The hyperfine structure of the inversion-rotation transitionJK= ${1}_{0}$ $\leftarrow$ ${0}_{0}$ of NH3investigated by Lamb-dip spectroscopy

Cazzoli, G.; Dore, Luca; Puzzarini, Cristina

doi:10.1051/0004-6361/200912950

Cited by 21 publications

(18 citation statements)

References 21 publications

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“…1 together with the hyperfine structure from Table 3 of Cazzoli et al (2009), adopting the Local Standard of Rest (LSR) velocity (V LSR ) of L1544, 7.2 km s −1 , as reported by Tafalla et al (1998). This is the first observed interstellar o-NH 3 (1 0 −0 0 ) spectrum clearly showing the main groups of hyperfine components.…”

Section: Resultsmentioning

confidence: 54%

“…1. We took into account the hyperfine structure, produced by the electric quadrupole coupling of the N nucleus with the electric field of the electrons, as well as the magnetic hyperfine structure that is due to the three protons (Cazzoli et al 2009). The hyperfine collision rate coefficients were taken from the recent calculations of Bouhafs et al (2017), which, for the first time, include the non-spherical structure of p-H 2 (the main form of H 2 in cold molecular gas, Flower et al 2006;Brünken et al 2014), so that they differ (by up to a factor 2) from those of Maret et al (2009).…”

Section: Discussionmentioning

confidence: 99%

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NH₃(1₀–0₀) in the pre-stellar core L1544

Caselli

Bizzocchi

Keto

et al. 2017

A&A

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Pre-stellar cores represent the initial conditions in the process of star and planet formation, therefore it is important to study their physical and chemical structure. Because of their volatility, nitrogen-bearing molecules are key to study the dense and cold gas present in pre-stellar cores. The NH 3 rotational transition detected with Herschel-HIFI provides a unique combination of sensitivity and spectral resolution to further investigate physical and chemical processes in pre-stellar cores. Here we present the velocityresolved Herschel-HIFI observations of the ortho-NH 3 (1 0 −0 0 ) line at 572 GHz and study the abundance profile of ammonia across the pre-stellar core L1544 to test current theories of its physical and chemical structure. Recently calculated collisional coefficients have been included in our non-LTE radiative transfer code to reproduce Herschel observations. A gas-grain chemical model, including spin-state chemistry and applied to the (static) physical structure of L1544 is also used to infer the abundance profile of ortho-NH 3 . The hyperfine structure of ortho-NH 3 (1 0 −0 0 ) is resolved for the first time in space. All the hyperfine components are strongly selfabsorbed. The profile can be reproduced if the core is contracting in quasi-equilibrium, consistent with previous work, and if the NH 3 abundance is slightly rising toward the core centre, as deduced from previous interferometric observations of para-NH 3 (1, 1). The chemical model overestimates the NH 3 abundance at radii between 4000 and 15 000 AU by about two orders of magnitude and underestimates the abundance toward the core centre by more than one order of magnitude. Our observations show that chemical models applied to static clouds have problems in reproducing NH 3 observations.

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Section: Resultsmentioning

confidence: 54%

Section: Discussionmentioning

confidence: 99%

NH₃(1₀–0₀) in the pre-stellar core L1544

Caselli

Bizzocchi

Keto

et al. 2017

A&A

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“…A review on ammonia is found in Ho & Townes (1983) and an investigation of the hyperfine structure components of the rotational transitions has been performed by Coudert & Roueff (2006) and of ortho-NH 3 at 572 GHz by Cazzoli et al (2009).…”

Section: Transition Frequencymentioning

confidence: 99%

On the accretion process in a high-mass star forming region

Hajigholi

Persson

Wirström

et al. 2016

A&A

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Aims. Our aim is to explore the gas dynamics and the accretion process in the early phase of high-mass star formation. Methods. The inward motion of molecular gas in the massive star forming region G34.26+0.15 is investigated by using high-resolution profiles of seven transitions of ammonia at THz frequencies observed with Herschel-HIFI. The shapes and intensities of these lines are interpreted in terms of radiative transfer models of a spherical, collapsing molecular envelope. An accelerated Lambda Iteration (ALI) method is used to compute the models. Results. The seven ammonia lines show mixed absorption and emission with inverse P-Cygni-type profiles that suggest infall onto the central source. A trend toward absorption at increasingly higher velocities for higher excitation transitions is clearly seen in the line profiles. The J = 3 ← 2 lines show only very weak emission, so these absorption profiles can be used directly to analyze the inward motion of the gas. This is the first time a multitransitional study of spectrally resolved rotational ammonia lines has been used for this purpose. Broad emission is, in addition, mixed with the absorption in the 1 0 -0 0 ortho-NH 3 line, possibly tracing a molecular outflow from the star forming region. The best-fitting ALI model reproduces the continuum fluxes and line profiles, but slightly underpredicts the emission and absorption depth in the ground-state ortho line 1 0 -0 0 . An ammonia abundance on the order of 10 −9 relative to H 2 is needed to fit the profiles. The derived ortho-to-para ratio is approximately 0.5 throughout the infalling cloud core similar to recent findings for translucent clouds in sight lines toward W31C and W49N. We find evidence of two gas components moving inwards toward the central region with constant velocities: 2.7 and 5.3 km s −1 , relative to the source systemic velocity. Attempts to model the inward motion with a single gas cloud in free-fall collapse did not succeed.

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“…Müller et al (1999). A review on ammonia is found in Ho & Townes (1983), and an investigation of the hyperfine structure components of ortho-NH 3 at 572 GHz was recently performed by Cazzoli et al (2009). NH + measurements have been made by Verhoeve et al (1986) and Hübers et al (2009).…”

Section: Observations and Data Reductionmentioning

confidence: 99%

Nitrogen hydrides in interstellar gas

Persson

Luca

Mookerjea

et al. 2012

A&A

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As a part of the Herschel key programme PRISMAS, we have used the Herschel/HIFI instrument to observe interstellar nitrogen hydrides along the sight-lines towards eight high-mass star-forming regions in order to elucidate the production pathways leading to nitrogen-bearing species in diffuse gas. Here, we report observations towards W49N of the NH N = 1-0, J = 2-1, and J = 1-0, ortho-NH 2 N Ka,Kc J = 1 1,1 3/2-0 0,0 1/2, ortho-NH 3 J K = 1 0 -0 0 and 2 0 -1 0 , para-NH 3 J K = 2 1 -1 1 transitions, and unsuccessful searches for NH + . All detections show absorption by foreground material over a wide range of velocities, as well as absorption associated directly with the hot-core source itself. As in the previously published observations towards G10.6−0.4, the NH, NH 2 and NH 3 spectra towards W49N show strikingly similar and non-saturated absorption features. We decompose the absorption of the foreground material towards W49N into different velocity components in order to investigate whether the relative abundances vary among the velocity components, and, in addition, we re-analyse the absorption lines towards G10.6−0.4 in the same manner. Abundances, with respect to molecular hydrogen, in each velocity component are estimated using CH, which is found to correlate with H 2 in the solar neighbourhood diffuse gas. The analysis points to a co-existence of the nitrogen hydrides in diffuse or translucent interstellar gas with a high molecular fraction. Towards both sources, we find that NH is always at least as abundant as both o-NH 2 and o-NH 3 , in sharp contrast to previous results for dark clouds. We find relatively constant N(NH)/N(o-NH 3 ) and N(o-NH 2 )/N(o-NH 3 ) ratios with mean values of 3.2 and 1.9 towards W49N, and 5.4 and 2.2 towards G10.6−0.4, respectively. The mean abundance of o-NH 3 is ∼2 × 10 −9 towards both sources. The nitrogen hydrides also show linear correlations with CN and HNC towards both sources, and looser correlations with CH. The upper limits on the NH + abundance indicate column densities 2-14% of N(NH), which is in contrast to the behaviour of the abundances of CH + and OH + relative to the values determined for the corresponding neutrals CH and OH. Surprisingly low values of the ammonia ortho-to-para ratio are found in both sources, ≈0.5-0.7 ± 0.1, in the strongest absorption components. This result cannot be explained by current models as we had expected to find a value of unity or higher.

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The hyperfine structure of the inversion-rotation transitionJ_K= ${1}_{0}$ $\leftarrow$ ${0}_{0}$ of NH₃investigated by Lamb-dip spectroscopy

Cited by 21 publications

References 21 publications

NH₃(1₀–0₀) in the pre-stellar core L1544

NH₃(1₀–0₀) in the pre-stellar core L1544

On the accretion process in a high-mass star forming region

Nitrogen hydrides in interstellar gas

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The hyperfine structure of the inversion-rotation transitionJK= ${1}_{0}$ $\leftarrow$ ${0}_{0}$ of NH3investigated by Lamb-dip spectroscopy

Cited by 21 publications

References 21 publications

NH3(10–00) in the pre-stellar core L1544

NH3(10–00) in the pre-stellar core L1544

On the accretion process in a high-mass star forming region

Nitrogen hydrides in interstellar gas

Contact Info

Product

Resources

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The hyperfine structure of the inversion-rotation transitionJ_K= ${1}_{0}$ $\leftarrow$ ${0}_{0}$ of NH₃investigated by Lamb-dip spectroscopy

NH₃(1₀–0₀) in the pre-stellar core L1544

NH₃(1₀–0₀) in the pre-stellar core L1544