Luc Montagnier, a French virologist who shared a Nobel Prize in 2008 for discovering the virus that causes AIDS, passed away. He was 89. The discovery of H.I.V. began in Paris on Jan. 3, 1983. That was the day that Dr. Montagnier (pronounced mon-tan-YAY), who directed the Viral Oncology Unit at the Pasteur Institute, received a piece of the lymph node that had been removed from a 33-year-old man with AIDS.