Orbits of globular clusters in the outer galaxy: NGC 7006

We present a proper-motion study of the distant globular cluster NGC 7006 b ased on the measurement of 25 photographic plates spanning a 40 yr interval . The absolute proper motion determined with respect to extragalactic objec ts is (mu (alpha) cos delta, mu (delta)) = (-0.96, -1.14) +/- (0.35, 0.40) mas yr(-1). The total space velocity of NGC 7006 in a Galactocentric rest f rame is 279 km s(-1), placing the cluster on one of the most energetic orbi ts (R-a = 102 kpc) known to date for clusters within 40 kpc from the Galact ic center. We compare the orbits-as determined from full space velocities-o f four clusters that have apocentric radii larger than 80 kpc with those of Galactic satellites with well-measured proper motions. These clusters are NGC 5466, 6934, and 7006 and Pal 13, and the satellites are the Sagittarius dwarf spheroidal galaxy (dSph), the Large Magellanic Cloud, the Ursa Minor dSph, and the Sculptor dSph. Only NGC 5466 and 6934 seem to have similar o rbital parameters, indicating a possible phase-space association. NGC 7006, Pal 13, and the "pair" NGC 5466 and 6934 do not show any dynamical associa tion with the Galactic satellites considered here. NGC 5466, 6934, and 7006 and Pal 13 have orbits that are highly eccentric and of various inclinatio ns with respect to the Galactic plane. In contrast, the orbits of the Galac tic satellites are of low to moderate eccentricity and highly inclined. Bas ed on orbit types, chemical abundances, and cluster parameters, we discuss the properties of the hypothetical host systems of the remote globular clus ters in the Searle-Zinn paradigm. It is apparent that clusters such as NGC 5466, 6934, and 7006 formed in systems that more likely resemble the Fornax dSph rather than the Sagittarius dSph. We also discuss plausible causes fo r the difference found so far between the orbit type of outer halo clusters and that of Galactic satellites and for the tentative, yet suggestive, pha se-space scatter found among outer halo clusters.