DENEBOLA (Beta Leonis). Great Leo, who seems to rule northern spring skies, contains three stars of major note: bright Regulus, second magnitude Algieba (which shares the "Sickle" with Regulus), and mid-second magnitude (2.14) Denebola, the 62nd brightest star in the sky. Denebola, Leo's Beta star (though marginally third brightest after binary Algieba), is the easternmost of a prominent triangle of stars set to the east of Regulus. It provides us with the Lion's tail, the name coming from the Arabic phrase, "dhanab al-asad," which means exactly that. Denebola, a white class A (A3) hydrogen-fusing dwarf star with a temperature of 8750 degrees, shines to us from a relatively nearby distance of 35.9 light years, give or take a mere 0.2 ly (second Hipparcos reduction). Like all the brighter naked eye stars, Denebola is more luminous than the Sun, emitting 13.8 times the solar energy, from which we find a radius of 1.62 times solar. Direct interferometric measure of angular diameter combined with the distance gives 1.65 solar radii, which is consistent with the temperature (no surprise since the temperature was derived from the angular size). A rather rapid projected equatorial rotation speed of 125 kilometers per second yields a rotation period under 0.65 days, the speed enough to prevent chemical peculiarities (by separation in a quiet atmosphere), the iron content also close to the solar value. Denebola is a prominent member of the fairly common "Vega" class of stars that are surrounded by disks of infrared-emitting dust. Since the planets of our Solar System were apparently created from such a circumstellar dusty cloud, Denebola's dust implies the possibility that the star might have planets as well, though there is no direct evidence for them. But direct infrared observation of the dust cloud (N. D. Stock et al., Astrophysical Journal, vol. 724, p. 1238, 2010) reveals a "complex structure" with a hole in the middle an Astronomical Unit in radius, a "dusty ring" 2 to 3 AU in radius heated to about 600 Kelvin, and a 120-Kelvin "broad dusty emission zone extending from about 5 AU to 55 AU." A commonly-seen "dominant outer belt near 100 AU" is missing, the meaning of its lack unknown. Denebola is listed as a subtle variable star of the "Delta Scuti" type. Such stars vary in brightness by small amounts over periods of only hours. However, detailed observations show that it is a spurious designation, the star not varying significantly at all. Three faint "companions" (16th magnitude "B" 40 seconds of arc away from an observation in 1898), 13th magnitude "C" 99 seconds distant, and 9th magnitude "D" some minutes off, all seem to be line-of-sight coincidences. "B" is problematic. It seems to have "disappeared" and may be spurious or might even have been recovered as "C." (Thanks to Bill Hartkopf and Brian Mason.)
Written by Jim Kaler 4/24/98; revised 12/16/11. Return to STARS.