DENEB DULFIM (Epsilon Delphini). As derived from the Arabic "Al
Dhanab al Dulfim," the "tail of Delphinus the Dolphin," Deneb
Dulfim is but one of a rather remarkable number of "Denebs" that
provide the tails of their respective constellations. The best known is first
magnitude Deneb of Cygnus. But then for us to admire are Deneb Algedi (Capricornus), Deneb
Kaitos (Cetus), Denebola (Leo),
Deneb Okab Borealis and Australis (Aquila), Al Dhanab (Grus), as well as a few other variations on
the theme. It's all confusing enough so as to limit the number
used, and in the present case certainly to go by the Greek letter name given by Bayer,
Epsilon Delphini. A hot star, this fourth magnitude (4.03, ranking
fourth in the constellation just ahead of Delta Del) class B6 nominal giant (but see below) shines with
a blue-white light from a surface heated to an uncertain 14,400
Kelvin. Lying at the fringe of the Milky Way
some 430 light years away, Epsilon Del is subject to about a tenth
of a magnitude of dimming by interstellar dust. Allowance for a
lot of ultraviolet light as a result of its high temperature gives
a total luminosity of 745 times that of the Sun, which in turn leads to a radius of 4.4
times solar, not much for a giant star. Indeed, the theory of
stellar structure and evolution show the star really to be a 4.8
solar-mass dwarf that is perhaps two-thirds of the way through its
hydrogen-fusing 100-million-year lifetime. A projected equatorial
rotation speed of 50 kilometers per second gives a rotation period
of under 4.4 days. The iron abundance is normal, though other
elemental abundances (notably strontium) are not. Though closely
examined, Epsilon Del appears to be decidedly single, with no
companion to watch it whittle itself down through its eventual
giant-star winds. The result will be a carbon-oxygen white dwarf with roughly 85
percent the mass of the Sun, the star losing 80 percent of itself
back into the dusty gas clouds of interstellar space from which it
came.
Written by Jim Kaler 10/17/08. Return to STARS.