The distance, structure, dynamics and age of the Hyades cluster have
been studied with Hipparcos data by Perryman et al. A compressed postscript or 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.
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.
You are now ready to see the Hyades movie!
This page was prepared by A.G.A. Brown
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Last update: 17 September 1997
(M.A.C. Perryman [Astrophysics Division - SSD])
