What is the highest number of school enrollment for Union Star High School in De Kalb county?
CREATE TABLE "list_of_member_schools" (
  "school" text,
  "team_name" text,
  "town" text,
  "county" text,
  "school_enrollment_2008_10" real,
  "football" text
);
SELECT MAX("school_enrollment_2008_10") FROM "list_of_member_schools" WHERE "county"='de kalb' AND "school"='union star high school';