TY - BOOK

T1 - The Complex Chemistry of Embedded Protostars

AU - Lykke, Julie Maria

PY - 2015

Y1 - 2015

N2 - Stars are born in interstellar space within denseregions of large clouds of dust and gas. In its earliest stages, the emissionfrom the young star itself is obscured from us, since the dust absorb thevisible light emitted by the star. But with radio observations of wavelength inthe millimeter and sub-millimeter regime, it is possible to detect theso-called protostars, because of the effect of their presence on thesurroundings. Protostars emit an enormous amount of heat, which will increasethe temperature of the nearby dust and gas. Molecules can form both on the icysurfaces of dust grains and in the gas phase. Far away from the protostar,where the temperature is low, molecules will be frozen into the ice layer thatcovers the dust grains, while close to the protostars, where the temperature ishigh, the ice and the molecules will evaporate off the grains. The field ofastrochemistry - or molecular astrophysics - has evolved fast in recent years,due to major technological advancements for radio telescopes. But some of themost central questions still remain unanswered: how, where and when are complexorganic molecules formed around young stars? How complex can these moleculesbecome? Is there a difference in the chemistry for high- and low-massprotostars? The work in this thesis aim to provide answer for these questions by searchingfor molecules where they have not been detected before and by comparing therelative abundance of different molecules to models and laboratory work as wellas between different sources. The analysis is based on observations of twohigh-mass sources, W51/e2 and G34.3+0.2, with the IRAM 30 m single dishtelescope, and of a low-mass protostar, IRAS16293-2422, with the Atacama Large Millimeter/submillimeterArray. We have successfully made a number of new detections: a tentativedetection of ethylene glycol for the first time in G34.3+0.2, while confirmingthe previous marginal detection of ethylene glycol in W51/e2. For the first timetoward a low-mass protostar, we have made firm detections of acetone, propanaland ethylene oxide in IRAS16293-2422. For some relative abundance ratios, wefind that these are seemingly correlated to the source luminosity, thus we seea difference between high- and low-mass protostars. But for other ratios wefind no significant difference between them. Chemical models and laboratorystudies fail to reproduce the observed range of high- and low-mass sources.Modified models and laboratory work as well as more observations are thereforeneeded to further develop our understanding of the chemistry occurring instar-forming regions.

AB - Stars are born in interstellar space within denseregions of large clouds of dust and gas. In its earliest stages, the emissionfrom the young star itself is obscured from us, since the dust absorb thevisible light emitted by the star. But with radio observations of wavelength inthe millimeter and sub-millimeter regime, it is possible to detect theso-called protostars, because of the effect of their presence on thesurroundings. Protostars emit an enormous amount of heat, which will increasethe temperature of the nearby dust and gas. Molecules can form both on the icysurfaces of dust grains and in the gas phase. Far away from the protostar,where the temperature is low, molecules will be frozen into the ice layer thatcovers the dust grains, while close to the protostars, where the temperature ishigh, the ice and the molecules will evaporate off the grains. The field ofastrochemistry - or molecular astrophysics - has evolved fast in recent years,due to major technological advancements for radio telescopes. But some of themost central questions still remain unanswered: how, where and when are complexorganic molecules formed around young stars? How complex can these moleculesbecome? Is there a difference in the chemistry for high- and low-massprotostars? The work in this thesis aim to provide answer for these questions by searchingfor molecules where they have not been detected before and by comparing therelative abundance of different molecules to models and laboratory work as wellas between different sources. The analysis is based on observations of twohigh-mass sources, W51/e2 and G34.3+0.2, with the IRAM 30 m single dishtelescope, and of a low-mass protostar, IRAS16293-2422, with the Atacama Large Millimeter/submillimeterArray. We have successfully made a number of new detections: a tentativedetection of ethylene glycol for the first time in G34.3+0.2, while confirmingthe previous marginal detection of ethylene glycol in W51/e2. For the first timetoward a low-mass protostar, we have made firm detections of acetone, propanaland ethylene oxide in IRAS16293-2422. For some relative abundance ratios, wefind that these are seemingly correlated to the source luminosity, thus we seea difference between high- and low-mass protostars. But for other ratios wefind no significant difference between them. Chemical models and laboratorystudies fail to reproduce the observed range of high- and low-mass sources.Modified models and laboratory work as well as more observations are thereforeneeded to further develop our understanding of the chemistry occurring instar-forming regions.

UR - https://soeg.kb.dk/permalink/45KBDK_KGL/fbp0ps/alma99122253478605763

M3 - Ph.D. thesis

BT - The Complex Chemistry of Embedded Protostars

PB - The Niels Bohr Institute, Faculty of Science, University of Copenhagen

ER -