Star last to depart Sin City (4)

I believe the answer is:

vega

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'star' is the definition.
(star in the constellation Lyra)

I don't understand how the rest of the clue works.

(Other definitions for vega that I've seen before include "Bright star of constellation Lyra" , "Fifth brightest star" , "First magnitude star" , "heavenly body" , "Gave turn to a star" .)

I've seen this clue in The Times.

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