First Detection of Water Vapor in a Pre-Stellar Core

Caselli, P.; Keto, Eric; Bergin, Edwin A.; Tafalla, M.; Aikawa, Yuri; Douglas, Thomas A.; Pagani, L.; Yıldız, U. A.; Tak, F. F. S. van der; Walmsley, C. M.; Codella, C.; Nisini, B.; Kristensen, L. E.; Dishoeck, E. F. van

doi:10.1088/2041-8205/759/2/l37

Cited by 184 publications

(238 citation statements)

References 49 publications

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“…This is likely due to the L1544 lines presenting two closeby velocity components (Hily-Blant et al 2010b), which are not resolved in the C 15 N spectrum. These two velocity components may be related to the collapse signature recently evidenced by the inverse P-Cygni profile of a water line (Caselli et al 2012).…”

Section: Resultsmentioning

confidence: 69%

The CN/C¹⁵N isotopic ratio towards dark clouds

Hily-Blant

Forêts

Fauré

et al. 2013

A&A

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Understanding the origin of the composition of solar system cosmomaterials is a central question, not only in the cosmochemistry and astrochemistry fields, and requires various approaches to be combined. Measurements of isotopic ratios in cometary materials provide strong constraints on the content of the protosolar nebula. Their relation with the composition of the parental dark clouds is, however, still very elusive. In this paper, we bring new constraints based on the isotopic composition of nitrogen in dark clouds, with the aim of understanding the chemical processes that are responsible for the observed isotopic ratios. We have observed and detected the fundamental rotational transition of C 15 N towards two starless dark clouds, L1544 and L1498. We were able to derive the column density ratio of C 15 N over 13 CN towards the same clouds, and obtain the CN/C 15 N isotopic ratios, which were found to be 500 ± 75 for both L1544 and L1498. These values are therefore marginally consistent with the protosolar value of 441. Moreover, this ratio is larger than the isotopic ratio of nitrogen measured in HCN. In addition, we present model calculations of the chemical fractionation of nitrogen in dark clouds, which make it possible to understand how CN can be deprived of 15 N and HCN can simultaneously be enriched in heavy nitrogen. The non-fractionation of N 2 H + , however, remains an open issue and we propose some chemical way of alleviating the discrepancy between model predictions and the observed ratios.

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Section: Resultsmentioning

confidence: 69%

The CN/C¹⁵N isotopic ratio towards dark clouds

Hily-Blant

Forêts

Fauré

et al. 2013

A&A

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“…In addition, low-mass protostellar objects tend to have an outer abundance of ∼ 10 −8 (Van Dishoeck et al 2011) or even lower (3 × 10 −10 , Mottram et al 2013). Moreover, Snell et al (2000) or Caselli et al (2012) have estimated very low abundances (10 −10 − 10 −8 ) in cold regions. Hence the value derived in our study is compatible with what is found in cold outer regions.…”

Section: The Warm Protostellar Envelopementioning

confidence: 99%

Structure and kinematics of the clouds surrounding the Galactic mini-starburst W43 MM1

Jacq

Braine

Herpin

et al. 2016

A&A

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Massive stars have a major influence on their environment yet their formation is difficult to study as they form quickly in highly obscured regions and are rare, hence more distant than lower mass stars. W43 is a highly luminous galactic massive star forming region at a distance of 5.5 kpc and the MM1 part hosts a particularly massive dense core (1000 M ⊙ within 0.05 pc). We present new Herschel HIFI maps of the W43 MM1 region covering the main low-energy water lines at 557, 987, and 1113 GHz, their H 18 2 O counterparts, and other lines such as 13 CO (10-9) and C 18 O (9-8) which trace warm gas. These water lines are, with the exception of line wings, observed in absorption. Herschel SPIRE and JCMT 450 µm data have been used to make a model of the continuum emission at the HIFI wavelengths. Analysis of the maps, and in particular the optical depth maps of each line and feature, shows that a velocity gradient, possibly due to rotation, is present in both the envelope (r > ∼ 0.5 pc) and the protostellar core (r < ∼ 0.2 pc). Velocities increase in both components from SW to NE, following the general source orientation. While the H 2 O lines trace essentially the cool envelope, we show that the envelope cannot account for the H 18 2 O absorption, which traces motions close to the protostar. The core has rapid infall, 2.9 km s −1 , as manifested by the H 18 2 O absorption features which are systematically red-shifted with respect to the 13 CO (10-9) emission line which also traces the inner material with the same angular resolution. Some H 18 2 O absorption is detected outside the central core and thus outside the regions expected (from a spherical model) to be above 100 K-we attribute this to warm gas associated with the other massive dense cores in W43 MM1. Using the maps to identify absorption from cool gas on large scales, we subtract this component to model spectra for the inner envelope. Modeling the new, presumably corrected, spectra results in a lower water abundance, decreased from 8 10 −8 to 8 10 −9 , with no change in infall rate.

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“…Nonthermal desorption by FUV photons can also be efficient, as shown by laboratory experiments (Öberg et al 2009b,c). Nonthermal desorption dominates in colder regions, either UV-shielded dense cores where secondary UV photons are produced by the interaction between cosmic rays and H 2 molecules (e.g., Caselli et al 2012), or in low-UV-field illumination photo-dissociation regions, where dust grains are too cold to sublimate their ices. This is the case of the Horsehead, where the combination of a moderate-radiation field (χ = 60 relative to the Draine field; Draine 1978), and high density (n H ∼ 10 4 −10 5 cm −3 ) implies low dust grain temperatures, from T dust ∼ 30 K in the outer PDR to T dust ∼ 20 K slightly deeper inside the cloud (Goicoechea et al 2009a).…”

Section: Introductionmentioning

confidence: 99%

The IRAM-30 m line survey of the Horsehead PDR

Guzmán

Goicoechea

Pety

et al. 2013

A&A

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Context. Theoretical models and laboratory experiments show that CH 3 OH is efficiently formed on cold grain surfaces through the successive hydrogenation of CO, forming HCO and H 2 CO as intermediate species.In cold cores and low UV-field illumination photodissociation regions (PDRs) the ices can be released into the gas-phase through nonthermal processes such as photodesorption, which considerably increases their gas-phase abundances. Aims. We investigate the dominant formation mechanism of H 2 CO and CH 3 OH in the Horsehead PDR and its associated dense core.Methods. We performed deep integrations of several H 2 CO and CH 3 OH lines at two positions in the Horsehead, namely the PDR and dense core, with the IRAM-30 m telescope. In addition, we observed one H 2 CO higher-frequency line with the CSO telescope at both positions. We determined the H 2 CO and CH 3 OH column densities and abundances from the single-dish observations complemented with IRAM-PdBI high-angular resolution maps (6 ) of both species. We compared the observed abundances with PDR models including either pure gas-phase chemistry or both gas-phase and grain surface chemistry.Results. We derived CH 3 OH abundances relative to total number of hydrogen atoms of ∼1.2 × 10 −10 and ∼2.3 × 10 −10 in the PDR and dense-core positions, respectively. These abundances are similar to the inferred H 2 CO abundance in both positions (∼2 × 10 −10 ). We find an abundance ratio H 2 CO/CH 3 OH of ∼2 in the PDR and ∼1 in the dense core. Pure gas-phase models cannot reproduce the observed abundances of either H 2 CO or CH 3 OH at the PDR position. The two species are therefore formed on the surface of dust grains and are subsequently photodesorbed into the gas-phase at this position. At the dense core, on the other hand, photodesorption of ices is needed to explain the observed abundance of CH 3 OH, while a pure gas-phase model can reproduce the observed H 2 CO abundance. The high-resolution observations show that CH 3 OH is depleted onto grains at the dense core. CH 3 OH is thus present in an envelope around this position, while H 2 CO is present in both the envelope and the dense core itself. Conclusions. Photodesorption is an efficient mechanism to release complex molecules in low-FUV-illuminated PDRs, where thermal desorption of ice mantles is ineffective.

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First Detection of Water Vapor in a Pre-Stellar Core

Cited by 184 publications

References 49 publications

The CN/C¹⁵N isotopic ratio towards dark clouds

The CN/C¹⁵N isotopic ratio towards dark clouds

Structure and kinematics of the clouds surrounding the Galactic mini-starburst W43 MM1

The IRAM-30 m line survey of the Horsehead PDR

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First Detection of Water Vapor in a Pre-Stellar Core

Cited by 184 publications

References 49 publications

The CN/C15N isotopic ratio towards dark clouds

The CN/C15N isotopic ratio towards dark clouds

Structure and kinematics of the clouds surrounding the Galactic mini-starburst W43 MM1

The IRAM-30 m line survey of the Horsehead PDR

Contact Info

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The CN/C¹⁵N isotopic ratio towards dark clouds

The CN/C¹⁵N isotopic ratio towards dark clouds