Sigma Scorpii

Based upon parallax measurements made during the Hipparcos mission, the distance to Sigma Scorpii is roughly 696 light-years (214 parsecs).

[20] The brightest component of the system, Sigma Scorpii Aa, is a double-lined spectroscopic binary, which means that the pair has not been resolved using a telescope.

[4] The primary component of the spectroscopic binary, Sigma Scorpii Aa1, is an evolved giant star with a stellar classification of B1 III.

During each pulsation cycle, the temperature of the star varies by 4000±2000 K.[4] The other member of the core pair, Sigma Scorpii Aa2, is a main sequence star with a classification of B1 V.[4] Orbiting this binary at a separation of half an arcsecond, or at least 120 Astronomical units (AU), four times the Sun–Neptune distance, is the magnitude +5.2 Sigma Scorpii Ab, which has an orbital period of over a hundred years.

Given its position, youth, and space velocity, the Sigma Scorpii system is a likely member of the Gould Belt,[22] and in particular the Upper Scorpius subgroup of the Scorpius–Centaurus association (Sco OB2).

Rho Ophiuchi cloud complex in the infrared: the "red" at bottom right is 22-micron infrared light from Sigma Scorpii being reflected off the surrounding dust ( Sh2-9 ).
A light curve for Sigma Scorpii, plotted from Hipparcos data [ 21 ]