DABIH (Beta Capricorni). Dabih, the Beta star of Capricornus, the "water goat," is among the more
complex of the sky's naked-eye stars. Second brightest in the
constellation (after Deneb Algedi,
the Delta star), it shines to us at mid-third (3.08) magnitude.
Its name, from ancient Arabic lore that has nothing to do with the
classic Greek constellation, refers to both Dabih and Algedi (Alpha Capricorni) as the "lucky
stars" of a mysterious slaughterer, the true meaning quite lost to
history. The star is a bit of a mess, or at least such is our
knowledge of it. First, it is a wide naked-eye (or at least
binocular) double. The pair, separated by over three minutes of
arc (205 seconds), is dominated by third magnitude "Dabih Major,"
the sixth magnitude (6.10) companion referred to as "Dabih Minor"
(or sometimes Beta Minor, or Beta-2, rendering Dabih Major Beta-1).
At a distance of 330 light years, the two are separated by at least
21,000 astronomical units (AU, the distance between Earth and Sun)
and take at least a million years to make a circuit around each
other. (Obviously no orbital motion has ever been seen.) Dabih
Minor, the simpler of the two, is dominated by a class B (B9.5)
giant or subgiant (meaning it is evolved and has stopped, or nearly
stopped, fusing hydrogen in its core) that shines about 40 times
brighter than our Sun. However, lunar
occultations (in which the Moon covers the star) as well as space-
based observations show it is not one star but two, the other much
fainter and probably a cooler class F ordinary dwarf separated from
its host by about 30 astronomical units (AU, the distance between
Earth and Sun). No orbit has been determined. Dabih Minor is
especially well known, as the brighter components is a "mercury-
manganese" star, one with huge proportions of these elements in its
atmosphere (epitomized by stars like Alpheratz, Elnath, and Gienah
Corvi). Recent measures show platinum, gold, mercury, and
bismuth elevated by 100,000 times the levels found in the Sun, the
result of chemical separation caused by a combination of radiation
and gravity acting in a quiet stellar atmosphere. Dabih Major (the
brighter of the wide pair) is more complex, with a composite
spectrum that nobody seems to agree on, probably class K (K0)
bright giant coupled with a class B (B8) secondary. These are
observed with the spectrograph to take 1374 days (3.8 years) to
orbit each other. The cooler evolved star has a mass just short of
4 times that of the Sun, a temperature of 4900 Kelvin, a luminosity
600 solar, and a radius around 35 solar (a true giant). The hotter
star, with around the same mass, orbits at a distance of some 4 AU.
It, however, is also double made of a close pair that takes only
8.7 days to orbit each other at a separation of only a tenth of an
AU (a third Mercury's distance from the Sun). Nothing is known of
the third component. These seem to have been detected by lunar
occultation as well, and other components may exist. At least
quintuple, and likely yet more "multiple," Dabih could well make an
astronomer's lifetime study.