ALMA observations of water deuteration: A physical diagnostic of the formation of protostars

Abstract

The deuterium fractionation of water can serve as a tracer for the chemical and physical evolution of water during star formation and can constrain the origin of water in Solar System bodies. We determine the HDO/H${}_2$O ratio in the inner warm gas toward three low-mass Class 0 protostars selected to be in isolated cores, i.e., not associated with any cloud complexes. Previous sources for which the HDO/H${}_2$O ratio have been established were all part of larger star-forming complexes. Targeting these isolated protostars allows comparison of the water chemistry in isolated and clustered regions to determine the influence of local cloud environment. We present ALMA observations of the HDO $3_{1,2}$-$2_{2,1}$ and $2_{1,1}$-$2_{1,2}$ transitions at 225.897 GHz and 241.562 GHz along with the H${}_2^{18}$O $3_{1,3}$-$2_{2,0}$ transition at 203.407 GHz. The high angular resolution (0\farcs3-1\farcs3) allow the study of the inner warm envelope gas. Model-independent estimates for the HDO/H${}_2$O ratios are obtained and compared with previous determinations in the warm gas toward low-mass protostars. We detect the targeted water transitions toward the three sources with S/N > 5. We determine the HDO/H${}_2$O ratio toward L483, B335 and BHR71-IRS1 to be ($2.2\pm 0.4$)$\times 10^{-3}$, ($1.7\pm 0.3$)$\times 10^{-3}$, and ($1.8\pm 0.4$)$\times 10^{-3}$, respectively, assuming $T_{\mathrm{ex}}=124$ K. The degree of water deuteration of these isolated protostars are a factor of 2-4 higher relative to Class 0 protostars that are members of known nearby clustered star-forming regions. The results indicate that the water deuterium fractionation is influenced by the local cloud environment. This effect can be explained by variations in either collapse timescales or temperatures, which depends on local cloud dynamics and could provide a new method to decipher the history of young stars.

arXiv comment13 pages, 6 figures. Accepted for publication in A&A (18/09/2019)

References in corpus (41)

• The Birth Environment of the Solar System
• The Big Problems in Star Formation: the Star Formation Rate, Stellar Clustering, and the Initial Mass Function
• The ancient heritage of water ice in the solar system
• PROSAC: A Submillimeter Array Survey of Low-Mass Protostars. I. Overview of Program: Envelopes, Disks, Outflows and Hot Cores
• Tracing the Mass during Low-Mass Star Formation. I. Submillimeter Continuum Observations
• Water in star-forming regions with Herschel (WISH): II. Evolution of 557 GHz 110-101 emission in low-mass protostars
• Water in Star-Forming Regions with the Herschel Space Observatory (WISH): Overview of key program and first results
• The chemical history of molecules in circumstellar disks. I. Ices
• First detection of water vapor in a pre-stellar core
• Mapping ices in protostellar environments on 1000 AU scales: Methanol-rich ice in the envelope of Serpens SMM 4
• Tracing the Mass during Low-Mass Star Formation. III. Models of the Submillimeter Dust Continuum Emission from Class 0 Protostars
• A study of deuterated water in the low-mass protostar IRAS16293-2422
• Multilayer formation and evaporation of deuterated ices in prestellar and protostellar cores
• Herschel measurements of the D/H and 16O/18O ratios in water in the Oort-cloud comet C/2009 P1 (Garradd)
• Gaia-DR2 confirms VLBA parallaxes in Ophiuchus, Serpens and Aquila
• Probing the Early Stages of Low-Mass Star Formation in LDN 1689N: Dust and Water in IRAS 16293-2422A, B, and E
• Isotopic ratios of H, C, N, O, and S in comets C/2012 F6 (Lemmon) and C/2014 Q2 (Lovejoy)
• Terrestrial deuterium-to-hydrogen ratio in water in hyperactive comets
• L483: Warm Carbon-Chain Chemistry Source Harboring Hot Corino Activity
• Cometary ices in forming protoplanetary disc midplanes
• Discovery of a Hot Corino in the Bok Globule B335
• Water ice deuteration: a tracer of the chemical history of protostars
• A Herschel Study of D/H in Water in the Jupiter-Family Comet 45P/Honda-Mrkos-Pajdusakova and Prospects for D/H Measurements with CCAT
• Detection of Infall in the Protostar B335 with ALMA
• Reconstructing the history of water ice formation from HDO/H2O and D2O/HDO ratios in protostellar cores
• The deuterium fractionation of water on solar-system scales in deeply-embedded low-mass protostars
• HDO abundance in the envelope of the solar-type protostar IRAS16293-2422
• Subarcsecond resolution observations of warm water towards three deeply embedded low-mass protostars
• The 16OH/18OH and OD/OH isotope ratios in comet C/2002 T7 (LINEAR)
• The organic chemistry in the innermost, infalling envelope of the Class 0 protostar L483
• Interstellar ices as witnesses of star formation: selective deuteration of water and organic molecules unveiled
• Water delivery from cores to disks: deuteration as a probe of the prestellar inheritance of H2O
• Sensitive Limits on the Water Abundance in Cold Low Mass Molecular Cores
• Deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B
• The HDO/H2O ratio in gas in the inner regions of a low-mass protostar
• High D${}_2$O/HDO ratio in the inner regions of the low-mass protostar NGC1333 IRAS2A
• Hot water in the inner 100 AU of the Class 0 protostar NGC1333 IRAS2A
• The Formation Conditions of the Wide Binary Class 0 Protostars within BHR 71
• Water deuterium fractionation in the inner regions of two solar type protostars
• The Class 0 Protostar BHR71: Herschel Observations and Dust Continuum Models
• The shocked gas of the BHR71 outflow observed by Herschel: indirect evidence for an atomic jet

Cited by in corpus (25)

• Astrochemistry During the Formation of Stars
• Water in star-forming regions (WISH): Physics and chemistry from clouds to disks as probed by Herschel spectroscopy
• High D/H ratios in water and alkanes in comet 67P/Churyumov-Gerasimenko measured with the Rosetta/ROSINA DFMS
• Carbon-Chain Chemistry in the Interstellar Medium
• ALMA observations of doubly deuterated water: Inheritance of water from the prestellar environment
• JWST Observations of Young protoStars (JOYS): overview of program and early results
• X-ray induced chemistry of water and related molecules in low-mass protostellar envelopes
• Successive deuteration in low-mass star-forming regions: the case of D${}_2$-methanol (CHD${}_2$OH) in IRAS 16293-2422
• JWST detections of amorphous and crystalline HDO ice toward massive protostars
• Methanol deuteration in high-mass protostars
• Modeling chemistry during star formation: Water deuteration in dynamic star-forming regions
• Different degrees of nitrogen and carbon depletion in the warm molecular layers of protoplanetary disks
• A 3D physico-chemical model of a pre-stellar core. I. Environmental and structural impact on the distribution of CH${}_3$OH and $c$-C${}_3$H${}_2$
• A high HDO/H${}_2$O ratio in the Class I protostar L1551 IRS5
• Millimetre and sub-millimetre spectroscopy of doubly deuterated acetaldehyde (CHD2CHO) and first detection towards IRAS 16293-2422
• ALMA ACA study of the H${}_2$S/OCS ratio in low-mass protostars
• HDO ice detected toward an isolated low-mass protostar with JWST
• Was Earth's water acquired locally during the earliest phases of the Solar System formation?
• Pristine ices in a planet-forming disk revealed by heavy water
• The first interferometric measurements of NH${}_2$D/NH${}_3$ ratio in hot corinos
• Chemical compositions in the vicinity of protostars in Ophiuchus
• Gas phase Elemental abundances in Molecular cloudS (GEMS). IX. Deuterated compounds of H2S in starless cores
• Looking for evidence of high-mass star formation at core scale in a massive molecular clump
• CHemical Evolution in MassIve star-forming COres (CHEMICO). I. Evolution of the temperature structure
• Clump-scale chemistry in the NGC2264-D cluster-forming region