Abstract
The Galactic disk velocity field in a 500 pc radius solar neighborhood is mapped on the basis of a set of 75,000 stars at an altitude lower than 300 pc above the Galactic plane and with a 55 km/s mean transverse velocity. An age range of 5 Gyr is inferred from the ellipsoidal distribution of the velocities in the Galactic plane. A circular motion with an expansion of 21 +/-12 km/s kpc was observed, suggesting a nonflat rotation cure, even when the young Gould's Belt stars are removed. A velocity gradient of 0.3 km/s pc delineates the shock front of large known clouds in the Pleiades, the Hyades, the Perseus, and the Scorpio-Ophiucus regions, suggesting that the Galactic differential rotation parameters describing stellar streaming cannot be segregated from the interstellar medium velocity. A transverse velocity dispersion increase of 3 km/s over a 50-pc cell size is noticeable in the Pleiades only. An 8 +/-4 km/s heating process of the local stellar disk during an encounter with dust clouds near an 18 +/-4 km/s transverse velocity is suggested.
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