Radian Group shares slumped more than 10% Monday, retreating after the company unveiled a plan to raise up to $350 million in new capital, some of which will probably be used to support its mortgage-insurance business. Gina Chon says that AOL hired financial advisers to explore options for the company, one of which is a possible tie-up with Yahoo. Radian said it’s offering up to $350 million of convertible senior notes due 2017. Underwriters can buy another 15%, or $52.5 million, of the equity-linked debt if demand warrants, the company added.