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Line Radiative Transfer (LRT)
Table of content
Molecular input data files for RT
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(----- The file format is conform to that of the LAMDA database. -----)
.
 | HC3N: hc3n@2007.dat
 | Notes: J=0-50, the energy
level structures and Aij are from CDMS database, while the collision rate coefficients
are extrapolated
to 3~2000 K from accurate data within 5 K < T < 100 K
(from Wernli et al., 2007A&A...464.1147W).
The formula for the extrapolation is from the same paper. Note that some extrapolated collision rate coefficients that show a
stronger rising tendency with temperature may not be correct, e.g., that
of transitions J=49-38, 49-39, etc. |
|
Literature
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| Some issues in molecular line radiative
transfer in magnetic field. The two sources of linear and circular polarization from molecules in B filed:
| Zeeman effect of some
molecule lines (linearly polarized pi,circularly
polarized sigma+ and sigma-
components) have been observed (e.g., H I,
OH and CN). Other candidate molecules that may show
the Zeeman effect are CH, CCS and SO. |
| Goldreich Kylafis effect
(anisotropic radiation field due to velocity gradient in
molecular clouds will cause linear polarization as large as 10-20%. see
Goldreich & Kylafis, 1981ApJ...243L..75G,
1982ApJ...253..606G,
Kylafis, 1983ApJ...267..137K,
1983ApJ...275..135K
and Kylafis & Shapiro 1983ApJ...272L..35K) |
| Anisotropy enduced
linear polarization of astrophysical masers (including radiation
from a star) was discussed (from Western & Watson, 1983ApJ...274..195W,
1983ApJ...275..195W) |
| The degree of linear polarization in
Goldreich Kylafis effect of molecular lines decreases when more more
energy levels are considered (coupling of multiple
levels). Consequently, J=2-1 has lower degree of polarization
than J=1-0. see Deguchi & Watson, 1984ApJ...285..126D) |
| Radiative transfer
equations for linearly polarized maser was presented. (from
Western & Watson, 1983ApJ...268..849W) |
|
| Radiative transfer treatment of hyperfine anomalies (different Tex among hyperfine
lines):
(NH3) Stutzki &
Winnewisser,1985A&A...144...13S
(HCN) Truong-Bach & Nguyen-Q-Rieu,
1989A&A...214..267T
(HCN,CN) Lindqvist et al.,
2000A&A...361.1036L |
| ------------------ Escape
Probability Method ----------------- |
| Escape probability method was extended to spherical
cloud. (from Deguchi & Fukui, 1977PASJ...29..683D) |
| A unified treatment of escape
probabilities in static and moving media.
(from Hummer & Ribicki, 1982ApJ...254..767H) |
| They gave a model grid in the 3-parameter space (Tr,
Nh2, Xco/(dV/dr)) for CO, 1-0 temperature
and CO [2-1]/[1-0] ratio. This grid can be used
to compare with observations to directly constrain the three parameters.
(from Goldsmith et al., 1983ApJS...51..203G) |
| Radiative transfer with dust opacity and thermal balance in a warm dusty medium. (from
Takahashi et al., 1983ApJ...275..145T) |
| The extended the Sobolev approximation with continuum opacity. (from Hummer & Ribicki, 1985ApJ...293..258H) |
| Line overlap applied to OH. (from Doel et
al., 1990MNRAS.244..504D) |
| Sobolev approximation with partial frequency
redistribution. (from Hummer & Ribicki, 1992ApJ...387..248H) |
| They developed a Coupled Escape Probability (CEP)
method for radiative transfer in an exact way. But currently it is only for
plane parallel model. (from Elitzur & Ramos, 2006MNRAS.365..779E) |
| ------------------ Ray
Tracing Method ----------------- |
| A 3D continuum radiative transfer
(step-size controlled, ray-tracing, adaptive multi-wavelength photon
transport grids) code for complex dust configurations around stellar objects
and AGN. (from Steinacker et al., 2003A&A...401..405S) |
| ------------------ Monte
Carlo Method ----------------- |
| A Monte Carlo approach to non-LTE radiative
transfer problems. (from Burnes, 1979A&A....73...67B) |
| RATRAN: An
accelerated Monte Carlo method of 2D radiative
transfer. (from Hogerheijde & van der Tak, 2000A&A...362..697H) |
| ------------------ Others
----------------- |
| Radiative transfer with microturbulence and systematic motions in molcular clouds. (from White, 1977ApJ...211..744W) |
| Collisional-radiative switching -- a
powerful technique for converging non-LTE calculations. (from Hummer &
Voels, 1988A&A...192..279H) |
| They discussed the OH maser line shape under
two limiting assumpions of complete velocity
redistribution and no velocity redistribution.
(from Field et al., 1994A&A...282..213F) |
| An efficient algorithm for 2D radiative transfer.
(from Dullemond & Turolla, 2000A&A...360.1187D) |
| A comparison of different versions of molecular line radiative transfer codes (LI, MC, ALI, AMC and
MULTI) showed that they agree with eath other within 20% accuracy. The largest disagreement is at the location where transition from collision to radiative excitation occurs. These results
may serve as a benchmark for future code developement.
(from van Zadelhoff et al., 2002A&A...395..373V) |
| Compare ray-tracing and
Monte Carlo radiative transfer models in dusty galaxies. (from Semionov & Vansevicius, 2002BaltA..11..537S) |
| Hyperfine structure lines provides information on
optical depths which is otherwise difficult to
obtain (from Schmid-Burgk et al., 2004A&A...419..949S) |
| The primary source of uncertainties
of RT comes from the collision
rate coefficients, the second source is the value of dipole moments. (from Schoier et al., 2005A&A...432..369S) |
| They use radiative transfer model to
determine mass loss rate history of VY CMa.
(from Decin et al., 2006A&A...456..549D) |
Maser observations (back to top)
| ----------HCN masers--------- |
| Discovery of HCN J=1-0 maser in the carbon
star CIT 6. (from Guilloteau et al., 1987). |
| Discovery of stronger HCN J=2-1 maser in
carbon star IRC +10216. (from Lucas &
Cernicharo, 1989) |
| ----------H masers--------- |
| Discovery of H recombination line masers in
emission line source MWC 349. (from
Martin-Pintado et al., 1989) Level population calculations showed the
physical parameter ranges to invert these H recombination line masers. (from
Walmsley 1990) A modeling was shown by Ponomarev et al. (1990). |
| ----------H2O masers--------- |
| Detection of sub-mm H2O masers
4(1,4)-3(2,1) at 380 GHz through Kuiper Airborne Observatory. (Philips
et al. 1980) |
| Detection of sub-mm H2O masers
3(1,2)-2(2,0) at 183 GHz through Kuiper Airborne Observatory. (Waters
et al. 1980, Kuiper et al. 1984) |
| They detected sub-mm H2O maser 10(2,9)-9(3,6)
in both evolved stars and star forming regions at 321 GHz. (from Menten et
al., 1990) |
| Interferometry of H2O
masers in star formation region W49 at
five epochs set up new standard of interstellar H2O masers. W49 is the most
luminous H2O maser in the Galaxy. (from Gwinn et al., 1991) |
| ----------SiO masers--------- |
| SiO masers vary in phase with IR but usually lag by
a 0.2 phase w.r.t. optical light in late type stars. This could be
related to the heating transfered by shocks. (Nyman & Olofsson 1986,
martinez et al. 1988) |
| ----------CH3OH masers--------- |
| ----------NH3 masers--------- |
| Review of masers (by Elitzur, 1992ARA&A..30...75E) |
Maser pumping
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| ----------OH masers---------collisional pump--- |
| Collisional pumping of OH masers (Shapiro & Kaplan 1979, Dixon & field 1979a,b,c, Flower 1979, Elitzur 1979).
The collision with atomic H seems to
supply the most efficient pumping. This mechanism requires collisional rates among rotational levels are
comparable as radiative excitation rates but not to high to cause
collisional thermalization of the rotational levels. This condition may not
be easy to fulfill. |
| Collisional pumping of OH masers by
non-elastic collisions with H2 molecules. This has two effects: 1)
the depopulation of the lower fine structure level of
the ground 2PI3/2 state; 2) the overpopulation
of the higher fine structure levels of the excited 2PI1/2 states,
while the casecade within the 2PI1/2 ladder conserves this character until
the last transition (from 2PI1/2 ladder to 2PI3/2 ladder) in which
overpopulated upper fine structure level particles in 2PI1/2 ladder go into
the lower fine structure level of the ground 2PI3/2 state and the
depopulated fine structure level particles in the 2PI1/2 ladder go into the
higher fine structure level of the ground 2PI3/2 state. Both effects pump
the OH main line masers. However, the collisional
excitation of the 2PI3/2 ladder is a competing mechanism that
destroys the population inversion. (from Andresen et al., 1984A&A...138L..17A) |
| With fairly accurate collision OH-H2 rates
from Dewangan et al. (1987), they demonstated that the in-elastic collisions
can effectly invert masers in the 2PI1/2 lader.
(from Kylafis et al., 1990ApJ...350..209K) |
| ----------OH masers---------radiative pump--- |
| Far IR pumping of OH masers due to
the slight asymmetries in the dipole matrix elements of rotational
transitions. (Elitzur 1978; Lucas 1979a,b; Bujarrabal et
al. 1980A&A....81....1B; Nguyen-Q-Rieu et al. 1979). |
| ----------OH masers---------thermal line overlap pump--- |
| Thermal line overlap pumping of OH
masers. In the case of H II/OH regions, the radiation from a larger warmer cloud can easily pump
OH masers in a smaller cooler OH cloud (from Locus 1979a,b). At larger
column density at which this mechanism is less efficient, thermal overlaps of IR lines within the cloud can
pump maser. The thermal overlap has two major effects: 1) increase the traping of photons and thus reduce the population in
the lower levels of the overlaped lines; 2) tends to mix
(particularly equalize) the populations of the upper levels of two
lines. (Guilloteau et al.,1979) |
| ----------OH masers---------non-local line overlap pump--- |
| Near IR pumping of OH masers is possible due
to the coincidence of H2O emission line and OH absorption line around 2.8
um. (Litvak 1969, Cimerman & Scoville 1979). |
| Far IR line overlap of hyperfine lines as
a more powerful pumping mechanism of OH masers
(Omont 1980IAUS...87..559O). In the case circumstellar OH main line masers,
most gas clumps are receeding from each other, and the line overlaps can produce
masers. Hyperfine components of IR transitions at one location can
overlap with other components at another place. Because in CSE most IR OH
lines are absorption, the overlaps usually enhance the populations of the
lower levels of these IR transitions. The 1667 MHz maser is mainly inverted
by overlaps 5-2, 6-2 and 14-4,
13-3, while the pair 22-2, 21-1 has an
important anti-inverting effect which will dominate when the 35um absorption
is optically thick and thus quench the 1667 MHz masr. The 1665 MHz
maser is mainly inverted by the overlap 23-3, 24-4.
When the 1612 MHz maser is strong, the 1665 MHz maser will be weakened due
to the competetion for populations with the 1612 MHz maser. Here the numbering of enery levels are shown in their paper. (Bujarrabal et al.,
1980A&A....84..311B) |
| ----------OH masers---------miscellaneous discussions--- |
| Pumping of type II OH 1612 masers (Litvak
1969, Elitzur et al. 1976, Elitzur 1976). |
| ----------H2O masers--------- |
| Two temperature collisional pumping of interstellar
H2O masers: collisions with cooler elentron gas and warmer neutral
gas can produce arbitrarily high brightness maser temperatures. (from
Strelnitskij 1980, 1984) |
| An alternative collisional pumping mechanism of
interstellar H2O masers: newly formed H2 molecules are ejected from
grain surface into gas phase in highly excited vibrational states, they
collide with H2O molecules and excite them to high vibrational states,
successive cascading may inert the maser levels. (from Varshalovich et al.,
1983) |
| Collisional pumping of H2O maser is
sufficient to explain observed interstellar H2O masers. (Genzel 1986) |
| Analysis of H2O masers predicted that there should be many more H2O masers
in sub-mm region with comparable
photon lominosity as the famous 22 GHz H2O maser, no matter in
evolved stars or star forming region. (from Cooke & Elitzur 1985,
Elitzur 1989) |
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