Heavy water around the L1448-mm protostar

Codella, C.; Ceccarelli, C.; Nisini, B.; Bachiller, R.; Cernicharo, J.; Gueth, F.; Fuente, A.; Leflóch, B.

doi:10.1051/0004-6361/201015240

Cited by 62 publications

(82 citation statements)

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“…For IRAS 16293-2422, IRAS 4A, and IRAS 4B, the HDO fundamental 1 1,1 -0 0,0 transition was observed at high sensitivity with Herschel/HIFI, allowing us to strongly constrain the outer abundance of deuterated water. The estimate of the HDO inner abundance in L1448-mm by Codella et al (2010) is based on interferometric observations of the HDO 1 1,0 -1 1,1 line at 80.6 GHz. Using the spherical source structure determined by Jørgensen et al (2002), the abundance is then estimated at 4 × 10 −7 .…”

Section: Discussionmentioning

confidence: 99%

Deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B

Coutens

Vastel

Cabrit

et al. 2013

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Context. The measure of the water deuterium fractionation is a relevant tool for understanding mechanisms of water formation and evolution from the prestellar phase to the formation of planets and comets. Aims. The aim of this paper is to study deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B, to compare their HDO abundance distributions with other star-forming regions, and to constrain their HDO/H 2 O abundance ratios. Methods. Using the Herschel/HIFI instrument as well as ground-based telescopes, we observed several HDO lines covering a large excitation range (E up /k = 22-168 K) towards these protostars and an outflow position. Non-local thermal equilibrium radiative transfer codes were then used to determine the HDO abundance profiles in these sources. Results. The HDO fundamental line profiles show a very broad component, tracing the molecular outflows, in addition to a narrower emission component and a narrow absorbing component. In the protostellar envelope of NGC 1333 IRAS 4A, the HDO inner (T ≥ 100 K) and outer (T < 100 K) abundances with respect to H 2 are estimated with a 3σ uncertainty at 7.5 +3.5 −3.0 × 10 −9 and 1.2 +0.4 −0.4 × 10 −11 , respectively, whereas in NGC 1333 IRAS 4B they are 1 +1.8 −0.9 × 10 −8 and 1.2 +0.6 −0.4 × 10 −10 , respectively. Similarly to the low-mass protostar IRAS 16293-2422, an absorbing outer layer with an enhanced abundance of deuterated water is required to reproduce the absorbing components seen in the fundamental lines at 465 and 894 GHz in both sources. This water-rich layer is probably extended enough to encompass the two sources, as well as parts of the outflows. In the outflows emanating from NGC 1333 IRAS 4A, the HDO column density is estimated at about (2-4) × 10 13 cm −2 , leading to an abundance of about (0.7-1.9) × 10 −9 . An HDO/H 2 O ratio between 7 × 10 −4 and 9 × 10 −2 is also derived in the outflows. In the warm inner regions of these two sources, we estimate the HDO/H 2 O ratios at about 1 × 10 −4 -4 × 10 −3 . This ratio seems higher (a few %) in the cold envelope of IRAS 4A, whose possible origin is discussed in relation to formation processes of HDO and H 2 O. Conclusions. In low-mass protostars, the HDO outer abundances range in a small interval, between ∼10 −11 and a few 10 −10 . No clear trends are found between the HDO abundance and various source parameters (L bol , L smm , L smm /L bol , T bol , L 0.6 bol /M env ). A tentative correlation is observed, however, between the ratio of the inner and outer abundances with the submillimeter luminosity.

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Section: Discussionmentioning

confidence: 99%

Deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B

Coutens

Vastel

Cabrit

et al. 2013

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“…Velocity-resolved spectra of 12 CO up to J u = 10 (Yıldız et al 2010(Yıldız et al , 2012Bjerkeli et al 2011;Benedettini et al 2012) and of several H 2 O Codella et al 2010;Kristensen et al 2011Kristensen et al , 2012Santangelo et al 2012;Vasta et al 2012) and OH (Wampfler et al 2011) lines indicate that the bulk of the far-infrared emission has broad line wings with Δ > 15 km s −1 . The quiescent warm inner envelope is primarily seen in the narrow (Δ 5 km s −1 ) 13 CO and C 18 O isotopolog mid-J spectra centered at the source position but this component does not contribute to H 2 O emission.…”

Section: Origin Of Far-ir Line Emissionmentioning

confidence: 99%

Water in star-forming regions withHerschel(WISH)

Karska

Herczeg

Dishoeck

et al. 2013

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Context. Understanding the physical phenomena involved in the earlierst stages of protostellar evolution requires knowledge of the heating and cooling processes that occur in the surroundings of a young stellar object. Spatially resolved information from its constituent gas and dust provides the necessary constraints to distinguish between different theories of accretion energy dissipation into the envelope. Aims. Our aims are to quantify the far-infrared line emission from low-mass protostars and the contribution of different atomic and molecular species to the gas cooling budget, to determine the spatial extent of the emission, and to investigate the underlying excitation conditions. Analysis of the line cooling will help us characterize the evolution of the relevant physical processes as the protostar ages. Methods. Far-infrared Herschel-PACS spectra of 18 low-mass protostars of various luminosities and evolutionary stages are studied in the context of the WISH key program. For most targets, the spectra include many wavelength intervals selected to cover specific CO, H 2 O, OH, and atomic lines. For four targets the spectra span the entire 55-200 μm region. The PACS field-of-view covers ∼47 with the resolution of 9.4 . Results. Most of the protostars in our sample show strong atomic and molecular far-infrared emission. Water is detected in 17 out of 18 objects (except TMC1A), including 5 Class I sources. The high-excitation H 2 O 8 18 -7 07 63.3 μm line (E u /k B = 1071 K) is detected in 7 sources. CO transitions from J = 14−13 up to J = 49−48 are found and show two distinct temperature components on Boltzmann diagrams with rotational temperatures of ∼350 K and ∼700 K. H 2 O has typical excitation temperatures of ∼150 K. Emission from both Class 0 and I sources is usually spatially extended along the outflow direction but with a pattern that depends on the species and the transition. In the extended sources, emission is stronger off source and extended on ≥10 000 AU scales; in the compact sample, more than half of the flux originates within 1000 AU of the protostar. The Conclusions. The PACS data probe at least two physical components. The H 2 O and CO emission very likely arises in non-dissociative (irradiated) shocks along the outflow walls with a range of pre-shock densities. Some OH is also associated with this component, most likely resulting from H 2 O photodissociation. UV-heated gas contributes only a minor fraction to the CO emission observed by PACS, based on the strong correlation between the shock-dominated CO 24-23 line and the CO 14-13 line. [O i] and some of the OH emission probe dissociative shocks in the inner envelope. The total far-infrared cooling is dominated by H 2 O and CO, with the fraction contributed by [O i] increasing for Class I sources. Consistent with previous studies, the ratio of total far-infrared line emission over bolometric luminosity decreases with the evolutionary state.

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“…Interestingly, L1157-B1 also shows emission in molecular ions, such as HCO + , HCS + , and N 2 H + (Bachiller & Perez Gutierrez 1997;Codella et al 2010Codella et al , 2013Yamaguchi et al 2012), making it a unique target for investigating the chemistry of molecular ions in protostellar shocks.…”

Section: Previous Work On L1157mentioning

confidence: 99%

Molecular ions in the protostellar shock L1157-B1

Podio

Leflóch

Ceccarelli

et al. 2014

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Aims. We perform a complete census of molecular ions with an abundance greater than ∼10 −10 in the protostellar shock L1157-B1. This allows us to study the ionisation structure and chemistry of the shock.Methods. An unbiased high-sensitivity survey of L1157-B1 performed with the IRAM-30 m and Herschel/HIFI as part of the CHESS and ASAI large programmes allows searching for molecular ions emission. Then, by means of a radiative transfer code in the large velocity gradient approximation, the gas physical conditions and fractional abundances of molecular ions are derived. The latter are compared with estimates of steady-state abundances in the cloud and their evolution in the shock calculated with the chemical model Astrochem.Results. We detect emission from HCO + , H 13 CO + , N 2 H + , HCS + , and for the first time in a shock, from HOCO + and SO + . The bulk of the emission peaks at blue-shifted velocity, ∼0.5-3 km s −1 with respect to systemic, has a width of ∼3-7 km s −1 and is associated with the outflow cavities (T kin ∼ 20−70 K, n H 2 ∼ 10 5 cm −3 ). A high-velocity component up to −40 km s −1 , associated with the primary jet, is detected in the HCO + 1-0 line. Observed HCO + and N 2 H + abundances (X HCO + ∼ 0.7−3 × 10 −8 , X N 2 H + ∼ 0.4−8 × 10 −9 ) agree with steady-state abundances in the cloud and with their evolution in the compressed and heated gas in the shock for cosmic rays ionisation rate ζ = 3 × 10 −16 s −1 . HOCO + , SO + , and HCS + observed abundances (X HOCO + ∼ 10 −9 , X SO + ∼ 8 × 10 −10 , X HCS + ∼ 3−7 × 10 −10 ), instead, are 1-2 orders of magnitude larger than predicted in the cloud; on the other hand, they are strongly enhanced on timescales shorter than the shock age (∼2000 years) if CO 2 , S or H 2 S, and OCS are sputtered off the dust grains in the shock. Conclusions. The performed analysis indicates that HCO + and N 2 H + are a fossil record of pre-shock gas in the outflow cavity, whilst HOCO + , SO + , and HCS + are effective shock tracers that can be used to infer the amount of CO 2 and sulphur-bearing species released from dust mantles in the shock. The observed HCS + (and CS) abundance indicates that OCS should be one of the main sulphur carrier on grain mantles. However, the OCS abundance required to fit the observations is 1-2 orders of magnitude larger than observed. Laboratory experiments are required to measure the reactions rates involving these species and to fully understand the chemistry of sulphur-bearing species.

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Heavy water around the L1448-mm protostar

Cited by 62 publications

References 33 publications

Deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B

Deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B

Water in star-forming regions withHerschel(WISH)

Molecular ions in the protostellar shock L1157-B1

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