Vilma Espin Guillois, the wife of acting President Raul Castro and one of the communist nation's most politically powerful women, died Monday, the Cuban government announced. She was 77. As Raul Castro's wife, Espin was Cuba's de facto first lady for decades because Cuban leader Fidel Castro is divorced. Authorities did not disclose Espin's illness, but she was said to suffer from severe circulatory problems in recent years and rumors about her poor health circulated periodically. An official mourning period was declared from 8 p.m. Monday until 10 p.m. Tuesday, and the Cuban flag will be lowered to half mast at all public buildings and military bases during that period, according to the official statement announcing Espin's death.