THE ASTROPHYSICAL JOURNAL, 564:1028È1034, 2002 January 10 ( 2002. The American Astronomical Society. All rights reserved. Printed in U.S.A. A SECOND PLANET ORBITING 47 URSAE MAJORIS1 DEBRA A. FISCHER,2 GEOFFREY W. MARCY,2 R. PAUL BUTLER,3 GREGORY LAUGHLIN,4 AND STEVEN S. VOGT5 Received 2001 June 29 ; accepted 2001 September 13 ABSTRACT Precise Doppler velocity measurements during 13 yr at Lick Observatory reveal the presence of two planets orbiting the star 47 UMa. The previously detected inner planet is conÐrmed by the newer veloci- ties that yield a revised orbital period days, M sin i \ 2.54 and eccentricity P b \ 1089.0 ^ 2.9 M J , e b \ 0.061 ^ 0.014. The residuals to that single-Keplerian Ðt exhibit a periodicity that is consistent with an additional planetary companion. A simultaneous Ðt for both planets implies that the outer planet has days, a \ 3.73 AU, and M sin i \ 0.76 Its semimajor axis is the largest P c \ 2594 ^ 90 0 \ e c \ 0.2, M J . yet found for an extrasolar planet, and its angular separation from the host star of makes it a good 0A .26 target for direct detection and astrometry. Hipparcos astrometry places limits on the masses of these planets at less than D10 and dynamical modeling places limits on both and the orbital inclina- M J , e c tions. The outer planet induces a velocity semiamplitude of K \ 11.1 m s~1 in the star during its 7 yr orbit, similar to the signal induced on the sun by Jupiter. Subject headings : planetary systems È stars : individual (47 Ursae Majoris) 1. INTRODUCTION Since 1995, D70 gas giant extrasolar planets have been discovered in Doppler surveys of solar-type stars (see Butler et al. 2001, Mayor et al. 2001 ; Naef et al. 2001). This ensem- ble of extrasolar planets is characterized by a mass distribu- tion that rises toward the low-mass detection threshold, currently D0.2 (Marcy & Butler 2000 ; Jorissen, Mayor, M J & Udry 2001). The Doppler technique may be detecting only the most massive planets, missing those with masses below 0.2 M J . Unlike planets in our solar system, the Doppler-detected planets tend to reside either in close-in or eccentric orbits. These characteristics are presumed to result from dynami- cal migration and some mechanisms that have been pro- posed are tidal interactions between the protoplanet and the disk (Goldrich & Tremaine 1980 ; Lin, Bodenheimer, & Richardson 1996 ; Bryden et al. 1999), gravitational scat- tering between growing planetesimals (Rasio & Ford 1996 ; Weidenschilling & Marzari 1996 ; Levison, Lissauer, & Duncan 1998) and resonant gravitational interactions between planets and planetesimals in the disk (Murray et al. 1999 ; Murray, Hansen, & Holman 2001). Migrating gas giant planets have evidently su†ered a more violent history of dynamical evolution than the planets in our solar system. The maximum semimajor axis of detected extrasolar planets is currently D3 AU and is set by the time baseline of Doppler surveys. As the time baselines of these surveys grow, the eccentricities of planets at larger separations will be revealed, allowing direct comparison with the giant planets in our solar system. Planetary systems with gas giant planets in circular orbits may Ñag analogs of our solar system. 1 Based on observations obtained at Lick Observatory, which is oper- ated by the University of California. 2 Department of Astronomy, University of California, Berkeley, CA 94720 ; Ðscher=serpens.berkeley.edu. 3 Department of Terrestrial Magnetism, Carnegie Institution of Wash- ington, 5241 Broad Branch Road NW, Washington, DC 20015-1305. 4 NASA Ames Research Center MS 245-3, Mo†ett Field, CA 94035. 5 UCO/Lick Observatory, University of California at Santa Cruz, Santa Cruz, CA 95064. Models of planet formation predict that multiple planets should form within the protoplanetary disk around a young star (see Lissauer 1995). This prediction constitutes a test of the true planet status of the Jupiter-mass companions found to date, and it established a testable link to our solar system architecture. The Ðrst extrasolar multiple planet system was discovered around Upsilon Andromedae (Butler et al. 1999), and since then, double planet systems have been detected around HD 83443 (Mayor et al. 2001), HD 168443 (Marcy et al. 2001a ; Udry, Mayor, & Queloz 2001), and GJ876 (Marcy et al. 2001b). Residual velocity trends in known planet-bearing stars suggest that additional planet- ary companions may ultimately be found in more than half of the stars with one detected planet (Fischer et al. 2001). Multiple planet systems that undergo short-term gravita- tional perturbations o†er an opportunity to constrain the companion masses (Laughlin & Chambers 2001 ; Rivera & Lissauer 2001 ; Lissauer & Rivera 2001 ; Chiang, Tabachnik, & Tremaine 2001). 2. STELLAR CHARACTERISTICS 47 UMa (\HR 4277, HD 95128, HIP 53721) is a G0V star with V \ 5.03, B[V \ 0.624, and Hipparcos (ESA 1997) parallax of 71.04 mas. We have carried out an LTE synthesis of its spectrum and Ðnd K, T eff \ 5780 v sin i \ 1.85 km s~1, and [Fe/H] \]0.01, consistent with published values (Gonzalez 1998). We measure Ca II H and K core emission, on the Mount Wilson Scale S HK \ 0.142, (Noyes et al. 1984), which implies a ratio of the H and K Ñux to the bolometric Ñux of . These values of log R HK @ \[5.12 chromospheric S and agree with those of Henry et log R HK @ al. (1997), Baliunas et al. (1998), and Henry et al. (2000). These chromospheric indices correlate well with stellar rotation (Noyes et al. 1984) and age (Baliunas et al. 1995), yielding a rotation period, P \ 24 days and an age of D7 Gyr. The star shows no signiÐcant variability in either its broadband optical brightness or Ca II H and K emission (Henry et al. 1997, 2000). We are not aware of any detection of a magnetic (spot) cycle for this old star, and 3 yr of photometry have yielded no variation above 1 mmag (Henry et al. 2000). 1028