The HDO/H2O and D2O/HDO ratios in solar-type protostars

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1 The HD/H and D/HD ratios in solar-type protostars Audrey CUTENS University College London M. V. Persson, J. K. Jørgensen, E. F. van Dishoeck, C. Vastel, V. Taquet, S. Bottinelli, E. Caux, D. Harsono, J. M. Lykke

2 Deuterium fractionation High deuterium fractionation observed in low-mass protostars Main chemical reactions extracting D from HD (main D reservoir in dense regions): H + + HD D E CH + + HD CD E 4 Energy H + + D + D H D + separation ~ 55 K ~ 6 K ~ 64 K C H + + HD C HD E 5 Cold regions (- K) : backwards reactions not efficient despite the high abundance Subsequent reactions will deuterate more and more molecules. Atomic D/H ratio increases in the gas phase and consequently the deuterium fractionation of molecules formed on the grain surfaces increases Deuterium fractionation sensitive to formation conditions (T, n)

3 Water deuterium fractionation Ion Molecule High-T E A [K] ~ + H + ~ ~ H + + H + e - e - H H H Surface s- s- s- H,, H H + HC + e - T s- Gas Phase Grain Surface van Dishoeck et al. PPVI

4 Water deuterium fractionation Ion Molecule High-T E A [K] ~ + H + ~ ~ High water D/H ratios H + + H + e - e - H H H Surface s- s- s- H,, H High water D/H ratios H + HC + e - T s- Gas Phase 4 Grain Surface van Dishoeck et al. PPVI

5 Water deuterium fractionation Ion Molecule High-T E A [K] ~ + H + ~ ~ H + + H + e - e - H H H Surface s- s- s- H,, H Low water D/H ratios H + HC + e - T s- Gas Phase 5 Grain Surface van Dishoeck et al. PPVI

6 rigin of terrestrial water Delivery of water on Earth by comets and/or asteroids through impacts Where does the water contained in comets and asteroids come from? How and when did this water form? Altwegg et al. 5 Spitzer Science Center IR Compendium 6

7 Detection of water in the inner regions of solar-type protostars First spatially and spectrally resolved image of water vapor around a Class protostar (NGC IRAS 4B) through millimeter wavelength observations of the H 8 isotopologue with the PdBI (Jørgensen & van Dishoeck ) Jørgensen & van Dishoeck () Compact emission consistent with thermal desorption of the icy grain mantles in the warm inner region of the protostar (T > K) 7

8 HD in the inner regions of solar-type protostars H 8,, HD,, HD detected in the warm inner regions of Class protostars (Codella et al., Persson et al., 4, Taquet et al., Coutens et al. 4) with interferometers 4 5 AU 4 IRAS A AU Compact emission as seen for 8 Dec o set [ ] IRAS 4A-NW Assuming 6 / 8 ~ 5 (Solar System value) 4 AU 4 AU 4 4 LTE modeling used to derive the HD/ ratio AU IRAS 4B AU RA o set [ ] 8 Persson et al. (4)

9 The HD/ ratios in the inner regions of solar-type protostars Comets Protostars Rosetta Earth s oceans Cosmic D/H Persson et al. (4) 9

10 The HD/ ratios in the inner regions of solar-type protostars Rosetta Comets Protostars What about the D /HD ratios? Earth s oceans Cosmic D/H Persson et al. (4)

11 Detection of D in the inner region of a solar-type protostar First interferometric detection of D towards the Class protostar NGC IRASA with the PdBI (Coutens et al. 4) LTE modeling (HD, D, 8 ) D /HD ~. - HD/ ~.7 - D /HD ~ 7 HD/ Expectations : Statistically D /HD ~ /4 HD/ Surface grain chemical models also predicted D /HD HD/ Coutens et al. (4, ApJL)

12 Is D /HD > HD/ common in low-mass protostars? ALMA program accepted to study water deuteration in the low-mass protostar IRAS 69-4 (binary source, A and B) Partly observed observations of several HD, D and 8 transitions Resolution of. (~5 AU): possible to study the dynamics with spatially resolved lines

13 How to explain D /HD > HD/ in the inner region of a solar-type protostar? Natural consequence of the evolution in the early cold stages of low-mass star formation (Furuya et al. 6) Time Molecular cloud Stage I -dominated (layer I) dust f D < f D < - Furuya et al. 6 Prestellar core Stage II C & CH H-rich (layer II) -dominated (layer I) dust f D < f D < - - << f D < f D Fractional composition, D/H Cloud Core C C CH H D / HD/ Num. of the total ice layers 4

14 How to explain D /HD > HD/ in the inner region of a solar-type protostar Natural consequence of the evolution in the early cold stages of low-mass star formation (Furuya et al. 6) Time Molecular cloud Stage I -dominated (layer I) dust f D < f D < - Furuya et al. 6 Prestellar core Stage II C & CH H-rich (layer II) -dominated (layer I) dust f D < f D < - - << f D < f D 5 Abundance ratio Abundance [n H ] log (n H [cm - ]) HD D D /HD HD/ Temperature [K] 5 PR( ) Radius [AU]

15 Water deuterium fractionation in the cold outer regions of protostars. HD, -, GHz.5 HD, -, GHz T mb (K).6 T mb (K) v LSR (km s - ) v LSR (km s - ) Deep absorptions for the fundamental HD lines at 894 GHz and 465 GHz detected with Herschel/HIFI and the JCMT/APEX observed towards low-mass protostars fundamental D lines detected in absorption towards IRAS 69-4 with Herschel/HIFI (Vastel et al., Coutens et al. ) and the JCMT (Butner et al. 7) Probe of the cold regions 6 Coutens et al. ()

16 Water deuterium fractionation in the cold outer regions of protostars Spherical non-lte modeling of the HD lines Abundance Presence of a water rich layer surrounding the low-mass protostars (Coutens et al., ) Probably formed by photodesorption by the external/cosmic ray induced UV field or chemical desorption hot corino Cold envelope High HD/ ratio ~ 5% and D /HD ~ % for the outermost regions of the protostar IRAS 69 ~ Radius Decrease of the water D/H ratio from the cold outer regions to the warm inner regions In agreement with chemical models including layered structure of the icy grain mantles (Taquet et al. 4, Furuya et al. 6) 7

17 Summary Water deuteration helpful to constrain the water formation mechanisms in the interstellar medium and to follow the evolution of water during the star formation process Combination of the D /HD and HD/ ratios is a useful tool to reveal the past history of water formation Inner HD/ ratios consistent in some cases with cometary values Inner regions of the protostar NGC IRASA : D /HD > HD/ Decrease of the water deuterium fractionation from the cold outer regions to the warm inner regions Result of the evolution of water formation during the early cold stages of low-mass star formation (molecular cloud + prestellar core, Furuya et al. 6) 8

18 Future Measurements of the HD/ ratios at different stages (Class I, Class II) would help us to understand the evolution of water during the star formation process. Prestellar core Spitzer Science Center IR Compendium See poster P7 on the detectability of deuterated water in prestellar cores (Quénard et al. 6) Class protostar? Comets 9