109 VIR (109 Virginis). Bright fourth magnitude (3.73), part of the outline of the constellation Virgo, we might still tend to roll over 109 Virginis (best known by its Flamsteed number) as just another white class A hydrogen-fusing dwarf (A0 at that, same as Vega), its distance 134.5 light years, accurate to a mere one light year. Just two degrees north of the celestial equator and the second-most-easterly numbered star in Virgo, the star is beaten (as expected) only by 110 Vir, a dimmer (magnitude 4.40) ordinary class K (K0.5) orange giant 195 light years away. We tend to disparage such stars as overly common, but without them many of the constellation figures would dissolve; cut out the class B dwarfs too and there would not be much left at all. 109 Vir is also notable as an old photometric standard, one used to calibrate the spectral brightness of other stars. But there is much more. With a temperature of 9760 Kelvin, which tells of a bit of ultraviolet radiation, the star shines with a luminosity of 52 times that of the Sun, from which we derive a radius of 2.5 times solar and a mass of 2.5 Suns. With an age of 360 million years, it's just over 60 percent of the way through its 585 million year hydrogen fusing lifetime. The star stands out for its rapid equatorial rotation of at least 325 kilometers per second, which gives it a rotation period of under 9.3 hours. The fast rotation somewhat compromises the temperature, as it flattens the star, which makes it hotter at the poles, cooler at the equator. Some have thought it to be a metallic-line star, in which the metallic spectral absorption lines are enhanced, as seen in Zeta Lyrae, Subra (Omicron Leonis), Sirius, and so many other class A stars. But it's hard to see how that could be true given the high rotation velocity, which stirs up the atmosphere, so it's an unlikely possibility. There is also a claim of metal deficiency, the iron content 40 percent that of the Sun. There appears to be no significant debris disk left over from 109's birth like those surround Vega or Fomalhaut and that would suggest planets. However the star may have a real companion. Nineteenth and twentieth magnitude 109 Vir D and C are respectively 9.3 and 5.7 seconds from bright "A." But they have been observed only once, so there is no way of knowing if they track along with the main star. They are most likely line of sight coincidences. But then there is 109 Vir B. At magnitude 9.7 it's seen just 0.6 seconds from "A," which would give it a minimum separation of 25 Astronomical Units. From the star's true brightness it would be a K4 dwarf with a mass of around 0.7 times that of the Sun. From Kepler's laws, the orbital period would be least 69 years. Confirmation awaits.

Written byJim Kaler 5/02/14. Return to STARS.