Bérengère Parise

Testing grain surface chemistry models using deuterated probes in low-mass star-forming regions.

Bonn, Germany

2Bérengère Parise - Max Planck Institut für Radioastronomie

Introduction

For 30 years, observations in the ISM have shown fractionations XD/XH [D]/[H] (~1.5 10-5)

D2CO/H2CO ~ 0.05 towards the

low-mass protostar IRAS16293 (Ceccarelli et al. 1998, A&A 338, L43)

(figure : M.R. Hogerheijde in van Dishoeck & Blake 1998)

D2CO/H2CO ~ 0.003 in Orion(Turner, 1990, ApJ 362, L29) Active grain chemistry

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Chemical processes

Gas phase reactions ?

Grain surface reactions ?

(e.g. Roberts & Millar 2000, A&A 361, 398)

(e.g. Tielens 1983, A&A 119, 177)

Desorption

Prestellar core phase Envelope heated by the protostar

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Tielens & Hagen, 1982, A&A 114, 245Tielens, 1983, A&A 119, 177

Fractionation due to : • enhanced atomic D/H ratio in the gas phase (D formed from H2D+)

requires CO depletion and low temperature • lower activation barriers for reactions involving D

CO

H2CO

Roberts & Millar 2000, A&A 361, 398Roberts & Millar 2000, A&A 364, 780

H3+ + HD H2D+ + H2

root reaction :

H2D+ propagates the deuterium to other molecules

Adsorption in grain mantles

Required physicalconditions

low temperatureCO depletion

Gas phase versus grain chemistry

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Charnley et al. 1997, AJ 482, L203

A test for surface chemistry ?

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Deuterated methanol in IRAS16293Parise et al. 2002, A&A 393, L49Parise et al. 2004, A&A, 416, 159

IRAM 30m observations IRAM 30m observations

23 CH23 CH22DOH lines DOH lines

6 CH6 CH33OD lines OD lines

15 CHD15 CHD22OH linesOH lines

12 CD12 CD33OH lines OH lines

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+38f(CH2DOH) = 37 % -19

+2.2f(CH3OD) = 1.8 % -1.2

+8.4f(CHD2OH) = 7.4 % -4.4

+1.0f(CD3OH) = 1.0 % -0.6

IRAS 16293-2422+3+3

-2-2

-4-4

-4-4

Population diagrams

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requires an atomic D/H ratio ~ 0.1-0.2 in the gas phase. This atomic fractionation is now reproduced by new generation models including D2H+ and D3

+ (e.g. Roberts et al. 2003) See poster by Vastel et al.

CH2DOH/CH3OD very high compared with the statistical ratio 3 CH3OD destroyed in the gas phase by protonation ?

CH3ODH+ CH3OH + D + e-

CH3OD + H + e-

confirmed by Osamura et al. 2004

dashed lines : surface chemistry model Stantcheva et al. 2003, MNRAS 340, 983

red : IRAS16293-2422 observations

Comparison to grain chemistry models

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challenged by Dartois et al. (on the edge of one SWS detector)VLT observation on W33A :

HDO / H2O < 10-2 (Dartois et al. 2003, A&A 399, 1009)

Inconclusive mostly because high-mass protostars show a lowerInconclusive mostly because high-mass protostars show a lowerdegree of deuteration than low-mass protostars ? degree of deuteration than low-mass protostars ?

Grain surface model predictions : HDO / H2O ~ 20 %

What about looking directly on the grains ?

Observations in solid phase are less sensitive than gas phase observations. H2O : main constituent of icy mantles around dust grains.

Search for HDO in the ices

Previous attempts :

Detection of HDO in high mass protostars W33A et NGC7538 IRS9 (Teixeira et al., 1999, A&A, L19-L22)

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Recherche de HDO en phase solide sur les grains

Observation of OD and OH stretch bands (in absorption) at 4.1 and 3 m

with SpeX on IRTF (Mauna Kea) R = 1500

CH3 D:O2 -1:1 ice before and after UV irradiation (Dartois et al 2000)

Search for solid HDO in low-mass protostars grain mantles

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Parise et al. 2003, A&A 410, 897

4 class I protostars• bright in NIR• high J-K extinction• D2CO/H2CO ~ 5%

Solid phase HDO/H2O (1)

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Solid phase HDO/H2O (2)

HDO/H2O ≤ ~ 1%

Does this exclude grain surface chemistry for deuteration ?Or has water a different fractionation than methanol ?

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Deuterated water in the gas phaseIRAS 16293 - Observations

JCMT

IRAM

Frequency (GHz)

Eup

(K)

80.6 46.8

225.9 167.7

241.6 95.3

266.2 157.3

464.9 22.3

JCMT and IRAM observations ON-source & outflow 5 lines detected on-source no emission detected towards the outflow.

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Deuterated water in IRAS 16293 - Modelling

Tev = 100 K

R

xin

xout

inner envelope : HDO/H2O = 3%outer envelope : HDO/H2O < 0.2 %

Model of envelope emission from

Ceccarelli, Hollenbach & Tielens 1996: density structure : inside-out collapse

(Shu scenario).gas temperature computed

self-consistently : cooling depends on

CO, O and H2O abundance.

Adapted to HDO study : collision coefficients from Green (1989)use of the density and temperature

profiles as well as water abundance

derived by Ceccarelli et al. (2000).HDO abundance :

Parise et al. 2005, A&A 431, 547

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Deuterated methanol observations :

IRAS16293-2422 CH2DOH/CH3OH = 37 % CH3OD/CH3OH = 1.8 % CHD2OH/CH3OH = 7.4 % CD3OH/CH3OH = 1.0 %

Consistent with grain chemistry models, but : these models require a high atomic D/H ratio in the gas phase, which can only occur when CO is heavily depleted. these models predict HDO/H2O ~ 20 % ...

... HDO observation in grain mantles :

NGC1333 SVS12, SVS13, L1489 IRS, TMR1 HDO/H2O ≤ 1 %

... HDO observation in the gas phase :

IRAS16293-2422 HDO/H2O = 3% in the inner enveloppe HDO/H2O < 0.2 % in the outer enveloppe.

Questions raised by single dish observations

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Conclusions

Modelling of the single-dish HDO emission points to a fractionation enhancement of water in the inner warm envelope (“hot corino”).

Same for methanol ?Unfortunately such a modelling cannot be performed for CH2DOH because collision coefficients are not available.

Moreover interferometric observations have shown that IRAS16293 is a binary with different chemical properties (PdBI, Bottinelli et al. 2004; SMA, Kuan et al. 2004, see poster by Huang et al).

Accurate comparison to grain surface models can therefore only be done after observing the spatial distribution of deuterated methanol.

Special thanks to the organizers of this conference.

Thanks to my collaborators :Cecilia Ceccarelli - Emmanuel Caux

Eric Herbst - A.G.G.M. TielensAlain Castets - Bertrand Lefloch

And all the WAGOS groupTed Simon - John Rayner

Indra MukhopadhyayEmmanuel Dartois - Laurent Loinard

Peter Schilke - Karl Menten

Operations at IRAM are funded by the CNRS (Centre National de la Recherche Scientifique, France), the MPG (Max Planck Gesellschaft, Germany), and the IGN (Instituto Geografico Nacional, Spain).

The Infrared Telescope Facility is operated by the University of Hawaii under Cooperative Agreement no. NCC 5-538 with the National Aeronautics and Space Administration, Office of Space Science, Planetary Astronomy Program.

The James Clerk Maxwell Telescope (JCMT) is operated by the Joint Astronomy Centre on behalf of the UK Particle Physics and Astronomy Research Council (PPARC), the National Research Council of Canada and the Netherlands Organisation for Pure Research.

No animal was hurt during the preparation of this talk