Polyatomic molecules,molecular ions,and radicals of astrophysical interest,i

This paper has been devoted to basic molecular studies of polyatomics. A critical analysis of the 356 available references in literature has been made to select 98 polyatomic molecules, molecular ions, and radicals containing three, four, and five atoms of astrophysical significance. The results have been arranged in a text-cum-tabular form. The compilation contains various information for each molecule, such as the spectral region, transition levels, astrophysical objects, where the respective molecules have been detected (say, comet, meteorite, Sun, planet, star, interstellar matter, interstellar cloud, molecular cloud, interstellar space, Galaxy, etc.).A few important areas of active research in laboratory astrophysics have also been identified in this article: laboratory astrophysics, molecular cloud chemistry, isotopic abundance, planetary and cometary atmospheres through satellites. Seventy-five new polyatomic molecules (containing three, four, and five atoms) of astrophysical significance have also been listed.Astrophysics and Space Science Review Paper I     

Polyatomic molecules,molecular ions,and radicals of astrophysical interest,II

This paper has been devoted to a basic molecular studies of polyatomics. A critical analysis of the 70 available references in literature has been made to select 37 polyatomic molecules, molecular ions, and radicals containing six, seven, eight, nine, ten, eleven, twelve, and thirteen atoms of astrophysical significance. The results have been arranged in a text-cum-tabular form. The compilation contains various information for each molecule, such as the spectral region, transition levels, astrophysical objects where the respective molecules have been detected (say, comet, meteorite, Sun, planet, star, interstellar matter, interstellar cloud, molecular cloud, interstellar space, Galaxy, etc.). Two-hundred fourteen new polyatomic molecules (containing 6, 7, 8, 9, and 10 atoms) of astrophysical significance have also been listed.Astrophysics and Space Science Review Paper II.     

Spectral studies of molecules of astrophysical interest

This paper has been devoted to a minimum amount of literature necessary for an understanding of the spectra of molecules, molecular ions, and radicals present in the cosmic objects such as Sun, comet, interstellar medium, Earth's atmospheres, long period variables, peculiar late-type stars, nebulae, and planetary atmospheres.Astrophysics and Space Science Review Article.     

Radiative recombination in some ions of astrophysical interest

Radiative recombination coefficients for some quadruply and quintuply ionized atoms, present in the Sun and its atmosphere, are investigated in the temperature range 10–10⁴ K by using the method of detailed balance. Simple expressions are given for a quick estimation.     

Small Fe bearing ring molecules of possible astrophysical interest: molecular properties and rotational spectra

A number of small, cyclic molecules containing several carbon atoms in their ring structure has been identified in different astrophysical environments. It is the aim of this work to study important molecular properties of such heterocyclic species bearing an iron atom, which is one of the most abundant cosmic elements. Quantum theoretical calculations based on a density functional approach have been employed to investigate physical properties of six small cyclic carbon and hydrocarbon molecules containing iron as a hetero atom, viz. FeC₂H _n and FeC₃H _n (n=0,2,4). The full geometry optimisation at the chosen level of electronic structure theory (B3LYP/6-31G(d)) including vibrational anharmonicities and non-rigidity, has furnished values for the rotational constants of these species to an expected accuracy of about one per cent. We present structural, electronic, vibrational, and rotational molecular properties including line frequencies, line strengths, and transition probabilities. These results may be helpful for identifying these molecules in future laboratory experiments in view of tentative astronomical observations.     

Autoionization rate coefficients for some ions of astrophysical interest

Autoionization rate coefficients for some quadruply and quintuply ionized atoms have been computed in the temperature range 10⁵–10⁸ K. Typical temperature dependence has been found and simple expressions are given for their quick estimation.     

UV transitions of astrophysical interest in Ge II, As II and Se II

An extensive set of oscillator strengths and transition probabilities has been obtained for the UV transitions originating from the ground 4s²4p ⁿ ( n =1–3) states of Ge II , As II and Se II . These new data, calculated within the framework of a pseudo-relativistic Hartree–Fock (HFR) approach, fill in the gap existing in the atomic data needed for elemental abundance analysis of the interstellar medium. The f values are compared with the rather scarce results previously published in the literature. The astrophysical implications of the new transition rates regarding the interstellar medium are discussed.     

Franck-condon factors and -centroids for certain band systems of astrophysical molecular ions CN+ and N+2

The Franck-Condon factors and r-centroids, which are very closelyrelated to relative vibrational transition probabilities, have beenevaluated by the more reliable numerical integration procedure forthe bands of c ¹ - a ¹ and f ¹ - a ¹ systems of CN ⁺ and C ^{2 +} _u- X ^{2 +} _g and D ² _g- A ² _u systems of N ⁺ ₂ molecular ions of astrophysical interest,using a suitable potential.     

On the detection of interstellar homonuclear diatomic molecules

The pure rotational spectrum of homonuclear diatomic molecules in the interstellar medium is strongly forbidden, and no such spectrum has been detected. In regions of high excitation, vibrational emission may occur, as is widely detected in the case of H₂ in interstellar shocks and photon-dominated regions. However, it is of considerable interest to know the abundance of homonuclear diatomics in quiescent regions. We propose that vibrational emission from homonuclear diatomic molecules in cold clouds may be detectable, where the excitation is mainly through collisions with non-thermal electrons arising from the cosmic-ray ionization of H₂. As an example, we estimate the intensity of emission from N₂ in cold, dark interstellar clouds. We show that such emission is at the limit of detectability with current technology. Other excitation mechanisms may also contribute and enhance this emission.     

Preparation of fine particles of astrophysical interest by gas evaporation techniques

Fine particles of various chemical substances—carbon, iron, iron oxide and silica—which are expected to exist in interstellar space are prepared in argon gas. The size, shape, and crystal structure of the powder particles are studied by electron microscopy and electron diffraction, and may have some bearing on models of comets and of the solar nebula.The largest size we have obtained is about 0.1 μm and the smallest about 40Å. Generally the size becomes smaller for lower temperature and also for lower pressure. This tendency is discussed in connection with nucleation theories. Except for iron and iron oxide the powder particles have no crystal structure.     

Bond dissociation energies and bond orders for some astrophysical molecules

The bond dissociation energies for astrophysically important diatomic molecules have been estimated based on the derived relation D_AB = D_AB + 32.058 Δ_χ where D_AB = (D_AA D_BB)1/2, Δ_χ represents Pauling electronegativity difference χ_A – χ_B) Based on the formula suggested by Reddyet al., bond orders are estimated. The ambiguity arising from Parr & Borkman relation is discussed. The present study supports the view of Politzer thatq/(0.5r _e)² is the correct definition of bond order. The estimated bond energies are in reasonably good agreement with the values in the literature. The bond energies estimated with the relation we suggested, for the molecules in the present study, give an error of 8.0 per cent. The corresponding error associated with Pauling’s equation is 26.8 per cent.     

Forbidden transition probabilities of astrophysical interest among low-lying states of V III

Electric and magnetic multipole transitions among low-lying states of doubly ionized vanadium were computed using the multi-configuration Hartree-Fock (MCHF) method with Breit-Pauli (BP) corrections to a non-relativistic Hamiltonian. Energy levels were determined up to and including 3d ²(¹ G)4s b ² G _7/2 and computed energies were found to be in good agreement with experiment and other theories. In addition to Einstein A _ki coefficients for some E2 and M1 transitions, lifetime data and selected weighted oscillator strengths are also reported.     

The diatomic molecules BH,BN, and BO in sunspots and the solar abundance of boron

Absorption band spectra of BH and BO have been searched for and not found in spectra of sunspots.Electronic oscillator strengths are available only for the A ¹ -X ^{1 +} system of the BH molecule. The absence of the (0,0) band of BH at 4332 Å reflects a solar abundance of boron logA _B<2.5.The band spectra of BN are several orders of magnitude weaker in sunspots than those of BH and BO.Kitt Peak National Observatory Contribution No. 488.Visiting Astronomer, Solar Division, Kitt Peak National Observatory - Operated by The Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

Electron impact broadening of multicharged ion lines of astrophysical interest: Ne VII,Ne VIII and Si XI

The modified semi-empirical method, often used in the investigations of stellar plasma for the determination of needed Stark line widths, is adapted here to use more accurate collision strengths instead of Gaunt factor. It is demonstrated that in such a way its applicability is extended to highly charged ions and good agreement is obtained with the more sophisticated semi-classical perturbation approach up to Si XI. Using this method, Stark line widths of several complex ions: two Be-like ions (Ne VII and Si XI) and one Li-like neon (Ne VIII) were calculated. The obtained results were compared with experiments and other theoretical approaches.     

Measurement of radiative lifetimes and determination of transition probabilities of astrophysical interest in Ho iii

Lifetimes of six levels belonging to the 4f¹⁰6p configuration of Ho  iii have been measured for the first time using the time-resolved laser-induced fluorescence method. They are compared with multiconfigurational pseudo-relativistic Hartree–Fock calculations. A very good agreement is found. Using the experimental lifetimes and theoretical branching fractions, a first set of transition probabilities of astrophysical interest has been obtained for this ion.     

The gravitational instability of flow through porous medium for some systems of astrophysical interest

The gravitational instability of flow through porous medium for some hydrodynamical and hydromagnetical systems of astrophysical interest is investigated. The effects of rotation, magnetic field, viscosity and finite electrical conductivity are studied for the gravitational instability through porous medium. The effect of suspended particles on the instability is also considered. It is found that Jean's criterion remains unchanged in the presence of porosity, viscosity, finite conductivity, rotation, magnetic field and suspended particles in the medium.     

Studies of some diatomic molecules in the F- and early G-type dwarf stars

A critical analysis of CH, NH, OH, C₂, and CN molecules/radicals has been made in twenty-four F- and early G-type dwarfs at different effective temperature as well as in new constructed model atmosphere. Molecular indices of bandheads ofA-X system of CH, NH, OH, C₂, and CN have been obtained by using the data available in the literature (thirteen-colour and eight-colour photometry).Besides, some interesting plots of the molecular indices vs _eff, molecular abundances and molecular indices vs dissociation energy, reduced equivalent widths and FCF's vs dissociation energy for respective molecules have also been enumerated. It is found that the molecular indices at bandheads ofA-X system of CH, NH, OH, C₂, and CN are approximately constant (5810–6570 K). It is to be noted that the molecular indices decrease in the order OH, NH, CH, C₂, and CN at a given temperature.The dissociation equilibrium of CH, NH, OH, C₂, and CN is considered at 5810, 6570, and 7160 K phases in model atmosphere. At standard scale of abundance the molecular abundance and molecular index decrease in the order OH, NH, CH, C₂, and CN at any given phase, however, CN abundance and index increase (_eff=0.867-0.767). The amplitude of abundance and index variation decrease in the order NH, OH, CH, C₂, and CN (_eff=0.767-0.704).The reduced equivalent width decrease in the order OH, NH, CH, and C₂ and FCF's decrease in the order CH, OH, NH, CN, and C₂.The confrontation of models and observations of spectra of F- and early G-type dwarfs of parent molecules is of primary importance to investigate the physical conditions within atmospheres. Reliable excitation models are also requisite for interpreting spectroscopic observations of parent molecules and deriving molecular abundances.     

A plea for better astrophysical and astrometric data in case of double stars of peculiar interest

Summary TheIAU Symposium No. 61 (Perth, 1973, “New Problems in Astrometry’) makes clear that radiosources will play an important role for astrometry in view of the linkage of reference systems. The purposes developed later were to link the various systems from the earth and the solar system to the most inertial possible one. Extragalactic radiosources are the most reliable objects but they are faint. So, intermediate objects are needed. Among them the radiostars, optical objects having radioemission at a certain level and for given frequencies have a fundamental and key position. Most of such radiostars are double or multiple ‘binaries’ as it can be seen from the list of reference stars issued by the Working Group of Commission 24, Working Group created in 1978. The last issue of the core list of radiostars was presented by Ch. de Vegt (Chairman of the WG) on the occasion of the last General Assembly of the IAU (November 1985). A recent study of the system α Scorpii (Antares) has shown that the data concerning the magnitude and the spectral type are not accurate enough, according to the accuracy obtained for the astrometric position (±0 _. ^s 003 for an astrolabe campaign in right ascension). There is also a need for better knowledge about the orbits. In the case of the astrolabe observations, if the distance between the components in <3″ the astrometric position concerns the photocenter and accurate physical properties are needed for comparison with the radio position. Better astrophysical properties are strongly needed for all radiostars to be used as references, during the time the astrometrists have to improve the accuracy of their measurements both in optical and radio fields. Presented by S. Débarbat.     

Experimental and theoretical studies of Dy iii: radiative lifetimes and oscillator strengths of astrophysical interest

The lifetimes of three short-lived levels belonging to the 4f⁹6p configuration and of two long-lived levels of the 4f⁹5d configuration of Dy  iii have been measured for the first time using time-resolved laser-induced fluorescence techniques. They are in good agreement with theoretical values calculated within the framework of a pseudo-relativistic configuration interaction approximation. Using the experimental lifetimes and the theoretical branching fractions, a first set of transition probabilities of astrophysical interest has been obtained for Dy  iii .