L2 Puppis

L2 Puppis lies immediately south of π Pup, in Puppis, the Stern of the former constellation Argo Navis. The star's name harkens back to Johann Bayer's practice of following Greek letters by lower case Roman letters, then by upper case Roman. Bayer's maps of Argo are wildly in error, however, because the stars could not be seen from Europe. He had to rely on other reports, and did not name the fairly bright L2 Pup himself. The superscript 2 distinguishes L2 Pup from L1 Pup, which appears magnitude 4.88 immediately to the south.

Properties and Variability

L2 Pup a class M5 III giant, with a surface temperature of 3400 K. It is one of the brightest pulsating Mira-type variables in the sky, and can be followed through its whole cycle with the naked eye. L2 Pup varies between magnitude 2.6 and 6.2 over a 141-day cycle, meaning that sometimes it is a prominent part of its constellation, while at others, it is barely visible. With a distance of 200 light years, this red giant has a luminosity between 1500 and 2400 suns. The star has a mass between 1 and 3 suns, and is probably contains a dead carbon-oxygen core.

Typical of such stars, it is losing mass at a rate estimated to be a million times that of the solar wind. A curiosity is the low wind velocity of only a few kilometers per second, again suggesting early stages of Mira-type behavior. The mass of dust and gas around the star produces a silicon monoxide "maser," a natural microwave version of the optical laser. The mass loss will eventually increase to reveal the star's core, which will evolve to a small white dwarf.

Companion

L2 Pup has been classified as a double star, with a 10th magnitude companion about 1' away. Over the past century, however, the two stars have separated far more than would be expected from orbital motion, showing that the neighbor is just a line-of-sight coincidence.

[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]