Introduction to Star Clusters

From an observational point of view, clusters are localized concentration of stars that can make some sky regions more densely populated than others.

Stellar clusters have longh been regarded as important laboratiories for various type of research in stellar astronomy and astrophysics. Open clusters are important because they contain a statistically significant numbers of stars gravitationally bounded.

Studies in star clusters have given one of the major contribution in understanding, not only the structure and evolution of galaxies, but also to the knowledge of stellar evolution.

Selecting and studying a sample of clusters having different ages we can see how they evolve. The clusters color-magnitude diagrams are, in fact, the best templates at our disposal to study stellar evolution.

The stars members of clusters spanning over a wide range of masses and therefore of luminosities. Since the stars inside clusters appear to be physically associated, it is plausible to consider that they where born close thogether, at about the same time.

Using stellar models, we have improved the understanding of all the stars found in different evolutionary stages inside a cluster, such as: Yellow and Red Giants, Cepheids or RR Lyrae. In the same way, also the determination of cluster age, become possible.

An other important factor that can not be neglected is the evidently little depth of a clusters, depth that can be considered tiny, compared with its distance from the earth. So, under the previous assumption, all stars within a cluster can be considered, on average, at the same distance from us.

Star clusters are found in all three galaxy evironment, halo, disk and bulge. During their motion inside the various galactic evironments, the open clusters and the OB associations are gradually dispersed either by interactions with field stars or by collision with interstellar clouds.

Observations, such as homogeneity in members and common motions show, whit no doubt, that they were born out of the same cloud of interstellar gas through a fragmentation process of the cloud itself.

This last observation has another immediate consequence: the members of a star cluster must have, more or less, the same chemical composition.

Along this entire site, with only few exceptions, we have accurately avoided connections to images of various open clusters and more generally, to all other information otherwise easy obtainable on line.

With this choice, and in order to help amateurs to lead a nearly professional job over this field, we have tried to privileged more deep technical aspects, supplying amateurs searches, with a devoted software.

© 2006 - Valter Arnò.