Friends of hot jupiters. I. A radial velocity search for massive, long-period companions to close-in gas giant planets

Heather A. Knutson, Benjamin J. Fulton, Benjamin T. Montet, Melodie Kao, Henry Ngo, Andrew W. Howard, Justin R. Crepp, Sasha Hinkley, Gaspar Á Bakos, Konstantin Batygin, John Asher Johnson, Timothy D. Morton, Philip S. Muirhead