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Astron. Astrophys. 354, 522-536 (2000)

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Local galactic kinematics from Hipparcos proper motions

F. Mignard

Observatoire de la Côte d'Azur, CERGA, UMR CNRS 6527, av. Copernic, 06130 Grasse, France

Received 4 October 1999 / Accepted 7 December 1999


The stellar velocity field within two kiloparsecs of the solar system is investigated from the Hipparcos proper motions and parallaxes of about 20 000 single stars farther than 100 pc. The motion of the sun relative to the Local Standard of Rest and the relative systematic velocity field due to the galactic rotation are studied simultaneously for several categories of stars ranging from early type dwarfs to K and M giants observed by Hipparcos. The relative velocity field is modeled in the framework of the Milne-Ogorodnikov hydrodynamic representation and led to the determination of eight parameters characterizing the flow, including the usual Oort Constants. The peculiar motion of these stars is also studied from the residuals and led to a new determination of the components of the velocity dispersion for every class of stars considered.

The components of the solar motion are ascertained to within [FORMULA] km s-1 in each direction and are found to vary significantly with the star sample, except for the component normal to the galactic plane always close to 7 km s-1. Regarding the Oort constants, one finds [FORMULA] km s-1kpc-1 for early type dwarfs and [FORMULA] km s-1kpc-1 for the distant giants. The constant B shows a less obvious difference with respectively [FORMULA] km s-1kpc-1 and [FORMULA] km s-1kpc-1. The galactic center is found to lag by 6 degrees from the normal to the direction of the galactic motion of the LSR in the solar neighborhood. Finally the three components of the velocity dispersion are determined and discussed for all the stellar groups considered in this paper with an accuracy of [FORMULA] km s-1.

Key words: astrometry – celestial mechanics, stellar dynamics – Galaxy: kinematics and dynamics – Galaxy: solar neighbourhood

Send offprint requests to: F. Mignard (mignard@obs-azur.fr)

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© European Southern Observatory (ESO) 2000

Online publication: February 9, 2000