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A 40' x 70' FIELD AROUND TRUMPLER 3
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Among Galactic open clusters there are objects which basic parameters such as an age or distance still remain
unknown. In this paper we present photometric and spectroscopic investigations of Trumpler 3 (C 0307+630
= Harvard 1) - a poor, low-contrast open cluster located in the constellation of Cassiopeia. The existence of
an open cluster in the area occupied by Trumpler 3 was postulated by Barnard at al. (1927). Trumpler (1930) described
the cluster as a very loose open cluster, not rich but regular in outline and structure. Moreover, the author
classified this stellar ensemble as a cluster of type II3p and determined the angular diameter of 17' and the
distance of 0.69 kpc. Ruprech (1966) classified Trumpler 3 as a poor cluster of class III3p. According to the
New catalogue of optically visible open clusters and candidates by Dias et al. (2002), the angular diameter
of the cluster is 14'. Kharchenko at al. (2005) performed the first photometric studies of the cluster but they
were limited to stars brighter than V=12-13 mag. The authors obtained the limiting radius of 30', the core
radius of 8', the age of 220 Myr, and the apparent distance modulus of 8.95 mag which they converted to the distance
of 450 pc. Moreover, the interstellar reddening E(B-V) was found to be 0.22 mag. Mermilliod at al. (2008) measured
the radial velocities for two stars - members of the cluster - and determined the mean radial velocity of the
cluster.
No dedicated CCD studies of Trumpler 3 have been performed to date. To fulfill this niche, we gathered wide-field
deep BV photometry and combined it with near-infrared JHK photometry extracted from the 2-Micron All Sky Survey.
Basic parameters such as the age of 70±10 Myr, the color excess E(B-V)=0.30±0.02 mag, the distance
of 0.69±0.03 kpc and the limiting radius of 12' were redetermined. The distance of 0.65±0.09 kpc
was determined independently by spectral parallaxes. The distribution of interstellar extinction in the cluster field
suggests the existence of a bubble of interstellar matter associated with the cluster. Our analysis allowed us to
estimate a total number of members to be 570±90 and a total mass of
the cluster to be 270±40 Sun masses. We also determined a state of cluster's dynamical
evolution. We conclude that Trumpler 3 is a young low-massive stellar ensemble with a typical mass function slope,
located near to the outer edge of the Galaxy's Orion Spur. As a result of a wide-field search for short period
variable stars, 24 variables were discovered in the cluster's area. Only one of them -- a variable of the gamma-Dor type -- was found to be a likely cluster member.
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THE COLOUR-MAGNITUDE DIAGRAMS FOR TRUMPLER 3
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