Reuters (Nasdaq:RTRSY), in the process of merging with Thomson, has bought an investment research firm StarMine, for an undisclosed sum. San Francisco-based StarMine is a provider of analytics and equity research tools and performance ratings to securities analysts. Founded in 1998, StarMine had gross assets of $16.3 million as of June 30, the company said. The company has investment from Hummer Winblad Venture Partners, Instinet and American Century Ventures.