BETA TRI (Beta Trianguli). Ideally, the Alpha star of a
constellation should rule, though for a variety of reasons it
commonly does not. The brightest star in Orion is Rigel, Beta Orionis,
while in Sagittarius, Rukbat (Alpha Sagittarii) is rather far down
the brightness list. Triangulum, the
Triangle, is another case in point, as our star Beta Trianguli,
right at dead-on third magnitude (3.00), well
outshines Mothallah, Alpha Trianguli,
and moreover has no proper name to glorify it. This warm white
class A (A5) star is hardly without interest, however. Originally
classified as a giant, it has more recently been placed into the
subgiant category, meaning that it has (or will soon) give up core
hydrogen fusion and is beginning to make its run to become a true
red giant. From a distance of 124 light years its 8020 Kelvin
surface shines with a luminosity 71 times that of the Sun, rendering the star 4.4 times larger than
the solar diameter. The luminosity and temperature tell of a star
2.5 times the mass of the Sun that -- as indicated by its
classification -- is indeed just giving up its hydrogen-fusing
dwarf status and is just 580 million years old. Of more interest,
Beta Tri is double. A sunlike companion orbits every 31.8 days at
a distance of 0.3 Astronomical Units, about three-fourths Mercury's
distance from the Sun. A rather large orbital eccentricity takes
the secondary star as far away as 0.42 AU and as close as 0.17 AU.
Beta Tri is also a "Vega"-type star that is
enclosed in a large shell, or more likely a disk, of cool dust that
radiates strongly in the infrared. Such dust-disks suggest
planets. If such exist -- and there is no evidence at all -- they
would have to orbit well outside the companion's orbit, providing
any residents with a spectacular double sunset. Alas, when the
primary star's evolution really gets underway and it expands to
become a giant, its outer envelope will approach if not engulf the
solar companion, causing the two to exchange mass (the matter
flowing from the primary to the companion) and to draw closer
together, paving the way even for a possible future merger.