Multiplicity among Solar-type Stars

We present a multiplicity census for a volume-complete all-sky survey of 422 stars with distances less than 25 pc and primary main-sequence effective temperatures T-eff >= 5300. K. Very similar to previous results that have been presented for various subsets of this survey, we confirm the positive correlation of the stellar multiplicities with primary mass. We find for the F-and G-type Population. I stars that 58% are non-single and 21% are in triple or higher level systems. For the old intermediate-disk and Population. II stars-virtually all of G type and less massive -even two out of three sources prove to be non-single. These numbers being lower limits because of the continuous flow of new discoveries, the unbiased survey clearly demonstrates that the standard case for solar-type field stars is a hydrogen-burning source with at least one ordinary or degenerate stellar companion, and a surprisingly large number of stars are organized in multiple systems. A principal consequence is that orbital evolution, including the formation of blue straggler stars, is a potentially important issue on all spatial scales and timescales for a significant percentage of the stellar systems, in particular among Population. II stars. We discuss a number of recent observations of known or suspected companions in the local survey, including a new detection of a double- lined Ba- Bb subsystem to the visual binary HR 8635.