Hyades in 3D
(This page was prepared by A.G.A. Brown )
Click here to see the hyades movie. The distance, structure, dynamics and age of the Hyades cluster have been studied with Hipparcos data by Perryman et al. A pdf version of that paper is available online. Below the spatial structure of the Hyades is summarized. This structure is now for the first time mapped in 3 dimensions from directly measured distances (parallaxes) for each individual member of the Hyades.
The image above shows the projected positions of the 218 Hyades members in Galactic coordinates. The Sun is at (X,Y,Z)=(0,0,0), The negative X-axis is towards the Galactic anti-centre, and the positive Y-axis is in the direction of Galactic rotation. The red circle show the tidal radius (about 10 pc) of the cluster. Note that about 85 stars are located beyond the tidal radius, of which about 45 are located between one and two tidal radii.
Note that the appearance of this page, the images, and the movie may differ quite a bit from what I had intended, depending on the type of machine you're on, its screen, and the www-browser.
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These two images are frames from the Hyades movie which can be found below. The left image shows the first frame and shows the 3D structure of the Hyades as seen from the position of the Sun in Galactic coordinates. In terms of the X-Y diagram above we are looking down the X-axis towards the centre of the Hyades. Note that all spheres, representing the stars, are of the same size. Anything that appears bigger is thus physically closer to us. In the movie you will see the Hyades rotate around the Galactic Z-axis. The right image above shows the Hyades rotated over 315 degrees and some extra items are added. The green circle is the tidal radius of 10 pc and the yellow stars are members of Eggen's moving group. They are not considered members of the Hyades according to Perryman et al., but are shown here to give an impression of where one may find moving group stars. The last 20 frames of the Hyades movie show the motions of the stars within the cluster as inferred from the residual velocities with respect to the centre of mass motion of the cluster. The time steps are 50.000 years. Note that these motions are not representative of the true internal motions in the cluster. All the motions in the movie can be explained as observational errors. They are shown simply to convey the fact that velocities for all these stars are known. For details on the spatial and kinematic structure of the Hyades please refer to Perryman et al.