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.