MULIPHEN (Gamma Ophiuchi). Duplication plagues star names. The champion is "Deneb," which means "tail" and which has at least seven prominent variations, beginning with first magnitude Deneb itself, Alpha Cygni, then going through Denebola (Beta Leonis), Deneb Kaitos (Beta Ceti), to those quite obscure. The Bright Star Catalogue lists up to 21 of them! Muliphen, not so bad, has three variations, but with a difference, as they are subtly distinguished by their spellings. Oddly, all three are "gammas": Muliphein is Gamma Canis Majoris, Muhlifain is Gamma Centauri, while our star here, Muliphen is Gamma Ophiuchi, a fourth magnitude (3.75) white class A (A0) dwarf at the northeast corner of Ophiuchus's classical figure and just to the west of the prominent asterism called "Poniatowski's Bull." The mangled name (from Kunitzsch and Smart) refers to a conflict between "two things," to two other names for Delta Canis Majoris, and it was apparently applied in error to both Gamma CMa and Gamma Cen. The application to Gamma Oph is so obscure that Allen, in his great book of star names, could not trace it. Though of common spectral class, Gamma Oph is actually quite the interesting star, similar to Vega, but much farther (103 light years) away. The temperature is problematic, estimates from 8500 to 9400 Kelvin averaging 8930 K. It's even more compromised by a very fast projected rotation speed of 200 kilometers per second, which would make the star seriously oblate, which in turn causes the temperature to be higher at the poles, lower at the equator. Allowing for about 20 percent dimming by interstellar dust, the star radiates with the light of 31 Suns, which then gives a qualified radius of 2.3 times solar. The mass then comes in at 2.25 times that of the Sun, theory showing the star to be about half way through its 850 million-year dwarf lifetime. Gamma Oph is surrounded by an infrared-radiating debris disk that powerfully suggests a planetary system, though no actual planets have been detected. Such disks are not uncommon among the stars of class A, those possessing them called "Vega-like." But Gamma Oph's is huge, measured as large as 520 Astronomical Units in radius, some 10 times the size of the Solar System's outer disk, the "Kuiper Belt," which contains countless cometary bodies -- as well as Pluto. Direct measure of stellar radius through interferometry gives a radius twice as large as that derived from luminosity and temperature, probably as a result of confusion by the disk. If the disk's tilt of 50 degrees to the plane of the sky is shared by the star's rotational plane, then it is spinning at 260 kilometers per second, which gives it a rotation period of just under half a day. The metal content, at least, seems rather normal and similar to that of the Sun. If nothing else, the star is a wonderful candidate for planetary searches.
Written by Jim Kaler 8/28/09. Return to STARS.