Coffee talks
Friday 25/10/2019 @ 11:30, Sala Padrielli
Elena Redaelli (Max Planck Institute for Extraterrestrial Physics), "Molecular fractionation in the low-mass star forming regions"
Fractionation is the substitution of an atom in a molecule with one of its isotopes, creating a so-called isotopologue. In the last decades, this process has raised great interest, because it is considered an important diagnostic tool to follow the different phases of star formation, from its early stages up to the planetary disk formation and evolution. In my work, I focus on the fractionation of two of the most abundant atoms in the Universe, hydrogen and nitrogen. In my talk I will report observations of different isotopologues of N2H+ and HCO+ in a small sample of prestellar cores. These objects, which are cold (T~5-10K) and dense (n > 10^5cm-3), formed through the fragmentation of molecular clouds, and they represent the very early stages of low-mass star formation. We have observed the rotational transitions of N2H+ and HCO+ using the IRAM 30m telescope. From these data, I have derived reliable values of the molecular column density of each species. I then infer the searched isotopic ratio dividing the rare isotolopogue column density by that of the corresponding main species. Concerning nitrogen fractionation, I find that all the sources present 15N/14N ratio significantly lower than the Solar System value, a result which cannot be understood in the frame of the state-of-art chemical models. On the contrary, the D/H ratios found in N2H+ and HCO+ (26% and 3.5% respectively) can be explained by the different chemistry that these two ions exhibit.