L2 PUP (L2 Puppis). Directly below the triangle of bright stars to
the south of Sirius lies Pi Puppis (of the constellation of Puppis, the Stern of Argo, the Ship), and almost immediately south of Pi
lies curious L2 Pup. The Roman-letter name harkens back to Bayer's
practice of following his Greek letter
names by lower case Roman letters, followed by upper case
Roman. Bayer's maps of Argo are wildly in error, however, because
the stars could not be seen from mid and northern Europe. He had
to rely on other reports, and did not himself name fairly bright L2
(Nicolas de Lacaille getting into the act). The number is used to
separate this class M (M5) giant from more ordinary and unconnected
fifth magnitude (4.88) class A (A0-peculiar) L1 Pup, which lies
immediately to the south and is at least 10 light years away from
L2. L2 Pup is not only one of the brightest variable stars in the
sky, it is one of the brightest pulsating Mira-type variables, and more, one that can be
followed through its whole cycle with the naked eye. Though
actually classed as a "semi-regular" variable (technically an "SRb"
star), such stars (or at least part of the sample) are now thought
to be just low-amplitude Miras. To the eye, L2 varies between
near-second magnitude (as bright as 2.6) to sixth (6.2) over a 141-
day cycle, meaning that sometimes it is a prominent part of its
parent constellation, other times not (indeed, like Mira itself).
At a distance of 200 light years, this red giant star shines at a
luminosity that is somewhere (depending upon the research adopted)
between 1500 and 2400 times that of our Sun,
radiated from a surface with a temperature of 3400 Kelvin. The
problem is that most of the star's light is emitted in the infrared
rather than in the optical where we directly see it. The star --
with a mass between 1 and 3 solar -- is probably in the early
stages of dying with a dead carbon-oxygen core, though other
scenarios (a dead helium core for example) cannot be ruled out.
Typical of such stars, it is losing mass at a rate estimated
between 3 ten-millionths and 5 hundred millionths of a solar mass
per year (which while it seems low, is a million or so times the
loss rate of the solar wind). The mass of dust gas around the star
produces a silicon monoxide "maser," a natural radio version of the
common "laser." The mass loss rate will someday increase, to
reveal the old nuclear burning core, which will die as a small white dwarf. A curiosity is
the low wind velocity of only a few kilometers per second, again
suggesting early stages of Mira-type behavior. L2 Pup has been
classed as a double star with a 10th magnitude companion about a
minute of arc away. Over the past century, however, the two stars
have separated far more than would be expected, showing that the
seeming neighbor is just a line-of-sight coincidence.