The rotational structure of methanol and its excitation by helium

Rabli, Djamal; Flower, D. R.

doi:10.1111/j.1365-2966.2010.16240.x

Cited by 30 publications

(23 citation statements)

References 16 publications

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“…The fitted species are listed in the order plotted in Table 2. Note that A-and E-type methanol can only interchange in chemical reactions, but barring peculiar excitation processes, they should be governed by the same partition function (Rabli & Flower 2010).…”

Section: Temperatures and Columns In The Hot Coresmentioning

confidence: 99%

Thermal Feedback in the High-mass Star- and Cluster-forming Region W51

Ginsburg

Goddi

Kruijssen

et al. 2017

ApJ

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Thermal Feedback in the High-mass Star-and Cluster-forming Region W51http://researchonline.ljmu.ac.uk/7346/ Article LJMU has developed LJMU Research Online for users to access the research output of the University more effectively. Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Users may download and/or print one copy of any article(s) in LJMU Research Online to facilitate their private study or for non-commercial research. You may not engage in further distribution of the material or use it for any profit-making activities or any commercial gain.The version presented here may differ from the published version or from the version of the record. Please see the repository URL above for details on accessing the published version and note that access may require a subscription. LJMU Research OnlineThermal Feedback in the High-mass Star-and Cluster-forming Region W51 Abstract High-mass stars have generally been assumed to accrete most of their mass while already contracted onto the main sequence, but this hypothesis has not been observationally tested. We present ALMA observations of a3 1.5 pc area in the W51 high-mass star-forming complex. We identify dust continuum sources and measure the gas and dust temperature through both rotational diagram modeling of CHO H 3 and brightness-temperature-based limits. The observed region contains three high-mass YSOs that appear to be at the earliest stages of their formation, with no signs of ionizing radiation from their central sources. The data reveal high gas and dust temperatures ( > T 100 K) extending out to about 5000 au from each of these sources. There are no clear signs of disks or rotating structures down to our 1000 au resolution. The extended warm gas provides evidence that, during the process of forming, these high-mass stars heat a large volume and correspondingly large mass of gas in their surroundings, inhibiting fragmentation and therefore keeping a large reservoir available to feed from. By contrast, the more mature massive stars that illuminate compact H II regions have little effect on their surrounding dense gas, suggesting that these main-sequence stars have completed most or all of their accretion. The high luminosity of the massive protostars ( > L 10 4  L ), combined with a lack of centimeter continuum emission from these sources, implies that they are not on the main sequence while they accrete the majority of their mass; instead, they may be bloated and cool.

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Section: Temperatures and Columns In The Hot Coresmentioning

confidence: 99%

Thermal Feedback in the High-mass Star- and Cluster-forming Region W51

Ginsburg

Goddi

Kruijssen

et al. 2017

ApJ

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“…On the other hand, the collisional transitions connecting 0 0,0 to the lower 1 1,1 and 2 1,2 states have rate coefficients that are set to zero in the present E-CH 3 OH/p-H 2 data set (Rabli & Flower 2010a). As discussed in Rabli & Flower (2010b), this is an artefact of the coupled state (CS) approximation used in the production of the collision cross sections, and it is very likely that the collisional 0 0,0 −1 1,1 and 0 0,0 −2 1,2 transitions actually have small, but non-zero, rate coefficients. Repeated tests using altered sets of collisional data showed that rate coefficients as small as 3 × 10 −11 cm 3 s −1 (ca.…”

Section: Non-lte Modellingmentioning

confidence: 99%

Deuterated methanol in the pre-stellar core L1544

Bizzocchi

Caselli

Spezzano

et al. 2014

A&A

104

152

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Context. High methanol (CH 3 OH) deuteration has been revealed in Class 0 protostars with the detection of singly, doubly, and even triply D-substituted forms. Methanol is believed to form during the pre-collapse phase via gas-grain chemistry and then eventually injected into the gas when the heating produced by the newly formed protostar sublimates the grain mantles. The molecular deuterium fraction of the warm gas is thus a relic of the cold pre-stellar era and provides hints of the past history of the protostars. Aims. Pre-stellar cores represent the preceding stages in the process of star formation. We aim at measuring methanol deuteration in L1544, a prototypical dense and cold core on the verge of gravitational collapse. The aim is to probe the deuterium fractionation process while the "frozen" molecular reservoir is accumulated onto dust grains. Methods. Using the IRAM 30 m telescope, we mapped the methanol emission in the pre-stellar core L1544 and observed singly deuterated methanol (CH 2 DOH and CH 3 OD) towards the dust peak of L1544. Non-LTE radiative transfer modelling was performed on three CH 3 OH emissions lines at 96.7 GHz, using a Bonnor-Ebert sphere as a model for the source. We have also assumed a centrally decreasing abundance profile to take the molecule freeze-out in the inner core into account. The column density of CH 2 DOH was derived assuming LTE excitation and optically thin emission. Results. The CH 3 OH emission has a highly asymmetric morphology, resembling a non-uniform ring surrounding the dust peak, where CO is mainly frozen onto dust grains. The observations provide an accurate measure of methanol deuteration in the cold pre-stellar gas. The derived abundance ratio is [CH 2 DOH]/[CH 3 OH] = 0.10 ± 0.03, which is significantly smaller than the ones found in lowmass Class 0 protostars and smaller than the deuterium fraction measured in other molecules towards L1544. The singly-deuterated form CH 3 OD was not detected at 3σ sensitivity of 7 mK km s −1 , yielding a lower limit of [CH 2 DOH]/[CH 3 OD] ≥ 10, consistent with previous measurements towards Class 0 protostars. Conclusions. The low deuterium fractionation observed in L1544 and the morphology of the CH 3 OH emission suggest that we are mainly tracing the outer parts of the core, where CO just started to freeze-out onto dust grains.

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“…The first group used the state of the art effective Hamiltonian [91], which included 120 fitting parameters. The second group used a much simpler model [95]. The rotational part H rot was that of the slightly asymmetric top and included the rotational constants A, B, and C (A ≈ B).…”

Section: Molecules With Hindered Rotation: Methanol and Methylaminementioning

confidence: 99%

Microwave and submillimeter molecular transitions and their dependence on fundamental constants

Kozlov

Levshakov

2013

Annalen der Physik

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Microwave and submillimeter molecular transition frequencies between nearly degenerated rotational levels, tunneling transitions, and mixed tunneling-rotational transitions show an extremely high sensitivity to the values of the finestructure constant, α, and the electron-to-proton mass ratio, μ. This review summarizes the theoretical background on quantum-mechanical calculations of the sensitivity coefficients of such transitions to tiny changes in α and μ for a number of molecules which are usually observed in Galactic and extragalactic sources, and discusses the possibility of testing the space-and time-invariance of fundamental constants through comparison between precise laboratory measurements of the molecular rest frequencies and their astronomical counterparts. In particular, diatomic radicals CH, OH, NH + , and a linear polyatomic radical C 3 H in electronic ground state, polyatomic molecules NH 3 , ND 3 , NH 2 D, NHD 2 , H 2 O 2 , H 3 O + , CH 3 OH, and CH 3 NH 2 in their tunneling and tunneling-rotational modes are considered. It is shown that sensitivity coefficients strongly depend on the quantum numbers of the corresponding transitions. This can be used for astrophysical tests of Einstein's Equivalence Principle all over the Universe at an unprecedented level of sensitivity of ∼10 −9 , which is a limit three to two orders of magnitude lower as compared to the current constraints on cosmological variations of α and μ: α/α < 10 −6 , μ/μ < 10 −7 .

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The rotational structure of methanol and its excitation by helium

Cited by 30 publications

References 16 publications

Thermal Feedback in the High-mass Star- and Cluster-forming Region W51

Thermal Feedback in the High-mass Star- and Cluster-forming Region W51

Deuterated methanol in the pre-stellar core L1544

Microwave and submillimeter molecular transitions and their dependence on fundamental constants

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