Stars like the sun are born in large molecular clouds existing from gas and dust. During the formation process, the chemical composition of the material can be altered drastically by the changing... Show moreStars like the sun are born in large molecular clouds existing from gas and dust. During the formation process, the chemical composition of the material can be altered drastically by the changing physical conditions. This thesis focuses on how molecules in young protostellar systems are inherited from molecular clouds. The emphasis lies on so-called complex organic molecules and accretion shocks.Based on observations of complex organic molecules, it can be suggested that the molecular composition of a protostellar disk is (partially) inherited from the molecular cloud. The abundance ratio between various molecules is remarkably constant in various protostellar systems, implying that they form under similar conditions in molecular clouds. Furthermore, absence of complex molecules in observations does not directly mean that they are absent in the protostellar system but rather that they are hidden from us.This thesis also focuses on accretion shocks at the boundary between infalling cloud and protostellar disk. Based on a comparison between detailed numerical simulations and observations it can be suggested that strong accretions are not always present in protostellar systems. In turn, this suggests that the chemical composition in protostellar disks can be directly inherited from the molecular cloud. Show less
Nazari, P.; Meijerhof, J.D.; Gelder, M.L. van; Ahmadi, M.; Dishoeck, E.F. van; Tabone, B.; ... ; Schilke, P. 2022
The focus of this thesis is how stars like our Sun and planets like Jupiter, Saturn, and Earth are formed. With arrays of radio telescopes, I observed the environments where the first stages of... Show moreThe focus of this thesis is how stars like our Sun and planets like Jupiter, Saturn, and Earth are formed. With arrays of radio telescopes, I observed the environments where the first stages of star and planet formation occur. This thesis focuses on characterizing different components of young protostellar systems, most notably their jets and disks. Using interferometric radio observations with ALMA array, I provided information on key chemical tracers of different components of the protostellar systems. By characterizing the radio signal from young stars with ALMA and VLA interferometers, I was able to disentangle an emission from the jet and the disk. This led to an unexpected development: I was able to compare dust masses of young disks with those of older disks for the first time. By comparing this information with masses of the extrasolar planets detected so far I showed that the solid cores of gas giants must form in the first 0.1 Myr of stellar life. That is an important time constrain, that pushes the onset of planet formation earlier and highlights the importance of characterization of the youngest protostars in understanding the origin of Solar System and Earth. Show less
To address the fundamental questions of how life on Earth emerged and how common life may be in the Universe, it is crucial to know the chemical composition of the planet-forming material. Planets... Show moreTo address the fundamental questions of how life on Earth emerged and how common life may be in the Universe, it is crucial to know the chemical composition of the planet-forming material. Planets were originally thought to form in protoplanetary disks, but studies of both disks and our Solar System show that planet formation already starts much earlier, in disks that are still embedded in cloud material. These young disks, however, are largely uncharacterised. This thesis presents a number of case studies on the physical and chemical structure of young disks, including the first temperature measurements showing that young disks are too warm for CO ice, unlike protoplanetary disks. In addition, it is shown that young disks around outbursting stars are the ideal sources to probe the the chemical complexity in planet-forming material. Show less
This thesis is centered around the embedded phase of star formation and the chemical links between the various stages of evolution. The primary goal of this work is to pinpoint the origins... Show more This thesis is centered around the embedded phase of star formation and the chemical links between the various stages of evolution. The primary goal of this work is to pinpoint the origins of cometary complex organic molecules in the preceding protoplanetary disk and prestellar stages, both in the gas and solid phases. The grand motivation is to identify our interstellar roots. This work is unique in comparison to earlier publications due to the dynamic nature of the models used in combination with the large comprehensive chemical network. Three chapters in this book pertain to physicochemical models and an additional one is of observational nature. Altogether, this thesis is an attempt to piece together the chemical connection between the prestellar core, the protoplanetary disk and the protoplanetary and cometary materials. The main take-home message is that the seeding of infant Solar System building blocks with complex organic molecules is unavoidable as a result of chemistry during protoplanetary disk assembly. Show less
This thesis presents the results from the analysis and characterisation of the water and mid-J (J<11) 12CO, 13CO and C18O observations for a large sample of low-, intermediate-, and high-mass... Show moreThis thesis presents the results from the analysis and characterisation of the water and mid-J (J<11) 12CO, 13CO and C18O observations for a large sample of low-, intermediate-, and high-mass young stellar objects (YSOs). The studied molecular transitions have been observed with the HIFI instrument on board of Herschel Space Observatory and within the context of the Herschel key programme __WISH__. These species and transitions constitute unambiguous tracers of specific physical conditions within the inner and warmer regions of the YSO environment. The sample of sources, composed by more than 120 YSOs, covers a large range of bolometric luminosities, several evolutionary stages within the embedded phase, and different physical scales. The aim of this work is to explore the differences and similarities between low- and high-mass star-forming regions. In particular, this study focuses on investigating the physical and dynamical structure of dense warm gas within protostellar environments by characterising the velocity-resolved H2O and CO spectra in terms of line profile and line luminosity. The ultimate goal is to contribute to the understanding of the star formation process without imposing luminosity boundaries, and to put in context these processes on Galactic and extragalactic scales. Show less
The primary focus of this thesis is the formation of low-mass protostars, specifically the earliest deeply embedded phase, when material from the collapsing envelope is still accreted onto the... Show moreThe primary focus of this thesis is the formation of low-mass protostars, specifically the earliest deeply embedded phase, when material from the collapsing envelope is still accreted onto the growing young star. Rotational transitions of CO and O2 data are obtained by the Herschel Space Observatory key projects, WISH and HOP, together with ground-based observations from APEX and the JCMT. We have found that CO and its isotopologs have different line profiles tracing different materials in the protostellar regions. Our new high-J rotational transitons of CO is key to characterize the warmer parts of the protostellar envelope and quantify feedback of the protostars on their surroundings in terms of shocks, ultraviolet (UV) heating, photodissociation, and outflow dispersal. Radiative transfer modeling was performed to determine the CO abundance structure in the envelope, showing evidence for significant freeze-out in the coldest regions in the parts of the envelope where the temperature exceeds 25 K. A tentative detection of O2 is reported toward the source position of a protostar, which originates from the surrounding cloud. These kind of detailed studies of the physical and chemical structure of low-mass protostars are important for a complete understanding of the evolution of young stellar objects (YSOs). Show less
