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Astrometric radial velocities
I. Non-spectroscopic methods for measuring stellar radial velocity *
Lennart Lindegren and
Received 11 February 1999 / Accepted 26 May 1999
High-accuracy astrometry permits the determination of not only stellar tangential motion, but also the component along the line-of-sight. Such non-spectroscopic (i.e. astrometric) radial velocities are independent of stellar atmospheric dynamics, spectral complexity and variability, as well as of gravitational redshift. Three methods are analysed: (1) changing annual parallax, (2) changing proper motion and (3) changing angular extent of a moving group of stars. All three have significant potential in planned astrometric projects. Current accuracies are still inadequate for the first method, while the second is marginally feasible and is here applied to 16 stars. The third method reaches high accuracy ( km s-1) already with present data, although for some clusters an accuracy limit is set by uncertainties in the cluster expansion rate.
Key words: methods: data analysis techniques: radial velocities astrometry stars: distances stars: kinematics Galaxy: open clusters and associations: general
Online publication: August 13, 199