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.