Detectability of deuterated water in prestellar cores

Abstract

Water is an important molecule in the chemical and thermal balance of dense molecular gas, but knowing its history through-out the various stages of the star formation is a fundamental problem. Its molecular deuteration provides us with a crucial clue to its formation history. H${}_2$O has recently been detected for the first time towards the prestellar core L1544 with the Herschel Space Observatory with a high spectral resolution (HIFI instrument). Prestellar cores provide the original reservoir of material from which future planetary systems are built, but few observational constraints exist on the formation of water and none on its deuteration before the collapse starts and a protostar forms at the centre. We report on new APEX observations of the ground state 1${}_{0,1}$-0${}_{0,0}$ HDO transition at 464 GHz towards the prestellar core L1544. The line is undetected, and we present an extensive study of the conditions for its detectability in cold and dense cloud cores. The water and deuterated water abundances have been estimated using an advanced chemical model simplified for the limited number of reactions or processes that are active in cold regions (< 15 K). We use the LIME radiative transfer code to compute the expected intensity and profile of both H${}_2$O and HDO lines and compare them with the observations. We present several ad hoc profiles that best-fit the observations and compare the profiles with results from an astrochemical modelling, coupling gas phase and grain surface chemistry. Our comparison between observations, radiative transfer, and chemical modelling shows the limits of detectability for singly deuterated water, through the ground-state transitions 1${}_{0,1}$-0${}_{0,0}$ and 1${}_{1,1}$-0${}_{0,0}$ at 464.9 and 893.6 GHz, respectively, with both single-dish telescope and interferometric observations.

8 pages, 6 figures

References in corpus (12)

• Observations of the Icy Universe
• Observing the gas temperature drop in the high-density nucleus of L 1544
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• Deuterated methanol in the pre-stellar core L1544
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• Chemical modeling of water deuteration in IRAS16293-2422
• Water deuterium fractionation in the high-mass star-forming region G34.26+0.15 based on Herschel/HIFI data

Cited by in corpus (6)

• Seeds Of Life In Space (SOLIS): The organic composition diversity at 300--1000 au scale in Solar-type star forming regions
• Sulphur chemistry in the L1544 pre-stellar core
• Chemical modelling of complex organic molecules with peptide-like bonds in star-forming regions
• Why does ammonia not freeze out in the center of pre-stellar cores?
• Detection of the HC${}_3$NH${}^{+}$ and HCNH${}^{+}$ ions in the L1544 pre-stellar core
• Abundance of HOCO+ and CO2 in the outer layers of the L1544 prestellar core