Edward Kennedy was first elected to the Senate in 1962

After a six-day auction, they were secured by the publishers Twelve and are due to be published in 2010.

Industry sources told US media the deal was comparable to the $8m Sen Hillary Clinton got for Living History.

Sen Kennedy was first elected in 1962. His brother John F Kennedy had been elected president.

The Massachusetts senator has become an iconic figure within the Democratic Party, and a prominent campaigner for reforms in many areas, including education, wages, health care and immigration.

Twelve is part of the Hachette Book Group USA.