AN INVESTIGATION OF THE CepOB6 ASSOCIATION
ROBERT KAMBEN
University of Troms., Norway
and EVSTIGNEEVA EKATERINA
St. Petersburg State University, Russia
1. Introduction
O and B stars are not distributed randomly on the sky, but instead they are concentrated
in loose groups, that are called "OB associations".From dynamical point of view it follows that OB assotiations should be young (=< 50Myr), a conclusion supported also by the ages
derived from color- magnitude diagrams. OB associations are the stellar groupings of low
density (usually less then 0.1 MSunpc-3 such that they are likely to be unbound. Their projected dimensions range from ~10 to ~100 pc. Observations of molecular cloudes indicate that these groups are usually located in or near starforming regions, and hence are prime
sites for the study of star formation processes and of the interaction of early-type stars
with the interstellar medium. In the context of star formation a detailed examination of
the stellar content, structure, and kinematics of OB associations allows us to address the
following fundamental questions: What is the initial mass function? What are the charac-
teristics of the binary population? What causes the distinction between the formation of
bound open clusters and unbound associations? How is angular momentum redistributed
during star formation? What is the resulting distribution of rotational velocities of stars?
etc.
2. Cep OB6 assooiation
We have investigated the CepOB6 association. This association has been recently discovered on the basis of the Hipparcos data [2].The center of this association almost coincides
with the position of classical cepheid delta Cep. It occupies the region 100° < l < 110° and -4° < b < 3°. The aim of investigation:
-To study distribution of interstellar dust in this region.
-To search for the new members of the association on the basis of obtained photometric data.
We have chosen 18 stars from this association. Observations were made with the 63 cm telescope during period of 01.09.99 - 08.09.99. We used Vilnius photometric system. Extra-atmospheric reductions of observations have been made using program package EXATMOS developed at the Institute of Theoretical Physics and Astronomy. Classification of stars have been carried out using program CLASS developed at the Institute of Physics. The program CLASS derives MK spectral types and calculates color excesses, intrinsic color indices and distances of stars.
The distribution of interstellar matter is shown in Fig.1. After HIPPARCOS data, filled
squares are stars that are association members, and empty squares indicate non members.
About 0.1 kpc from Sun there is interstellar dust cloud. Distribution of interstellar matter
in this region is non uniform. At a distance of the association interstellar extinction varies
in the range of 0 - 0.6 mag. H-R diagram for observed stars is plotted in Fig.2 .It is
seen on this diagram that the majority of stars are located in the left lower region of the
diagram along the main sequence. But one star that after HIPPARCOS data is not in
association was found perfectly lying in it, therefore belonging to it. And one star that
after HIPPARCOS data is in CepOB6 in our data falls out. Three most luminous members
are older and therefore go to the right side of the diagram.
Figure 1. The distribution of interstellar matter in the region of the CepOB6.
Figure 2. H-R diagram for the CepOB6.
References:
1. The Origin of Stars and Planetary Systems: Proceedings of the NATO ASI, eds. C.J.Lada,
N.D.Kylafis, Volume 540, 1999 (in print).
2. De Zeeuw P.T. et al, Astron.J., 117, 354-399 (1999)
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