Draco Dwarf

Paul W. Hodge analyzed the distribution of its stars in 1964 and concluded that its ellipticity was 0.29 ± 0.04. Recent studies have indicated that the galaxy may potentially hold large amounts of dark matter. Having an absolute magnitude of −8.6 and a total luminosity of only , it is one of the faintest companions to our Milky Way. Draco Dwarf contains many red giant branch (RGB) stars; five carbon stars have been identified in Draco Dwarf and four likely asymptotic giant branch (AGB) stars have been detected. From this work a RR Lyrae derived distance modulus of 19.55 is found which implies a distance of 81 kpc. The modern estimate is 80 ± 10 kpc from Earth and its size is around 830 ± 100 × 570 ± 70 pc. ==Metallicity==

The Draco Dwarf contains primarily an old population of stars and insignificant amounts of interstellar matter (being basically dust free). It has a single Gaussian distribution with average metallicity of [Fe/H] = −1.74 dex with a standard deviation (sigma/σ) of 0.24 dex and a small tail of metal-rich stars. The central region of Draco Dwarf exhibits a concentration of more metal-rich stars there being more centrally concentrated red horizontal branch stars than blue horizontal branch stars. ==Dark matter==

Recently, dwarf spheroidal galaxies have become key objects for the study of dark matter. The Draco Dwarf is one which has received specific attention. Radial velocity measurements of individual stars in Draco have revealed a large internal velocity dispersion giving a mass to luminosity ratio of up to /, suggesting large amounts of dark matter. It has been hypothesized that large velocity dispersions could be explained as tidal dwarfs (virtually unbound stellar streams from dwarf galaxies tidally disrupted in the Milky Way potential). However, Draco Dwarf's narrow horizontal branch width does not support this model. This only leaves the dark matter explanation and makes Draco Dwarf the most dark matter dominated object known as of 2007. ==Notes==