KAUS MEDIA (Delta Sagittarii). Sagittarius is known more for its two "asterisms" (informal constellations), the "Little Milk Dipper" and the "Teapot," than it is for the figure it was meant to represent, a Centaur Archer. And what is an archer without a bow? Sagittarius has a fine one, not just a bow, but an arrow along with it that points into the heart of the Milky Way. At the bow's northern end lies Kaus Borealis, at the southern Kaus Australis, and in the middle and marking the eastern end of the arrow Kaus Media, the names an odd mixture of languages, Kaus coming from an Arabic word meaning "bow," while the other three words respectively mean, from Latin, "northern," "southern," and "middle." At the bright end of third magnitude (2.70), Kaus Media ranks second brightest in the bow (after Kaus Australis) and fourth in the constellation (fitting for Bayer's Delta star), behind Sigma (Nunki), Epsilon (Kaus Australis), and Zeta ( Ascella); it's hard to know what Bayer had in mind! Kaus Media is yet one more class K (K3) giant star, but one a bit on the bright side. Its distance of 305 light years and an uncertain temperature of 4300 Kelvin (needed to account for infrared radiation) lead to a luminosity 1180 times that of the Sun and a radius 62 times solar, the star three-quarters the size of Mercury's orbit. Oddly, the temperature has never actually been measured, and can only be inferred from the K3 spectral class. The amount of dimming by interstellar dust is also uncertain, and while it cannot be much, the star may actually be up to 30 percent brighter and 15 percent larger. With a relatively high mass 5 times that of the Sun, Kaus Media is mostly likely fusing helium into carbon in its core. The star is an example of how little we can know about companions, especially within the rich star fields of the Milky Way. Catalogues list three faint neighbors, 14th, 15th, and 13th magnitude stars at separations of 26, 40, and 58 seconds of arc. If these are true companions, they are class K and M dwarfs, are at real distances of at least 2400 to 5400 Astronomical Units (Earth-Sun distances) from Kaus Media proper, and take at least from 53,000 to 180,000 years to orbit. The little stars might also be line of sight coincidences. Spectra display some evidence for a possible close companion as well, which might be related to the star's uncertain reputation as a weak "barium star," one that has been contaminated with heavy elements by an evolving orbiting neighbor. Clearly the star needs more attention than it gets.
Written by Jim Kaler. Return to STARS.