Structure of evolved cluster-forming regions

Context. An approach towards understanding the formation of massive stars and star clusters is to study the structure of their hot core phase, an evolutionary stage where dust has been heated, but molecules have not yet been destroyed by ultraviolet radiation. These hot molecular cores are very line-rich, but the interpretation of line surveys is also hampered by poor knowledge of the physical and chemical structure. Aims. To constrain the radial structure of high-mass star-forming regions containing hot cores, we attempt to reproduce by radiative transfer modeling both the intensity and shape of a variety of molecular lines. Methods. We observed 12 hot cores with the Atacama Pathfinder EXperiment (APEX) in lines of HCN, HCO+, CO, and their isotopologues, including high-J lines and vibrationally excited HCN. We investigate how well the sources can be modeled as centrally heated spheres with a power-law density gradient, making use of the radiative transfer code RATRAN and the radial profile of the submm continuum emission, taken from the APEX Telescope Large Area Survey of the GALaxy (ATLASGAL). Results. Most of the observed lines have complicated shapes that incorporate self-absorption, asymmetries, and line wings. Vibrationally excited HCN is detected in all sources, and vibrationally excited H13CN in half of the sources. We are able to successfully model most features seen in the APEX data, such as the ratio of the isotopologue lines (very high optical depths), self-absorption (temperature gradient), blue asymmetries (moderate infall), vibrationally excited HCN (high inner temperatures), and H13CN (high HCN abundance under dense and hot conditions). Other features could not be reproduced, such as an occasional lack of self-absorption, the emission from high-J lines in the outer pixels of the CHAMP+ receiver (15′′−20′′ from the center), the outflow wings, and the red asymmetric profiles. Conclusions. The amount of molecular gas, in particular of HCN, at very high temperatures is larger than previously thought. A complex interplay between infall and outflow motions is present. Our basic model assumptions of pure central heating and a power-law radial density distribution can serve as approximations for most sources, but are too simple to explain all observed lines. In particular, taking into account clumpiness, multiplicity of heating sources and a more complex velocity field seems to be necessary to more closely match model calculations to observations. This would require three-dimensional radiative transfer modeling of high-resolution interferometric data

An unbiased spectral line survey toward R CrA IRS7B in the 345 GHz window with ASTE

We have conducted a spectral line survey in the 332 - 364 GHz region with the ASTE 10 m telescope toward R CrA IRS7B, a low-mass protostar in the Class 0 or Class 0/I transitional stage. We have also performed some supplementary observations in the 450 GHz band. In total, 16 molecular species are identified in the 332 - 364 GHz region. Strong emission lines of CN and CCH are observed, whereas complex organic molecules and long carbon-chain molecules which are characteristics of hot corino and warm carbon-chain chemistry (WCCC) source, respectively, are not detected. The rotation temperature of CH3OH is evaluated to be 31 K, which is significantly lower than that reported for the prototypical hot corino IRAS 16293-2422 (~85 K). The deuterium fractionation ratios for CCH and H2CO are obtained to be 0.038 and 0.050, respectively, which are much lower than those in the hot corino. These results suggest a weak hot corino activity in R CrA IRS7B. On the other hand, the carbon-chain related molecules, CCH and c-C3H2, are found to be abundant. However, this source cannot be classified as a WCCC source, since long carbon-chain molecules are not detected. If WCCC and hot corino chemistry represent the two extremes in chemical compositions of low-mass Class 0 sources, R CrA IRS7B would be a source with a mixture of these two chemical characteristics. The UV radiation from the nearby Herbig Ae star R CrA may also affect the chemical composition. The present line survey demonstrates further chemical diversity in low-mass star-forming regions.Comment: 45 pages, 5 figures, accepted for publication in Ap

Putative changes in dopaminergic neurotransmission following nicotine induced behavioural sensitisation

Behavioural sensitisation is a progressive enhancement of stereotypic or locomotor behaviour following repeated intermittent administration of a psychostimulant or stress. It is a phenomenon thought to underlie many neuropsychiatric disorders (e.g. schizophrenia, addiction, depressive disorders, dyskinesia, and psychosis) although its own mechanism remains contentious. In this thesis a multidisciplinary approach was used to investigate the role of dopamine in behavioural sensitisation. Different in vivo and ex vivo techniques were used to assess and elucidate putative changes in dopaminergic neurotransmission of behaviourally sensitised animals. If so, this improved understanding of behavioural sensitisation could provide a better understanding of the pathophysiologies of neuropsychiatric disorders and provide more insight into why existing pharmacotherapies for these disorders are able to confer only modest benefit. Moreover, this improved understanding can lead to development of new medication and more effective therapies to treat neuropsychiatric disorders and therapies that address the specific problems associated with them. Previously, an oversimplified view of neurotransmitter release was used for the development of current available drugs, i.e. stabilising either the attenuated or increased release of neurotransmitters without considering the involvement of synaptic plasticity. Therapies being used with modest effectiveness regulate dopamine transmission levels, suggesting a putative role for dopamine. The present study used chronic intermittent nicotine administration in rodents to induce behavioural sensitisation which was monitored behaviourally by measuring locomotor activity. Further studies were performed ex vivo assessing receptor binding, intracellular cAMP accumulation and electrically stimulated dopamine release. Prior to the pharmacological assessments, a novel LC-MS/MS method to measure (cyclic-) nucleotides was developed and a fast cyclic voltammetry (FCV) technique was established to measure real-time neurotransmitter release. Specific pharmacological tools were used to identify the role of dopaminergic neurotransmission in behavioural sensitisation. Finally, the ex vivo findings using tissue from sensitised and non-sensitised animals were compared to those findings obtained in vivo

¹³C-methyl formate:observations of a sample of high-mass star-forming regions including Orion-KL and spectroscopic characterization

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