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DENEBOLA (Beta Leonis). GreatLeo, whoseems to rule northern spring skies, contains three stars of majornote: brightRegulus, second magnitudeAlgieba (which shares the "Sickle" with Regulus), and mid-second magnitude (2.14)Denebola, the 62nd brightest star in the sky. Denebola, Leo's Betastar (though marginally third brightest afterbinary Algieba), is theeasternmost of a prominent triangle of stars set to the east ofRegulus. It provides us with the Lion's tail, the name coming fromthe Arabic phrase, "dhanab al-asad," which means exactly that. Denebola, a white class A (A3) hydrogen-fusing dwarf star with atemperature of 8750 degrees, shines to us from a relatively nearbydistance of 35.9 light years, give or take a mere 0.2 ly (secondHipparcos reduction). Like all the brighter naked eye stars,Denebola is more luminous than theSun,emitting 13.8 times the solar energy, from which we find a radiusof 1.62 times solar. Direct interferometric measure of angulardiameter combined with the distance gives 1.65 solar radii, whichis consistent with the temperature (no surprise since thetemperature was derived from the angular size). A rather rapidprojected equatorial rotation speed of 125 kilometers per secondyields a rotation period under 0.65 days, the speed enough toprevent chemical peculiarities (by separation in a quietatmosphere), 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 bydisks ofinfrared-emittingdust. Since the planets of our Solar System were apparentlycreated from such a circumstellar dusty cloud, Denebola's dustimplies the possibility that the star might haveplanets as well, though there is no directevidence for them. But direct infrared observation of the dustcloud (N. D. Stock et al., Astrophysical Journal, vol. 724, p.1238, 2010) reveals a "complex structure" with a hole in the middlean Astronomical Unit in radius, a "dusty ring" 2 to 3 AU in radiusheated to about 600 Kelvin, and a 120-Kelvin "broad dusty emissionzone extending from about 5 AU to 55 AU." A commonly-seen"dominant outer belt near 100 AU" is missing, the meaning of itslack unknown. Denebola is listed as a subtle variable star of the"Delta Scuti" type. Such stars vary inbrightness by small amounts over periods of only hours. However,detailed observations show that it is a spurious designation, thestar not varying significantly at all. Three faint "companions"(16th magnitude "B" 40 seconds of arc away from an observation in1898), 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 spuriousor might even have been recovered as "C." (Thanks to Bill Hartkopfand Brian Mason.) Written byJim Kaler 4/24/98; revised12/16/11. Return toSTARS.
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