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.