Study of CO line profiles in molecular clouds - Relaxing the assumption of complete frequency redistribution

1982 ◽  
Vol 260 ◽  
pp. 579 ◽  
Author(s):  
S. Deguchi ◽  
J. Kwan
Keyword(s):  
Molecular Clouds ◽  
Line Profiles ◽  
Frequency Redistribution ◽  
Complete Frequency

scholarly journals Hydrogen Line Profiles

1995 ◽  
Vol 10 ◽  
pp. 411-414 ◽  
Author(s):  
I. Hubeny
Keyword(s):  
Transfer Problem ◽  
Current Status ◽  
Line Profiles ◽  
Line Broadening ◽  
Hydrogen Line ◽  
Radiative Transfer Problem ◽  
Frequency Redistribution ◽  
Sufficient Detail ◽  
High Degree ◽  
Complete Frequency

Observed hydrogen line profiles are an enormously important source of diagnostic information about virtually all kinds of astronomical bodies. Therefore, it is important to understand the hydrogen line formation in sufficient detail to be able to achieve a high degree of reliability by analyzing observed hydrogen line profiles.Calculation of the predicted hydrogen line profiles involves two basic ingredients, (i) intrinsic line profiles, or line broadening - ”atomic physics” part, and (ii) the radiative transfer problem - ”astrophysics” part. There is not enough space to discuss here the current status of the astrophysical part of the problem. Fortunately, this topic is covered by many reviews. There are two major problems here, (a) departures from local thermodynamic equilibrium (LTE) - the so-called non-LTE description (e.g. Mihalas 1978; Hubenyet al.1994); and (b) departures from complete frequency redistribution (Cooperet al.1989; Hubeny and Lites 1994).

scholarly journals Semi-empirical model atmospheres for the chromosphere of the sunspot penumbra and umbral flashes

2019 ◽  
Vol 627 ◽  
pp. A46 ◽  
Author(s):  
Souvik Bose ◽  
Vasco M. J. Henriques ◽  
Luc Rouppe van der Voort ◽  
Tiago M. D. Pereira
Keyword(s):  
Transition Region ◽  
Empirical Model ◽  
Solar Chromosphere ◽  
Line Profiles ◽  
Frequency Redistribution ◽  
Lower Transition ◽  
Semi Empirical ◽  
Complete Frequency ◽  
Imaging Spectrograph ◽  
Sunspot Penumbra

Context. The solar chromosphere and the lower transition region are believed to play a crucial role in the heating of the solar corona. Models that describe the chromosphere (and the lower transition region), accounting for its highly dynamic and structured character are, so far, found to be lacking. This is partly due to the breakdown of complete frequency redistribution (CRD) in the chromospheric layers and also because of the difficulty in obtaining complete sets of observations that adequately constrain the solar atmosphere at all relevant heights. Aims. We aim to obtain semi-empirical model atmospheres that reproduce the features of the Mg II h&k line profiles that sample the middle chromosphere with focus on a sunspot. Methods. We used spectropolarimetric observations of the Ca II 8542 Å spectra obtained with the Swedish 1 m Solar Telescope and used NICOLE inversions to obtain semi-empirical model atmospheres for different features in and around a sunspot. These were used to synthesize Mg II h&k spectra using the RH1.5D code, which we compared with observations taken with the Interface Region Imaging Spectrograph (IRIS). Results. Comparison of the synthetic profiles with IRIS observations reveals that there are several areas, especially in the penumbra of the sunspot, where most of the observed Mg II h&k profiles are very well reproduced. In addition, we find that supersonic hot down-flows, present in our collection of models in the umbra, lead to synthetic profiles that agree well with the IRIS Mg II h&k profiles, with the exception of the line core. Conclusions. We put forward and make available four semi-empirical model atmospheres. Two for the penumbra, reflecting the range of temperatures obtained for the chromosphere, one for umbral flashes, and a model representative of the quiet surroundings of a sunspot.

Effects of Ambipolar Diffusion on Prominence Thread Models

1994 ◽  
Vol 144 ◽  
pp. 315-321 ◽  
Author(s):  
M. G. Rovira ◽  
J. M. Fontenla ◽  
J.-C. Vial ◽  
P. Gouttebroze
Keyword(s):  
Energy Balance ◽  
Transition Region ◽  
Ambipolar Diffusion ◽  
Line Profiles ◽  
Balance Equations ◽  
Model Calculations ◽  
Partial Frequency ◽  
Frequency Redistribution ◽  
Partial Frequency Redistribution ◽  
Theoretical Structure

AbstractWe have improved previous model calculations of the prominence-corona transition region including the effect of the ambipolar diffusion in the statistical equilibrium and energy balance equations. We show its influence on the different parameters that characterize the resulting prominence theoretical structure. We take into account the effect of the partial frequency redistribution (PRD) in the line profiles and total intensities calculations.

High resolution J = 2 - 1 and J = 1 - 0 carbon monoxide self-reversed line profiles toward molecular clouds

1981 ◽  
Vol 245 ◽  
pp. 495 ◽  
Author(s):  
R. B. Loren ◽  
R. L. Plambeck ◽  
J. H. Davis ◽  
R. L. Snell
Keyword(s):  
Carbon Monoxide ◽  
High Resolution ◽  
Molecular Clouds ◽  
Line Profiles ◽  
Reversed Line

scholarly journals Molecular Outflows

1989 ◽  
Vol 120 ◽  
pp. 231-243
Author(s):  
Ronald L. Snell
Keyword(s):  
Carbon Monoxide ◽  
Sound Speed ◽  
Molecular Clouds ◽  
Molecular Form ◽  
Line Profiles ◽  
Internal Dynamics ◽  
Molecular Outflows ◽  
Submillimeter Spectroscopy ◽  
Line Widths ◽  
Co Emission

The development of millimeter and submillimeter spectroscopy has allowed astronomers to probe the cold, dense component of the interstellar medium. This medium, primarily composed of gas in molecular form, is gravitationally bound into relatively distinct clouds that are sites of star formation within our Galaxy. The most ubiquitous tracers of these molecular clouds are the rotational transitions of carbon monoxide. Observations of CO emission have been commonly used to estimate the size, temperature, mass, and density of molecular clouds; in addition, the spectral line profiles can be used to study the internal dynamics of these clouds. Although the sound speed within molecular clouds is only about 0.2 km s−1, observed CO line widths are more typically 1 to 5 km s−1. Thus, the internal dynamics of molecular clouds are characterized by supersonic gas motions whose nature is poorly understood.

scholarly journals Line radiation transfer in non-equilibrium laser plasma

1988 ◽  
Vol 6 (4) ◽  
pp. 703-708
Author(s):  
S. I. Kaśkova ◽  
G. S. Romanov ◽  
K. L. Stepanov
Keyword(s):  
Spectral Line ◽  
Source Function ◽  
Radiation Transfer ◽  
Resonance Scattering ◽  
Plasma Radiation ◽  
Line Profiles ◽  
Radiation Characteristics ◽  
Laser Target ◽  
Line Radiation ◽  
Frequency Redistribution

The self-radiation characteristics of plasma created under the effect of a powerful laser radiation on a target are considered. The radiation in the spectral range from 1 to 1300 Å is calculated in coherent assumption for given gas-dynamic fields corresponding to various phases of laser target explosion. The source function was determined in accordance with a plasma radiation-collision model with the assumption of its transparency. Calculations show that the contribution of line radiation to the total flux may be from 20 to 60%. Mainly, this paper considers radiation transfer. The effect of self-radiation on level populations and frequency redistribution at resonance scattering is taken into account. The resonance scattering is predominant in the coronal plasma. Exit of photons from deeper layers of the target in comparison with the coherent case increases. Macroscopic plasma motion leading to spectral line shift is taken into consideration in the calculations. Output radiation spectral intensity distribution in oxygen and silicon H-like ions resonance lines has been determined. Spectral line profiles calculated with account of basic broadening mechanisms were used.

scholarly journals Methanol at the Edge of the Galaxy: New Observations to Constrain the Galactic Habitable Zone

2021 ◽  
Vol 922 (2) ◽  
pp. 106
Author(s):  
J. J. Bernal ◽  
C. D. Sephus ◽  
L. M. Ziurys
Keyword(s):  
Molecular Clouds ◽  
Organic Molecules ◽  
Galactic Center ◽  
Solar Neighborhood ◽  
Habitable Zone ◽  
Line Profiles ◽  
Galactocentric Distance ◽  
Radio Observatory ◽  
The Galaxy ◽  
Co Observations

Abstract The Galactic Habitable Zone (GHZ) is a region believed hospitable for life. To further constrain the GHZ, observations have been conducted of the J = 2 → 1 transitions of methanol (CH3OH) at 97 GHz, toward 20 molecular clouds located in the outer Galaxy (R GC = 12.9–23.5 kpc), using the 12 m telescope of the Arizona Radio Observatory. Methanol was detected in 19 out of 20 observed clouds, including sources as far as R GC = 23.5 kpc. Identification was secured by the measurement of multiple asymmetry and torsional components in the J = 2 → 1 transition, which were resolved in the narrow line profiles observed (ΔV 1/2 ∼ 1–3 km s−1). From a radiative transfer analysis, column densities for these clouds of N tot = 0.1–1.5 × 1013 cm−2 were derived, corresponding to fractional abundances, relative to H2, of f (CH3OH) ∼ 0.2–4.9 × 10−9. The analysis also indicates that these clouds are cold (T K ∼ 10–25 K) and dense (n(H2) ∼ 106 cm−3), as found from previous H2CO observations. The methanol abundances in the outer Galaxy are comparable to those observed in colder molecular clouds in the solar neighborhood. The abundance of CH3OH therefore does not appear to decrease significantly with distances from the Galactic Center, even at R GC ∼ 20–23 kpc. Furthermore, the production of methanol is apparently not affected by the decline in metallicity with galactocentric distance. These observations suggest that organic chemistry is prevalent in the outer Galaxy, and methanol and other organic molecules may serve to assess the GHZ.

scholarly journals Signatures of turbulence in the dense interstellar medium

1991 ◽  
Vol 147 ◽  
pp. 119-136
Author(s):  
E. Falgarone ◽  
T.G. Phillips
Keyword(s):  
Interstellar Medium ◽  
Turbulent Flows ◽  
Fractal Geometry ◽  
Molecular Clouds ◽  
Large Range ◽  
Line Profiles ◽  
Physical Processes ◽  
Molecular Line ◽  
Scale Size ◽  
Excitation Conditions

We present an ensemble of recent observational results on molecular clouds which, taken separately, could all be understood by invoking various unrelated physical processes, but taken all together form a coherent ensemble stressing the imprints of turbulence in the physics of the cold interstellar medium. These results are first, the existence of wings in the molecular line profiles, which can be interpreted on statistical grounds as the signature of the intermittency of the velocity field in turbulent flows, second the fractal geometry of the cloud edges, with properties reminiscent of those of various surfaces studied in turbulent laboratory flows, and third, the fact that the dense gas fills only a very small fraction of the space. The last points are supported by CO multitransition observations of a few fields in nearby molecular clouds. They show that the excitation conditions are the same for the gas emitting in the linewings and in the linecores and are also remarkably uniform over a large range (factor 10) of column densities. An attractive interpretation of the molecular line data is that most of the 12CO(J=2—1) and (J=3—2) emissions arise in cold (Tk ≥ 10K) and dense (nH2 ∼ 104cm—3 or more) structures distributed on a fractal set with no characteristic scale size greater than about 1000 AU.

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