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Title: HIGH D{sub 2}O/HDO RATIO IN THE INNER REGIONS OF THE LOW-MASS PROTOSTAR NGC 1333 IRAS2A

Abstract

Water plays a crucial role both in the interstellar medium and on Earth. To constrain its formation mechanisms and its evolution through the star formation process, the determination of the water deuterium fractionation ratios is particularly suitable. Previous studies derived HDO/H{sub 2}O ratios in the warm inner regions of low-mass protostars. We here report a detection of the D{sub 2}O 1{sub 1,} {sub 0}-1{sub 0,} {sub 1} transition toward the low-mass protostar NGC 1333 IRAS2A with the Plateau de Bure interferometer: this represents the first interferometric detection of D{sub 2}O—and only the second solar-type protostar for which this isotopologue is detected. Using the observations of the HDO 5{sub 4,} {sub 2}-6{sub 3,} {sub 3} transition simultaneously detected and three other HDO lines previously observed, we show that the HDO line fluxes are well reproduced with a single excitation temperature of 218 ± 21 K and a source size of ∼0.''5. The D{sub 2}O/HDO ratio is ∼(1.2 ± 0.5) × 10{sup –2}, while the use of previous H{sub 2}{sup 18}O observations give an HDO/H{sub 2}O ratio of ∼(1.7 ± 0.8) × 10{sup –3}, i.e., a factor of seven lower than the D{sub 2}O/HDO ratio. These results contradict the predictions of current grain surface chemical models and indicatemore » that either the surface deuteration processes are poorly understood or that both sublimation of grain mantles and water formation at high temperatures (≳230 K) take place in the inner regions of this source. In the second scenario, the thermal desorption of the grain mantles would explain the high D{sub 2}O/HDO ratio, while water formation at high temperature would explain significant extra production of H{sub 2}O leading to a decrease of the HDO/H{sub 2}O ratio.« less

Authors:
;  [1]; ;  [2];  [3];  [4]
  1. Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen Ø (Denmark)
  2. Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands)
  3. Université de Toulouse, UPS-OMP, IRAP, F-31062 Toulouse (France)
  4. NASA Postdoctoral Program Fellow, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20770 (United States)
Publication Date:
OSTI Identifier:
22365236
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 792; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; DESORPTION; DEUTERATION; EXCITATION; FRACTIONATION; HEAVY WATER; INTERSTELLAR GRAINS; MASS; MOLECULES; PROTOSTARS; STAR EVOLUTION; STARS; SUBLIMATION

Citation Formats

Coutens, A., Jørgensen, J. K., Persson, M. V., Van Dishoeck, E. F., Vastel, C., and Taquet, V., E-mail: acoutens@nbi.dk. HIGH D{sub 2}O/HDO RATIO IN THE INNER REGIONS OF THE LOW-MASS PROTOSTAR NGC 1333 IRAS2A. United States: N. p., 2014. Web. doi:10.1088/2041-8205/792/1/L5.
Coutens, A., Jørgensen, J. K., Persson, M. V., Van Dishoeck, E. F., Vastel, C., & Taquet, V., E-mail: acoutens@nbi.dk. HIGH D{sub 2}O/HDO RATIO IN THE INNER REGIONS OF THE LOW-MASS PROTOSTAR NGC 1333 IRAS2A. United States. doi:10.1088/2041-8205/792/1/L5.
Coutens, A., Jørgensen, J. K., Persson, M. V., Van Dishoeck, E. F., Vastel, C., and Taquet, V., E-mail: acoutens@nbi.dk. Mon . "HIGH D{sub 2}O/HDO RATIO IN THE INNER REGIONS OF THE LOW-MASS PROTOSTAR NGC 1333 IRAS2A". United States. doi:10.1088/2041-8205/792/1/L5.
@article{osti_22365236,
title = {HIGH D{sub 2}O/HDO RATIO IN THE INNER REGIONS OF THE LOW-MASS PROTOSTAR NGC 1333 IRAS2A},
author = {Coutens, A. and Jørgensen, J. K. and Persson, M. V. and Van Dishoeck, E. F. and Vastel, C. and Taquet, V., E-mail: acoutens@nbi.dk},
abstractNote = {Water plays a crucial role both in the interstellar medium and on Earth. To constrain its formation mechanisms and its evolution through the star formation process, the determination of the water deuterium fractionation ratios is particularly suitable. Previous studies derived HDO/H{sub 2}O ratios in the warm inner regions of low-mass protostars. We here report a detection of the D{sub 2}O 1{sub 1,} {sub 0}-1{sub 0,} {sub 1} transition toward the low-mass protostar NGC 1333 IRAS2A with the Plateau de Bure interferometer: this represents the first interferometric detection of D{sub 2}O—and only the second solar-type protostar for which this isotopologue is detected. Using the observations of the HDO 5{sub 4,} {sub 2}-6{sub 3,} {sub 3} transition simultaneously detected and three other HDO lines previously observed, we show that the HDO line fluxes are well reproduced with a single excitation temperature of 218 ± 21 K and a source size of ∼0.''5. The D{sub 2}O/HDO ratio is ∼(1.2 ± 0.5) × 10{sup –2}, while the use of previous H{sub 2}{sup 18}O observations give an HDO/H{sub 2}O ratio of ∼(1.7 ± 0.8) × 10{sup –3}, i.e., a factor of seven lower than the D{sub 2}O/HDO ratio. These results contradict the predictions of current grain surface chemical models and indicate that either the surface deuteration processes are poorly understood or that both sublimation of grain mantles and water formation at high temperatures (≳230 K) take place in the inner regions of this source. In the second scenario, the thermal desorption of the grain mantles would explain the high D{sub 2}O/HDO ratio, while water formation at high temperature would explain significant extra production of H{sub 2}O leading to a decrease of the HDO/H{sub 2}O ratio.},
doi = {10.1088/2041-8205/792/1/L5},
journal = {Astrophysical Journal Letters},
number = 1,
volume = 792,
place = {United States},
year = {Mon Sep 01 00:00:00 EDT 2014},
month = {Mon Sep 01 00:00:00 EDT 2014}
}
  • The HDO/H{sub 2}O abundance ratio is thought to be a key diagnostic for the evolution of water during the star and planet formation process and thus for its origin on Earth. We here present millimeter-wavelength high angular resolution observations of the deeply embedded protostar NGC 1333-IRAS4B from the Submillimeter Array targeting the 3{sub 12}-2{sub 21} transition of HDO at 225.6 GHz (E{sub u} = 170 K). We do not (or only very tentatively) detect the HDO line toward the central protostar, contrasting the previous prominent detection of a line from another water isotopologue, H{sup 18}{sub 2}O, with similar excitation propertiesmore » using the IRAM Plateau de Bure Interferometer. The non-detection of the HDO line provides a direct, model-independent, upper limit to the HDO/H{sub 2}O abundance ratio of 6 x 10{sup -4} (3{sigma}) in the warm gas associated with the central protostar. This upper limit suggests that the HDO/H{sub 2}O abundance ratio is not significantly enhanced in the inner {approx}50 AU around the protostar relative to what is seen in comets and Earth's oceans and does not support previous suggestions of a generally enhanced HDO/H{sub 2}O ratio in these systems.« less
  • Evaporation of water ice above 100 K in the inner few 100 AU of low-mass embedded protostars (the so-called hot core) should produce quiescent water vapor abundances of {approx}10{sup -4} relative to H{sub 2}. Observational evidence so far points at abundances of only a few 10{sup -6}. However, these values are based on spherical models, which are known from interferometric studies to be inaccurate on the relevant spatial scales. Are hot cores really that much drier than expected, or are the low abundances an artifact of the inaccurate physical models? We present deep velocity-resolved Herschel-HIFI spectra of the 3{sub 12}-3{submore » 03} lines of H{sub 2}{sup 16}O and H{sub 2}{sup 18}O (1097 GHz, E{sub u}/k = 249 K) in the low-mass Class 0 protostar NGC 1333 IRAS2A. A spherical radiative transfer model with a power-law density profile is unable to reproduce both the HIFI data and existing interferometric data on the H{sub 2}{sup 18}O 3{sub 13}-2{sub 20} line (203 GHz, E{sub u}/k = 204 K). Instead, the HIFI spectra likely show optically thick emission from a hot core with a radius of about 100 AU. The mass of the hot core is estimated from the C{sup 18}O J = 9-8 and 10-9 lines. We derive a lower limit to the hot water abundance of 2 Multiplication-Sign 10{sup -5}, consistent with the theoretical predictions of {approx}10{sup -4}. The revised HDO/H{sub 2}O abundance ratio is 1 Multiplication-Sign 10{sup -3}, an order of magnitude lower than previously estimated.« less
  • A resonance Raman study of water has been performed by the use of excitation wavelengths ranging from 200 nm (6.20 eV) to 141 nm (8.78 eV). With excitation resonant with the dissociative A-italic-tilde state the spectra exhibit intensity exclusively in the symmetric stretching vibration, showing up to six quanta. There is no activity in the bending or antisymmetric stretching vibrations showing that the dissociation of the A-italic-tilde state of water proceeds initially along the symmetry stretch. Resonance with the second absorption band results in a spectrum exhibiting significant intensity in the bending vibration.