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Accuracy of the stellar transverse velocity
The astrometric solution of Gaia will provide accurate estimates for the distances (through the parallaxes) and the annual proper motion of the stars in our Galaxy. The accuracy is primarily a function of the star brightness, as shown in the Performances Pages. By combining the distance and the annual angular displacement on the sky, one can deduce the actual transverse velocity in km/s. The uncertainty of this determination is assessed by propagating the contribution of the uncertainties on the parallax and the proper motion for different categories of stars, as a function of either their distance or their magnitude in the G-band.
The two plots illustrate the expected performances for a representative sample of stellar types. The left plot gives the uncertainty in the transverse velocity in km/s as a function of the G magnitude, with an indication of distances at G =15. The right plot displays the same data as a function of the distance in pc, with indication of magnitude at d = 1 and 3 kpc. Each curve is labelled by a spectral type, and the floor of 1 km/s of the RVS performance in radial velocity is highlighted.
Details on the derivation can be found in the technical note (restricted access).
Copyright: F. Mignard
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