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The Si2C and SiC2 both are considered to play key role in the formation of the SiC dust grains in the atmosphere of the carbon-rich stars. The molecule of our interest Si2C has been detected in the envelope of the red supergiant star IRC+10216 first time. It is an asymmetric top molecule having electric dipole moment of 1 Debye along the b-axis of inertia. Because of zero nuclear spin of both the Carbon and Silicon atoms, it has only paratransitions. Using the given spectroscopic data (rotational and centrifugal distortion constants and electric dipole moment), for the para-Si2C, we have calculated energies of 200 lower rotational levels (having energy up to 217.8 cm-1) and the Einstein A and B coefficients for 867 radiative transitions between the levels. We have solved a set of 200 statistical equilibrium equations coupled with 867 equations of radiative transfer (Sobolev analysis), where the collisional rate coefficients are taken from a scaling law. Out of 867 radiative transitions, 13 transitions have been found showing weak MASER action, and 19 transitions showing anomalous absorption. One transition 808-717 is found to show both the MASER action as well as the anomalous absorption. These transitions in addition to the observed transitions may play important role in the identification of Si2C in the cosmic objects. [ABSTRACT FROM AUTHOR]

Methylene is an important astrochemical compound. Though its laboratory spectrum was analyzed in 1982, its first unambiguous detection could be feasible after more than one decade in the hot core of Orion-KL nebula and the approximate molecular cloud of the continuum source W51M through its emission line 404-313. Since then waiting of its further detection has now broken as it has been detected in W51 E, W51 M, W51 N, W49 N, W43, W75 N, DR21, and S140 star forming regions, and in W3 IRS5 through the same transition 404-313. To find potential lines of methylene, we have performed Sobolev LVG analysis of each of the ortho and para species of methylene, considering 10 rotational levels having energy up to 324 cm-1. We have found only three lines, 404-313, 505-414 and 212-303 of methylene, which may help for its detection in a cosmic object. The line 212-303 lying at the lowest energy may be more helpful in a cosmic object having low kinetic temperature. [ABSTRACT FROM AUTHOR]

Aminomethanol (NH2CH2OH) and N-Methylhydroxylamine (CH3NHOH) are isomers of each other, and have astrochemical importance. To our knowledge, they have not been analyzed so far in any terrestrial laboratory, and probably due to non-availability of accurate frequencies, they have not been searched in a cosmic object. It is well known that physical conditions in cosmic objects are very different as compared to those in our terrestrial laboratories. Therefore, these molecules may exist in the interstellar medium. For having information about the potential spectral lines of these molecules, we have obtained their rotational and centrifugal distortion constants, and electric dipole moment with the help of the GAUSSIAN software using B3LYP method, and aug-cc-pVDZ and aug-cc-pVTZ basis sets, separately. As the electric dipole moment has comparable components along all the three a, b and c axes, we have considered all the three types of radiative transitions together, and have calculated radiative transition probabilities for all the three kinds of radiative transitions. Considering a, b and c type transitions together, we have performed Sobolev LVG analysis of each molecule, where the collisional rate coefficients have been obtained using a scaling law. Considering energy levels up to 300 cm-1, we have found 181 weak MASER lines and 112 anomalous absorption transitions of NH2CH2OH, and 21 weak MASER lines and 28 anomalous absorption transitions of CH3NHOH, which may play important role for the identification of respective molecule in the ISM. [ABSTRACT FROM AUTHOR]

Using known values of rotational and centrifugal distortion constants in conjunction with electric dipole moment of NH2CHO, we have calculated energies of rotational levels in the ground vibrational state, and the probabilities for radiative transitions between the levels. The radiative transition probabilities in conjunction with the scaled values of collisional rate coefficients are used in the Sobolev LVG analysis of NH2CHO. There are some strong lines. For ortho-NH2CHO, we have found one transition 110-111 showing anomalous absorption and five transitions 615-514, 717-616, 716-615, 818-717, 817-716 showing emission feature. For para-NH2CHO, six emission transitions 505-404, 606-505, 707-606, 808-707, 909-808, 100.10-909 are found. Out of these 12 transitions, three transitions, 110-111, 505-404, and 808-707, are already found in the ISM. Other relatively weaker lines are also found in the ISM. In addition to the observed lines, 9 transitions may play important role in the identification of NH2CHO in a cosmic object. [ABSTRACT FROM AUTHOR]

Cyanamide (NH2CN) has pyramidal equilibrium structure with two substates, denoted by 0+ and 0–. For each state of NH2CN, knowing rotational and centrifugal distortion constants in conjunction with electric dipole moment, energies for rotational levels and the probabilities for radiative transitions between the levels are calculated. The radiative transition probabilities in conjunction with scaled values for rate coefficients for collisional transitions between the levels are used in the Large Velocity Gradient analysis for each substate. For each substate, we have found anomalous absorption in three doublets at high temperature and weak MASER action at low temperature. We have also found emission feature in nine transitions in each substate. These transitions, along with the observed ones, may play important role for identification of NH2CN in a cosmic object. [ABSTRACT FROM AUTHOR]

The emission from the gas behind the front of a stationary shock wave is calculated for the conditions in the atmospheres of red dwarf stars for velocities u0 from 30 to 100 km/s. Energy exchange between the electron and atom-ion components is taken into account through elastic collisions, free-free, bound-bound, and bound-free collisional and radiative transitions of hydrogen in the radiation field of a star's photosphere. Cooling by the following chemical elements is included: C, N, O, Mg, Si, S, Ca, and Fe. The following results are obtained: the post-shock gas remains transparent in the optical range of the continuum throughout the emission time; hence, it cannot be a source of the black-body radiation that appears at times during flares. The recombination and bremsstrahlung radiation of the transparent gas, as well as the flux in the Balmer series lines represent a few percent of the energy flux of matter through the viscous jump. The ratio of the fluxes in the spectrum lines and the continuum depends on u0 and on the parameters of the atmosphere. These results are consistent with the idea of multicomponent emission in flares, specifically, line emission is determined by the shock wave in layers above the photosphere, while black-body radiation comes from the photosphere heated by a flux of suprathermal particles. [ABSTRACT FROM AUTHOR]

The purpose of this article is to provide some insight into Ambartsumian’s methods in the theory of radiative transfer, their applications, and further development. Two of these methods are emphasized--the invariance principle and the method of addition of layers, proposed by Ambartsumian in the 1940’s. The difference between these methods and the classical approach for solving radiative transfer problems is discussed. We discuss only a small portion of the subsequent work by others that we believe reveals, in a more intuitive way, the essence and significance of Ambartsumian’s methods and their efficiency for applications. Thus, for example, a separate section is devoted to applications of the Lagrangian formalism to radiative transfer and it is shown that the invariance principle is a special case of a more general variational principle that reflects an invariance with respect to translational transformation of the optical depth. Our discussion of the method of addition of layers points out its generality and the major role it has played in the later creation of such methods as Bellman’s invariant imbedding method and the method for solving radiative transfer problems in inhomogeneous media. The latter method has yielded a number of new analytic results. The concluding section is a brief summary of Ambartsumian’s results in the nonlinear theory of radiative transfer, where he was a pioneer in the study of the class of multilevel problems. This article also sets out to demonstrate the place and role of Ambartsumian’s methods in the theory of radiative transfer, which, to a great extent, set the path along which this theory developed for many years to come. [ABSTRACT FROM AUTHOR]