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Study of the very low mass main sequence stars in open clusters

Technical requirements: V, I images down to a limiting magnitude of $V\sim27.5$ ( $I\sim 25.5$) in a $1\times1$ square degrees field.

To fully understand the star formation it is important to know what the end result of the process is. In particular, it is important to understand how predictable the star formation process is and whether or not the same frequency distribution of stellar masses will arise from the fragmentation of molecular clouds. We also need to address the question on whether or not the star formation processes differ in various part of the Galaxy. The most useful tool to address the above problems is the initial mass function (IMF), defined as the number of stars formed per mass interval. Mainly, the IMF has been discussed in terms of field stars. However, there are still many uncertainties in getting a reliable IMF from field stars, as extensively reviewed by Scalo (1986). On the other side, young star clusters represent ideal laboratories in which the IMF can be directly obtained from the present day (observed) luminosity function (LF). Star clusters give an unique opportunity of investigation of the stellar content for groups of stars of known distance and age and formed in the same formation act. And they allow to investigate the IMF from many solar masses down to $m\leq 0.1m_\odot$. The problem of the low mass stellar content of star clusters is of special interest: it is very important not only for understanding the star formation processes, but also for the determination of the total cluster mass, for understanding the cluster dynamical evolution, and because it can give hints on the fraction of the baryonic matter we should expect in form of low mass objects. In the case of open clusters, a large field is even more important than in the previous application on GGCs, because open clusters are spread out and because it is of fundamental importance to have a good coverage of the field surrounding the cluster for a statistically significant evaluation of the foreground/background contamination (Seleznev 1994). A large size telescope is again of fundamental importance, in view of the faintness of the very low mass main sequence stars, as a consequence of the steepening of the mass-luminosity relation. The numbers in terms of limiting magnitude are not very different from the ones given in the previous section for the closest GGC. Instead, the field size must be significantly larger, particularly in view of the large needed in order to accurately map the background/foreground contamination.


next up previous contents
Next: Mass segregation in open Up: Stellar populations Previous: Open Clusters
Guido Buscema
1999-01-29