Water deuterium fractionation in star-formation regions
Speaker: Dr. Liu, Fang-Chun 劉芳君
National Taiwan Normal University
Time: 15:30pm 15th June, 2018 (Friday)
Venue: R521, IoA, 2nd General Building 綜二館R521
Water is an essential molecule to oxygen chemistry and to the proliferation of life. Also, it is the main constituent of icy grain mantles in the Universe. The formation of water can be studied through the HDO/H2O ratio. Thanks to the launch of the Herschel Space Observatory and the advance of sensitive sub millimeter receivers on ground-based telescopes, many H2O and HDO transitions can now be observed, enabling more accurate studies of the level of water fractionation, i.e., the enhancement of the HDO/H2O abundance ratio over the D/H elemental ratio. Using these new technologies, we aim at revisiting the water fractionation studies toward star-forming regions. We present here detailed studies of the D/H ratios of water in one low-mass protostar and six luminous high-mass star-forming regions. Deuterated water and H2-18O has been detected in these sources with APEX, SMA and Herschel Space Observatory. We analyzed these observations using the 1-D radiative transfer code RATRAN to obtain the HDO and H2-18O fractional abundances throughout the envelopes. The results show that the HDO fractional abundances in the inner and outer regions are different by more than two orders, which implies that the sublimation is very similar in low- and high-mass star-forming regions. Previous and our studies show that the values of the HDO fractional abundance in star-forming regions with different masses do not correlate with their evolution. The H2O abundance is deduced from the analysis of the H2-18O transition lines. The similarity of the measured HDO/H2O ratios suggests that the chemical evolution of water is the same regardless of the masses of the regions.