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The Water Deuteration as a Function of Radius in Massive Star-forming Region W33A with Herschel HIFI and the IRAM 30m Telescope

Hoogland, Hylke (2018) The Water Deuteration as a Function of Radius in Massive Star-forming Region W33A with Herschel HIFI and the IRAM 30m Telescope. Master's Thesis / Essay, Astronomy.

MSc Thesis Hylke Hoogland Water Deuteration W33A.pdf

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Context: Deuteration of water occurs most efficiently in cold (<30K) environments. By measuring the deuteration throughout the protostellar cloud, we can understand the conditions that are prevalent in the protostellar cloud. The deuteration as a function of radius for highmass protostellar sources has been studied only a few times. Aims: In my master thesis, I aim to determine the degree of water deuteration as a function of radius for the protostellar source W33A. This will give insight into how the water has formed in this source. Furthermore I aim to discover how the turbulent and in-fall velocities change throughout the cloud. Method: I use Herschel HIFI and IRAM 30m spectral data in the sub-millimeter and far infrared from 203 GHz to 1910 GHz. I will see which isotopologues of water are present in the data, derive abundances for these and derive a D/H value by means of radiative transfer modeling with the RADEX and RATRAN codes. Results: In total, 33 spectral features of water were found, though some uncertain: 7 H2O, 7 H218O, 9 HDO, 1 HD18O and 1 D2O lines. This is one of the first times that D2O was found in a high-mass protostellar source. Some lines show a P Cygni profile indicative of an expanding envelope. Radiative transfer modeling with RATRAN shows that a step function abundance profile reproduces the observations best, with the abundances [HDOin]=10^-6.5+/-1.0 , [HDOout]=10^-9+/-1.0, [H218Oin]=10^-6+/-1.0, [H218Oout]=10^-7.5+/-1.0 and therefore D/Hin=10^-3.7+/-1.0 and D/Hout=10^-4.5+/-1.0. The observations show little evidence of in-falling material. Conclusions: A high inner D/H ratio may be explained by a large amount of water sublimating from the dust grains as the protostar heats the surrounding material. The water may be formed in the pre-stellar phase. The cold conditions will have favoured a high D/H ratio in the water.

Item Type: Thesis (Master's Thesis / Essay)
Supervisor name: Tak, F.F.S. van der
Degree programme: Astronomy
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 13 Sep 2018
Last Modified: 02 Oct 2018 14:19

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