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Sirius is a binary star system consisting of two white stars orbiting each other with a separation of about 20 AU[60] (roughly the distance between the Sun and Uranus) and a period of just over 50 years. The brighter component, termed Sirius A, is a main sequence star of spectral type A0 or A1, while its companion, Sirius B, is a star that has already evolved off the main sequence and become a white dwarf. Currently 10,000 times less luminous in the visual spectrum, Sirius B was once the more massive of the two. The age of the system has been estimated at around 230 million years. Early in its lifespan it was thought to have been two bluish white stars orbiting each other in an elliptical orbit every 9.1 years.[61] The system emits a higher than expected level of infrared radiation, as measured by IRAS space-based observatory. This may be an indication of dust in the system, and is considered somewhat unusual for a binary star.[62][59]
http://en.wikipedia.org/wiki/Sirius#System
The spectrum of Sirius A shows deep metallic lines, indicating an enhancement in elements heavier than helium, such as iron.[10][59] The proportion of iron in the atmosphere of Sirius A is given by ,[7] which is equivalent to 100.5, or about 316% of the proportion of iron in the Sun's atmosphere. The high surface content of metallic elements is unlikely to be true of the entire star. Instead these may be suspended by a thin convection zone at the surface.[10]
http://en.wikipedia.org/wiki/Sirius#Sirius_A
This star is primarily composed of a carbon-oxygen mixture that was generated by helium fusion in the progenitor star.[8] This is overlaid by an envelope of lighter elements, with the materials segregated by mass because of the high surface gravity.[68] Hence the outer atmosphere of Sirius B is now almost pure hydrogen—the element with the lowest mass—and no other elements are seen in this star's spectrum.[69]
http://en.wikipedia.org/wiki/Sirius#Sirius_B
http://en.wikipedia.org/wiki/Sirius#...l_significance
http://en.wikipedia.org/wiki/Sirius_in_fiction
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