NU OPH (Nu Ophiuchi). There are several oddities (perhaps better said, several points of interest) about this modestly bright third magnitude (3.34) star in southeastern Ophiuchus (the Serpent Bearer). First, practically on the border with Serpens Cauda (the eastern portion of divided Serpens), because of jogs in constellation boundaries, the star lies right on the ragged line that makes the outline of the celestial Serpent. But no, it is really within the confines of Ophiuchus. Second, while sometimes called "Sinistra" (meaning "on the left side"), the proper name does not appear in any classical listings. It probably derives from Chinese lore and seems more astrological in nature, so we stick here with the good old Greek letter name of Nu Oph. Third, while listed as belonging to the Scorpius-Centaurus association of massive stars, it doesn't. Fourth, the star has been said to have a seventh magnitude binary companion a couple seconds of arc away. But Nu Oph is not listed as double in either Burnham's exhaustive "Celestial Handbook" nor in the authoritative Washington Double Star Catalogue, so it is clearly "single" (though with wonderfully important exceptions as told below). Lying 151 light years away (give or take two), Nu Oph then at first appears as just one more class K (K0 at that) giant. But even here there are points of interest. With a temperature of 4825 Kelvin and shining with the radiance of 107 Suns, theory shows Nu Oph to be fairly massive, carrying the "weight" of three Suns (and no less than 2.7), the 400-million-year-old star beginning life as a class B8 dwarf now fusing its internal helium into carbon and oxygen. While a "CN-weak" star (with a lower-than-normal cyanogen abundance, implying low nitrogen or carbon), it is actually metal-rich, with an iron content (relative to hydrogen) a third greater than found in the Sun. A radius of 14 times solar coupled with a projected equatorial rotation speed of 3 kilometers per second yield a rotation period that could be as long as 234 days. There is also a suggestion of far infrared variability. Now to the "exceptions." As the final "oddity," while "single," Nu Oph is attended by a pair of tiny bodies that could at first be thought of as "planets." But they are too massive, and are both really "brown dwarfs," failed stars that are below the 0.075 solar mass limit required to run full fusion, yet are above the 13 Jupiter-mass limit that allows fusion of deuterium (a heavy form of hydrogen). From the Extrasolar Planets Encyclopedia, Nu Oph b, discovered in 2004, carries a mass of at least 22 Jupiters in a 536-day (1.47 year) orbit that averages 1.8 Astronomical Units from Nu proper. Much farther out, at 5.9 AU in an 8.7-year orbit, is Nu Oph c. Found in 2010, it holds at least 25 times the mass of our largest planet (the two respectively having masses of 0.021 and 0.029 solar masses). While called "brown dwarfs" are they really supermassive planets that formed from dust and gas accumulation in an early disk around just-born star, or are they true "stellar" companions that were formed by direct condensation from interstellar matter (as was the star)? And therein lies a specific case of one of the great mysteries of modern astronomy. Not bad for an "ordinary" class K giant (once again showing that at some level, all stars are unique). (Thanks to Paolo Colona, who suggested this star.)
Written by Jim Kaler 8/12/11. Return to STARS.