COMMUNICATIONS / MITTEILUNGEN
Structure of NGC 2420
No. 81
Budapest, 1982
Abstract
A new examination of the structure of NGC 2420 has been made according to
Kholopov's method. 1890 stars were measured between the circles of about 6'
and 25' radius centered on the cluster, for which photographic B,V magnitudes
and positions were obtained down to the limiting magnitude of plates (17.8 in
V) but in constructing the density distributions stars down to mag. 17.5 were
chosen. A literature determination of the proper motion of stars in a circle
of 12' radius was used to define the place and shape of the C-M diagram.
Around this diagram bands of 0.1, 0.2 and 0.3 magnitude width in B-V were
drawn to select the members of the cluster. The stars were separated into
four groups and surface density distributions were made for the whole cluster
and for each subgroup. The distributions of the stars reveal two different
parts of the cluster: the core has a radius of 5.1 pc, whereas the halo
extends as far as 12.7 pc. The brighter stars belong to the core and many of
fainter ones to the halo - as might expected from the theory. The whole halo
seems to be steady against the irregular forces of background stars but the
outer part of the halo from 8.2 pc radius is not stable against the tidal
force.
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