We have conducted a full spectral line survey of the 3-13 micron region of two massive protostars, AFGL 2591 and AFGL 2136, for the first time at high spectral resolution. Utilising SOFIA/EXES... Show moreWe have conducted a full spectral line survey of the 3-13 micron region of two massive protostars, AFGL 2591 and AFGL 2136, for the first time at high spectral resolution. Utilising SOFIA/EXES observations, combined with ground based observations from TEXES and iSHELL, many transitions of HCN, C2H2, NH3, CS, CO and H2O are observed, with all species observed to be in absorption. High temperatures (600 K) and abundances (1-10e-6 w.r.t H) of each species are derived. In this thesis, I will present the new insights into the physical conditions and chemical composition of the disks that these absorption lines probe. In particular, hundreds of ro-vibrational transitions of H2O are detected with EXES towards each object, and are linked to a disk wind in AFGL 2591. Column density variations of HCN and C2H2 in bands that probe the same lower level, across different wavelengths, are also discussed, supporting the location of this gas in the circumstellar disk of these protostars. Finally emission lines of HCN are discussed towards MonR2 IRS 3 and are consistent with an origin in a circumstellar disk, or also possibly an expanding shell of gas, supported by P-Cygni profiles of CO lines. Show less
Multiple stars, that is two or more stars composing a gravitationally bound system, are common in the universe.They are the cause of many interesting phenomena, from supernovae and planetary... Show moreMultiple stars, that is two or more stars composing a gravitationally bound system, are common in the universe.They are the cause of many interesting phenomena, from supernovae and planetary nebulae, to binary black hole mergers. Observations of main sequence stars, young stars and forming protostars show that multiplicity is common, and that multiple stars are born. This thesis focuses on several of the open questions on the formation and evolution of multiple stars, namely when do rotationally supported disks form, the factors leading to fragmentation of the cloud core and the physico-chemical structure of multiple protostars. For this purpose, radio interferometric observations of dust continuum and molecular line emission, coupled with chemical and physical models are used to study several young, deeply embedded prototstars. The results of this thesis contribute useful pieces to the puzzle of multiple star formation, demonstrating that rotationally supported disks can form early in the star formation process, while temperature and the presence of disks can alter the physico-chemical protostellar structure. Furthermore, the results of this thesis indicate that mass, rather than temperature, could be an important factor in fragmentation of cloud cores, and the formation of multiple stars. Show less
Star and planet formation is intimately linked through the protostellar disk. Understanding the formation and evolution of this disk is crucial to determine the physical and chemical processes that... Show moreStar and planet formation is intimately linked through the protostellar disk. Understanding the formation and evolution of this disk is crucial to determine the physical and chemical processes that occur from the formation of dense molecular clouds to the emergence of life. Yet, the formation and early evolution of the protostellar disk are still not well explored. This thesis presents both observational and theoretical aspects of the early stages of disk formation and evolution. Hydrodynamical simulations of disk formation are coupled with multi-frequency continuum radiative transfer to determine the dust temperature. The detailed dust temperature structure is crucial for the construction of chemical structure. Observational predictions are simulated through molecular line radiative transfer methods to be compared with spectrally and spatially resolved data. By comparing these predictions with observational data, it is possible to link the disk formation process with planet formation Show less
