminosity (after allowance for ultraviolet radiation) of 1340 times that of the Sun, which yields a radius 8.5 times solar. Like many of its class, the star is a fast rotator, spinning with an equatorial speed of at least 246 kilometers per second, which gives a rotation period under 1.7 days. The theory of stellar structure and evolution then tell of a hefty five solar mass star that started at class B2. Now around 95 million years old, it gave up its core hydrogen fusion only a few hundred thousand years ago (if that). It is now expanding and cooling at its surface in preparation for brightening as a true red giant only a few million years hence, when it will become many times more luminous. There is some evidence for variability of a couple hundredths of a magnitude over a period of 6.5 days, which would make it an extreme form of "slowly pulsating B star" (like 53 Persei), though it has not actually been so classified. Many fast rotators are "B-emission" (or "Be") stars with circumstellar disks that are related to the spin: Gamma Cassiopeiae and Zeta Tauri come to mind along with many others. While no classic emission has ever been seen, Nu Pup is still called as a "shell star" (with its disk seen edge-on) of a special sort. For all the collectors of arcana, it is one of six "central quasi-emission peak" stars (which have their emissions at wavelengths that fall in the middle of the absorptions rather than to the sides, as is normal), if nothing else showing how odd stellar classification can get. It has, however, been observed in that state but once. It may be on its way to becoming a real "Be" star. Or maybe it was once. But then again, maybe not. We really do not know.
Written by Jim Kaler 3/28/08. Return to STARS.