Cook pasta in lightly salted boiling water until al dente, tender but still firm. Drain.
While pasta is cooking, prepare the sauce. In a medium-size saucepan, bring cream and minced onion to a boil. Stir in asparagus and salmon. Heat through. Turn off heat and stir in 1/2 cup of the cheese, salt and cayenne.
Toss linguine with the sauce, top with remaining cheese and serve immediately.
