ALADFAR (Eta Lyrae). Lyra, the Lyre or Harp, is so dominated by the set of six stars that make the exquisite figure that we barely pay attention to any of the others in the constellation. Oddly, while only three of the inner six (Vega, Sheliak, and Sulafat, respectively Alpha, Beta, and Gamma) have proper names, so does one of the outliers, fourth magnitude (4.39) Eta Lyrae, which is erroneously called Aladfar (the "talons" of an eagle), the name apparently stolen from another outlier, Mu Lyrae (Al Athfar). Aladfar is a hot, blue-white class B (B2.5) subgiant that has either quit core hydrogen fusion or will do so shortly and that is beginning its rapid (at least on an astronomical time scale) evolution toward becoming a red giant. The temperature is uncertain, having been first measured at 17,950 Kelvin and later presumably better-determined at 16,045. The latter, however, is more like that of a class B4 star, whereas the hotter value is more appropriate, and will be adopted here. Allowance for the star's ultraviolet light yields a luminosity 6500 times that of the Sun, a radius of 8.4 solar, and a mass of 7.5 solar or 8 solar depending on the exact state of evolution, the age around 30 million years. Unlike many class B stars, Aladfar rotates slowly, the equatorial velocity greater than or equal to just 10 kilometers per second, giving a rotation period of 42 days or under. Slow class A or B rotators frequently have weird chemical compositions that are the result of diffusion of elements in quiet stellar atmospheres. That Aladfar is not chemically odd suggests that the rotation velocity is really much higher and that the star's rotation axis is more or less pointing at us. About half a minute of arc away lies a class A0 "companion" that is merely a line of sight coincidence. Aladfar's spectrum, however, reveals the possibility of a real close-in companion that orbits with a period of 56.4 days, but about which nothing is known. If the companion is like the Sun, it is some 0.6 Astronomical Units from Aladfar proper. Aladfar appears to be just under the limit at which stars explode as supernovae, and after ejecting most of itself back into space through powerful winds will most likely end its regular life as a massive white dwarf not far from the 1.4 solar mass limit allowed for such stars. However, it might still provide a spectacular event. If the star's evolution encroaches on the companion, it might bring the little one close enough to dump mass on the developing white dwarf so as to overflow the 1.4 limit, the result again a spectacular supernova.
Written by Jim Kaler. Return to STARS.