JABBAH (Nu Scorpii). Small packages often contain great things.
Just northeast of Graffias (Beta
Scorpii) lies a mid-fourth magnitude (4.0) star mostly lost to the
brilliance of the stars of Scorpius,
Jabbah, to which Bayer assigned the Greek letter Nu. Applied to
the star in more modern times, it means "the forehead," and looks
almost like an appendage attached to the scorpion's bright three-
star top. The telescope shows it to be a magnificent quadruple
star, all of whose components are bluish class B. It has been
called "the most beautiful quadruple group in the heavens" (Agnes
Clerke). The stars are arranged in two close pairs that are
separated by 41 seconds of arc. The two of the brighter pair are
split by 1.3 seconds, the two of the fainter by about double that,
2.4 seconds, the set reminding us strongly of the famed "Double-
Double in Lyra," Epsilon Lyrae. The
closeness of them has made measurements of the individuals
difficult. The eastern pair is the brighter, and consists of "Nu
Sco A and B." They are both very hot, roughly 22,000 Kelvin, and
are classed together as B2 subgiants (sometimes dwarfs, as they are
almost certainly still fusing their core hydrogen into helium) with
magnitudes of 4.38 and 5.37. Occultation (covering) by the Moon
reveals that the brighter (A) component is ALSO double, separated
(at the time) by 0.0003 seconds, making the system at least
quintuple, the dimmer (called Ab) about two magnitudes fainter than
the brighter Aa (making Ab a cooler class B star). The western
pair, called "Nu Sco C and D," are respectively B8 and B9 dwarfs
with temperatures about 12,000 and 10,600 Kelvin. From their
common distance of 430 light years and a correction of 0.7
magnitudes for dimming by interstellar dust, in order, Aa, B, C,
and D have luminosities of 2900, 1300, 80, and 40 times that of the
Sun, and masses 8, 6.5, 3, and 2.5 solar. The widely separated
pairs are too far apart for orbital motion to be seen, but A-B and
C-D have clearly grown twice as far apart over the past century or
so. No orbital solution has been possible, so at minimum A and B
are separated by 175 Astronomical Units (AU), B-C by 320 AU, and
AB-CD by 5500 AU, the orbital periods respectively at least 600,
2500, and 91,000 years. The orbital characteristics of the Aa-Ab
pair are unknown. From each of the pairs, the other pair would
appear as brilliant points of light separated by 1 or 2 degrees.
The dimmest component (Nu Sco D) somewhat stands out for somewhat
peculiar chemical composition caused by element diffusion and
separation (notably enhanced silicon), a phenomenon not uncommon
among this type of star.