The Absorption of Trapped Line Photons by Dust

Goldreich, Peter; Kwan, John

doi:10.1086/156713

Cited by 3 publications

(6 citation statements)

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“…Following Goldreich and Kwan (1974), let us imagine that the 183 GHz population ratio is enhanced because of an excess of decays from the 220 level relative to the 313 level. (Indeed, the ratios of the appropriate probabilities for spontaneous decay, see Figure 6, makes this a plausible mechanism.)…”

Section: B) Excitation Of the Transitionmentioning

confidence: 99%

“…Therefore, for every 183 GHz photon; there must be at least one photon at 2969 GHz. But since the 183 GHz brightness temperature is only 10 to 100 times the excitation temperature of far-IR transition, the The efficiency of collisional pumping by the loss of far-IR line photons is enhanced by the presence of cold dust by a factor of the ratio of the dust optical depth to the line optical depth (Go1dreich and Kwan 1974Kwan , 1979). Gatley ~~.…”

Section: B) Excitation Of the Transitionmentioning

confidence: 99%

“…We note in passing, the near-IR excitation by hot dust is not likely to be an important mechanism. The model proposed by Goldreich and Kwan (1974) is quite general and can be applied with little modification to any transition in the ground vibrational state. It involves excitation to the first vibration state by means of 6 ~m radiation.…”

Section: B) Excitation Of the Transitionmentioning

confidence: 99%

“…To evaluate these possibilities, it is useful to consider the diffusion time for near-IR radiation, which is responsible for heating the dust. Using Goldreich and Kwan's (1974) estimate for the photon mean free path, the diffusion time in years is…”

Section: C) Origin Of the Emissionmentioning

confidence: 99%

“…A hot-gas, cold-dust pump, which also selectively removes 523 -414 photons via an absorption band at 43 ~m, then produces the 22 GHz maser. The 22 GHz emission decays in a time set by the rate at which the gas molecules collide with the dust which, depending on the density, can be weeks to months (e.g., Goldreich andKwan 1974, Deguchi 1981).…”

Section: D) Statistical Equilibrium Modellingmentioning

confidence: 99%

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183 GHz water line variation - an energetic outburst in Orion KL

Kuiper¹,

Kuiper²,

Swanson³

et al. 1984

ApJ

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Observations of the 313-220 transition of water vapour in the direction of Ori MCI in 1980 February show a 50% flux increase and an apparent additional red shift of approximately 2 km s-1 relative to the line observed in 1977 December. We have adapt~d the mm-wave telescope calibration formalism to suit optical telescopes, and included an explicit relation to aperture efficiency to facilitate the use of extended source calibration data with spatially unresolved sources. From a detailed examination of the amplitude and frequency calibration, it appears unlikely that the effect is due to systematic error. The increase is attributed to the appearance of a new component at a velocity of 12 km s-1 with respect to the local standard of rest. The new component also has broad wings. Increased emission from a region in the high-velocity core of Ori MCI can be due either to additional far-IR radiation to pump the 183 GHz transition or to a change in the physical conditions in the gas. We have carried out statistical equilibrium calculations using the large-velocity-gradient formalism to develop a model for the emission and to identify the physical conditions to which the excitation of the 313-202 transition is sensitive. The calculations support a model in which the gas in the region of enhanced emission is hotter than the dust. The temporal coincidence between the 183 GHz increase and the 22 GHz water maser outburst suggests a common, impulsive cause, which has heated the gas in a part of the HV source, enhancing the emission in both transitions.

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Section: B) Excitation Of the Transitionmentioning

confidence: 99%

Section: B) Excitation Of the Transitionmentioning

confidence: 99%

Section: B) Excitation Of the Transitionmentioning

confidence: 99%

Section: C) Origin Of the Emissionmentioning

confidence: 99%

Section: D) Statistical Equilibrium Modellingmentioning

confidence: 99%

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183 GHz water line variation - an energetic outburst in Orion KL

Kuiper¹,

Kuiper²,

Swanson³

et al. 1984

ApJ

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Pumping of Strong H2O Cosmic Masers

Strelnitsky¹

1980

Interstellar Molecules

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Pumping of Strong H₂O Cosmic Masers

Strelnitsky¹

1980

Symp. - Int. Astron. Union

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All the existing models of H2O masers fail to explain such a strong source as W49 N. Observed and theoretical quantities are related by: nH2OWPℓ3 ≳ 1046 S, where S is the maser flux density (in Janskys), nH2O is the H2O number density (cm−3), Wp is pump rate (s−1), and ℓ is the length of amplification region on the line of sight (cm). Models involving vibrational activation (or deactivation) of H2O by H2 (Goldreich and Kwan, 1974; Norman and Silk, 1979), with the usual cross-section σν ≲ 10−19cm2, require ℓ > 1016 cm for the strongest H2O features (∼104 Jy), which is unacceptable in view of the VLBI results. Besides, because σν is so small, it is questionable if vibrational pumping could control rotational level populations at all. Depending on the energy source and sink there are four possible schemes of rotational pumping: CR, RC, RR, and CC (C - collisional, R - radiative). The first was modelled by de Jong (1973) and by Shmeld et al. (1976). Though difficulties with the sink (Goldreich and Kwan, 1974; 1979) are avoidable in the model by Shmeld et al. (Strelnitsky, 1979), ℓ ≳ 1015 − 1016 cm is still required for the strongest features. Therefore other possibilities of rotational pumping are being investigated. One CC-model is presented below.

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The Absorption of Trapped Line Photons by Dust

Cited by 3 publications

References 0 publications

183 GHz water line variation - an energetic outburst in Orion KL

183 GHz water line variation - an energetic outburst in Orion KL

Pumping of Strong H2O Cosmic Masers

Pumping of Strong H₂O Cosmic Masers

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