My research projects Estimating the initial mass function of stars in very small systems.

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Background The initial mass function (IMF) of stars describes the distribution of masses of newborn stars, i.e., how likely it is that a newborn star has a certain mass. The IMF is a highly important connection between observation and theory. Theoretical models of star formation provide a prediction of the IMF and observations have to decide whether these predictions are compatible with reality or not. Moreover, it is commonly accepted to assume that the IMF is universal, i.e., it is the same everywhere in the universe at any given time. This assumption enables astronomers to estimate the star-formation rates and stellar masses of galaxies, which provide highly important diagnostics for studying the evolution of galaxies. What are the problems? The IMF is usually estimated by measuring the masses of numerous stars, e.g., in a globular cluster. There are several problems involved here: The masses of individual stars are not known precisely but only within certain errors. However, this is typically not taken into account. Usually, the mass distribution is binned and the IMF is estimated from the binned data. The mathematical form of the IMF is often chosen in an a-priori unphysical way. These effects restrict our knowledge about the IMF. In particular, these effects could obscure evidence for a non-universal IMF, which would have serious repercussions for the diagnostics in galaxy evolution. What am I doing? So far, I already have derived a mathematically well justified parametrisation of the IMF, which is not a-priori unphysical. Currently, I am developing a method to estimate the IMF without binning the data and taking into account the errors in stellar-mass estimates. I am applying this method to estimate the IMF of young stellar groups, containing only 10 to a few tens of stars. That would be plainly impossible with binning.