The Mass Function and mass segregation in nearby open clusters

"The most important parameter defining the evolution of a star is its mass. We call this mass distribution in star clusters as the Initial Mass Function (IMF). In an open cluster, the IMF is far from straightforward to understand due to observational limitations. In addition, primordial binary stars, gas remnants and the star formation efficiency may produce biases in the slopes for different mass ranges, if they are not included. In particular, at the low-mass extreme the number of stars increases, their masses are not well characterised, and the most common way to produce estimates is by interpolation. On this basis, it is possible to study the mass segregation effect, in which the most massive stars are found in the centre of the cluster. This provides details about the dynamical state of the open cluster. Forthcoming catalogues, such as the LSST, will provide very good observations beyond the Gaia limit, and promise to unveil the faint stellar population.

From recent work, Alfonso et al. (2024) produce a list of 87708 bona fide members in 370 nearby open clusters using Gaia Data Release 3 up to G=19.8 mag. Based on this sample, we infer the masses of stars in some open clusters using the Gaia Astrophysical Parameters. We interpolated the mass distribution by reaching about 0.3 solar masses, thus constructing the IMF and fitting a power-law with comparable results from the literature. From the inferred masses, we also study the mass segregation effect by constructing the minimum spanning tree of the most massive stars in these open clusters. We show that in three particular clusters segregation is clearly observed, thus providing clues about the early expansion and dynamical properties of relatively young open clusters."