ALPHA RET (Alpha Reticuli). Though shining at relatively prominent third magnitude (3.35), and the luminary of the modern constellation Reticulum (the Net), Alpha Reticuli is largely ignored by the research community since the great majority of astronomers are in the northern hemisphere where they cannot see it, the star easily visible only from south of the Tropic of Cancer. If in the northern hemisphere, Alpha Ret would be a common star within most statistical data bases (and probably would have had an "ancient" proper name). Lying at a distance of 163 light years, Alpha Ret is a yellow class G (G8) "bright giant," that is, is somewhat on the bright side even for a giant star. Radiating at a luminosity of 237 Suns from its coolish 4940 Kelvin surface, the star has a giant's radius 21 times that of the Sun, and has a rotation period slow enough that it has never been measured (with an upper limit of 130 days). It does, however, radiate X- rays, which shows magnetic activity likely induced by rotation. Alpha Ret's temperature and luminosity together with the theory of stellar structure suggest a mass 3.5 times that of the Sun. A rather standard "clump giant" (a star that quietly fuses its helium into carbon and oxygen), only 300 million years ago it was a luminous blue class B star. Upon burning up the rest of its internal helium, it will undergo a great brightening phase and then pop its external envelope as it prepares to become a white dwarf. Unless it is torn away by the gravity of passing stars, all this action will continue to be witnessed by a small twelfth magnitude class M0 dwarf companion. Over the past 150 years, the little one has kept the same motion as the big one, showing that the two really are mated and not just a line of sight coincidence. (Technically, they are a called a "common proper motion" pair, "proper motion" being the movement of the star against the distant background.) The separation of 49 seconds of arc translates into a minimum physical separation of 2450 Astronomical Units and an orbital period of at least 60,000 years. At this distance, from Alpha Ret proper the companion would glow 4 or so times our Venus at maximum, while from the companion, Alpha Ret would shine with the light of 15 full Moons.
Written by Jim Kaler. Return to STARS.