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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 Ghurab). 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.
ntuple, and likely yet more "multiple," Dabih could well make an astronomer's lifetime study.