Contribution of close double white dwarfs to the Galactic gravitational wave foreground

This paper provides new detailed specifics and characteristics of the close double white dwarfs (CDWDs) LISA foreground noise floor using the newest information on the astrophysics with binary population algorithms, which were judged to satisfy the observations. We use the binary population synthesis approach of CDWDs in combination with the latest findings of synthesis models from Han (Mon. Not. R. Astron. Soc. 296:1019, 1998), here, specifically formation by the three evolutionary channels of (a) stable Roche lobe overflow plus common envelope (RLOF + CE), (b) CE plus CE, (c) exposed core plus CE. We collect resulting CDWDs in the frequency range of 10(-8) Hz to 10(-2) Hz and compare strength and number statistics per resolvable frequency bin to derive the properties of the noise floor and the nature of possible outliers that may become individually resolvable. We find resolvable outliers to be solely produced by CE + CE evolution; the other two channels contribute only to the unresolvable foreground noise. Within the CE + CE evolution a detailed look into the chemical buildup of the stars reveals dominantly double helium (He + He) WDs or carbon-oxygen CO + He WDs.