In a large pot, combine carcass, celery, carrots, onion, bay leaf and water and bring to a simmer. Simmer for 2 to 3 hours over medium low heat. Strain and discard vegetables and bones. Reserve turkey stock. In a large pot, melt butter and cook onions until tender. Stir in celery and thyme. Stir in carrots and rice and toss to coat. Stir in turkey stock and bring to a simmer. Cook until vegetables and rice are tender. Stir in turkey, corn and parsley. Return to simmer and season to taste.