TAU PUP (Tau Puppis), which completes STARS' set of the 168 stars
of magnitude 3.00 and brighter. The
glories of the southern ancient constellation Argo, which represents the Ship of the ancient
Argonauts that seemed to float across the "wine-dark sea," are so
legion as to diminish any but the brightest stars. It was divided
long ago into its three sub-divisions of Vela (the Sails), Carina (the
Keel), and Puppis (the Stern). Each holds
its own glories, which include Eta
Carinae (one of the most luminous stars in the Galaxy), Gamma Velorum (which contains the visually
brightest dying "Wolf-Rayet" star), and Canopus (Alpha Carinae), the second
brightest star as seen from Earth, topped only by Sirius, which rides the sky to the north of
it. No one pays much attention to the few stars that gather about
Canopus, which receives all the attention. But a bit to the
northeast of it is something of a marker star that helps define the
boundary between northern Carina and
southern Puppis, easily-visible third
magnitude (2.93, ranking it in the top 160 stars) Tau Puppis, which
lies just barely over the line. Other than that, Tau Pup seems
like just one more among the host of common class K helium-fusing
giants (Tau class K1), without
which however many of our constellation
patterns would effectively disappear. Still, the star comes with
a couple recommendations. Quite neglected, there are no
temperature measures, so we adopt 4600 Kelvin from the spectral class. Not all that far
away, 182 light years (give or take 4), 60 percent Canopus's
distance, it shines with the light (including infrared) of 270 Suns, which leads to a radius of 26.0 times
solar, very close to the value of 26.6 adopted for use in the
calibration of interferometer measures of the diameters of other
stars. Theory then reveals a fairly high mass of 3.3 times that of
the Sun, confirms that indeed Tau Pup is a classic stable helium-
burning giant, provides an age of around 300 million years, and
shows that the star began life as a much warmer, blue-white class
B7 dwarf. Correction for a modest amount of interstellar dust
absorption (which from the data is not clearly required) could at
the very most raise the luminosity by 50 percent and the mass to 4
Suns. Not alone, Tau Puppis is accompanied by a spectroscopically-
detected companion that takes 2.9
years to orbit at a distance estimated at around 3 Astronomical
Units, the distance changing slightly as a result of a 10-percent
eccentricity. From the deflection of Tau proper, it's most
likely to be a red dwarf. Nothing else seems to be known about either of the
pair, which seems to be the fate of living a life in such rich
surroundings.
Written by Jim Kaler 5/20/11. Return to STARS.