The Jupiter Twin HD 154345b

We announce the discovery of a twin of Jupiter orbiting the slightly metalpoor ([Fe/H] = −0.1) nearby (d= 18 pc) G8 dwarf HD 154345. This planet has a minimum mass of 0.95 MJup and a 9.2 year, circular orbit with radius 4.2 AU. There is currently little or no evidence for other planets in the system, but smaller or exterior planets cannot yet be ruled out. We also detect a ∼ 9-year activity cycle in this star photometrically and in chromospheric emission. We rule out activity cycles as the source of the radial velocity variations by comparison with other cycling late-G dwarfs. Subject headings: planetary systems — techniques: radial velocities Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology. The Keck Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Department of Astronomy, 610 Space Sciences Building, Cornell University, Ithaca, NY 14853 [email protected] Department of Astronomy, 601 Campbell Hall, University of California, Berkeley, CA 94720-3411 [email protected] Department of Terrestrial Magnetism, Carnegie Institute of Washington, 5241 Broad Branch Road NW, Washington, DC 20015-1305 [email protected] UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 [email protected] Center of Excellence in Information Systems, Tennessee State University, 3500 John A. Merritt Blvd., Box 9501, Nashville, TN 37209, USA [email protected] Department of Physics and Astronomy, San Francisco State University, San Francisco, CA 94132 [email protected] Townes Fellow, Space Sciences Laboratory, UC Berkeley [email protected]