An infrared proper motion study of the Orion bullets

We report the first infrared proper motion measurements of the HerbigHaro objects in OMC-1 using a 4-yr time baseline. The [Fe  ii ]-emitting bullets are moving of the order of 0.08 arcsec per year, or at about 170 km s¹. The direction of motion is similar to that inferred from their morphology. The proper motions of H₂-emitting wakes behind the [Fe  ii ] bullets, and of newly found H₂ bullets, are also measured. H₂ bullets have smaller proper motion than [Fe  ii ] bullets, while H₂ wakes with leading [Fe  ii ] bullets appear to move at similar speeds to their associated bullets. A few instances of variability in the emission can be attributed to dense, stationary clumps in the ambient cloud being overrun, setting up a reverse-oriented bullet. Differential motion between [Fe  ii ] bullets and their trailing H₂ wakes is not observed, suggesting that these are not separating, and also that they have reached a steady-state configuration over at least 100 yr. The most distant bullets have, on average, larger proper motions, but are not consistent with free expansion. Nevertheless, an impulsive, or short-lived (<<1000 yr), duration for their origin seems likely.     

A study of the infrared emission of three H II regions S 140–142

The infrared emission of the H II region-molecular cloud complexes S 140, S 141 and S 142 is examined using the IRAS Sky Survey Atlases. The IRAF and Skyview software are used to draw the contour maps of infrared intensity, color temperature and optical depth of each source. The total infrared luminosity and dust distribution in the complexes are given. Compact clumps where star formation probably takes place are identified. The exciter star of S 141 is analyzed.     

The infrared bands of small silicate spheroids

We have investigated the effects of the size, shape, and alignment of small silicate spheroids on the wavelength positions of their absorption bands near 10 m and 20 m. These particles are believed to be a major constituent of interstellar grains and are reported to have been observed in circumstellar dust shells. It is found that the bands for spheroids can be displaced by 1 m towards longer wavelengths from their positions for corresponding spheres; and that a further, though smaller, displacement can be superimposed upon this by their subsequent alignment.Communications from the Royal Observatory, Edinburgh, No. 178.     

A model for the Cl (609 μm) emission of Orion

A model for the energy balance and chemical equilibrium of the gas in photodissociation regions at the edge of molecular clouds, which are illuminated by strong FUV fields (6 eV ≦ hv ≦ 13.6 eV), has been developed. This model is used to calculate the emergent intensities in the fine structure lines of OI (63 μm, 145 μm), CI (609 μm, 370 μm), and CII (158 μm) and in the low-lying rotational transitions of CO. The numerical results show that column densities in the range 2 × 10¹⁷ to 2 × 10¹⁸ cm² can be expected from the C⁺/C/CO transition region at the edge of molecular clouds. This difference with previous chemical calculations is partly due to a higher assumed carbon abundance, partly due to the charge exchange reactions of C⁺ with S and SiO, and partly due to carbon self-shielding which is taken into account. A detailed model is constructed for the Orion photodissociation region, which explains the observed OI (63 μm, 145 μm), CII (158 μm), CI (609 μm), and CO emission. In this model the CI (609 μm) emission originates in the warm (50°K) molecular gas behind Θ¹C Ori but near the surface of OMCI.     

The infrared emission of quasars

A model of two compact components (one contributes at radio and submillimeter wavelength and the other is very small and emits at the infrared region) is proposed to interpret the spectrum of quasi-stellar objects at radio and infrared wavelengths. The physical parameters are estimated from the observed data of 3C 273 for our model and for the model which is derived by assuming the infrared emission as an extrapolation of the synchrotron radio-source. It was proved that our model can explain the observational spectra, while the other model has some difficulties to interpret them completely.This work was partially supported by the Brasilian research agency CNPq     

The excitation of the infrared atmospheric oxygen bands in the nightglow

Simultaneous observations of the nightgiow emission profiles of $\text{O}{}_2\text{(}{}^1\text{Δ)}$ and the OH Meinel bands have been used to show that the excitation mechanism for $\text{O}{}_2\text{(}{}^1\text{Δ)}$ in the night-time is through the reaction between OH¹ and atomic oxygen and the recombination of atomic oxygen. These reactions, and the proposed rate constants, have been used to derive the atomic oxygen profile appropriate to the observations. It is suggested that the atomic oxygen profile may exhibit significant structure near the mesopause at high latitude. It is also suggested that the extent of this structure may be influenced by transport effects related to stratospheric warming events.     

On the infrared bands of A10 related to Mira phenomena

The calculated band positions and intensity factors for the bands of the infraredA-X transition of A10, suggest that an investigation for the infrared bands in the 1 to 5 m region of the spectra of Mira stars and M supergiants, along with the blue-green (B-X) bands, could provide clues to the Mira phenomena. The need for additional laboratory investigation of the infrared electronic transition is emphasized.     

Methanol 72–81A+ emission and some maser series in Orion KL

Methanol 7₂–8₁ A ⁺ is mapped for the first time in Orion KL. Analysing the observed data and solving the statistical equilibrium and radiative transfer equations, it is concluded that line series ofJ ₂–(J+1)₁ A ⁺ (J=7,8,9) is in quasi-thermal emission rather than the masers in Orion KL. The maser spots of methanolJ ₂–J ₁ E (J=6,7) and 8₀–7₁ A ⁺ are distributed in the northeast part of the contour plot of 7₂–8₁ A ⁺. The physical conditions of the regions of maser seriesJ ₀–(J–1)₁ A ⁺ (J=7,8,9) are discussed. Also from the calculation results another maser seriesJ ₁–(J–1)₂ A ^– (J=10,11,12) that might coexist with maser seriesJ ₂–J ₁ E, is found. The sizes of the 2-dimension Gaussian fit plots of methanol 7₂–8₁ A ⁺ and HCOOCH₃ 10(0,10)–9(0,9)A are almost the same, and the main parts overlap each other.     

The infrared emission lines of H2

The photodissociation regions located between ionized regions and molecular clouds are studied by using a one-dimensional model where molecular H₂ are formed on the dust grains, and destructed by photodissociation. The escape probability method is used for the line transfer. The excitation of infrared emission lines of H₂ by UV fluorescence in M17, by shock heating in Orion KL and mainly by UV fluorescence in NGC 2023 are discussed.     

Profiles of blue and infrared diffuse interstellar bands

The paper presents a survey of profiles of reasonably strong diffuse interstellar bands (DIBs) based on the extensive set of high-resolution spectra acquired with the aid of echelle spectrographs installed at the 2-m Terskol, 2-m Pic du Midi and 1-m SAO telescopes. The surveyed diffuse interstellar bands cover the spectral ranges of blue and near-infrared, i.e the DIBs not surveyed by Krełowski & Schmidt . The possible modifications caused by stellar and telluric lines are discussed. The very broad features such as 4430 are not discussed because the shapes of their profiles, extracted from echelle spectra, are very uncertain. The signal-to-noise (S/N) ratios of the spectra are not high enough to enable discussion of the profiles of numerous weak interstellar features discovered recently.     

Investigation of the linear polarization in infrared absorption bands

We consider the effects of the grain size, shape, structure, and chemical composition as well as the angle between the grain rotation axis and the incident ray on the full widths at half maximum (FWHM) of the polarization bands in the two deepest infrared absorption bands observed in the spectra of protostars, the water-ice band centered at 3.1 μm and the silicate band centered at 9.7 μm, using a core—mantle confocal spheroid model with various axial ratios a/b and relative volumes of the core material. We have found that the observed polarization bands with FWHM_p < 0.3 μm in the water-ice absorption band can be explained only by oblate and prolate particles with r _v ≤ 0.35 μm and the polarization bands with FWHM_p ≈ 0.3 μm can be explained only by particles with r _v ≈ 0.35 μm. Broad silicate absorption bands (FWHM ≈ 3 μm) with broad polarization bands (FWHM_p ≈ 2.7 μm) can be explained by particles with r _v ≈ 0.35 μm. Narrow silicate absorption bands (FWHM ≤ 3 μm) with any FWHM of the polarization bands can be explained by a mixture of particles of two types of olivine. Narrow polarization bands (FWHM_p ≈ 2 μm) with broad absorption bands can be explained only by very small particles, r _v ≤ 0.1 μm. We have found the relationships between the effective polarization and extinction cross sections and estimated the ranges of observed polarizabilities that can be explained by particles of given shape and orientation in each of the bands independently. Independent studies of the observational data for each of the bands are shown to give a wider choice of particle model parameters.     

The dynamics of the Orion Nebula

A model is constructed of a spherically symmetric self-gravitating condensation of neutral hydrogen immersed in anHii region. The structure of the condensation is represented by the isothermal gas sphere at a temperature of 100°K. Typical parameters of such a condensation compatible with the estimated ultra-violet radiation field in the central regions of the Orion Nebula are, mass 1M ; radius 10¹⁶ cm; mean density 10^–15 gm cm^–3. The condensations are not static configurations but evolve because of mass loss by ionization from their surfaces. Perhaps 5% become gravitationally unstable and collapse. The remainder act as sources of ionized gas which flows into the surrounding nebula.     

ROSAT PSPC observations of the Orion Trapezium area II. Source variability and revised source list

A deep ROSAT PSPC image centred on the Orion Trapezium has been reduceda second time using an improved version of the PSF to fit the data. The outer rim of the field of view was also included. The new catalogue contains 316 X‐ray sources which are easily identified with pre‐main sequence stars of the Ori OB1 Ic and Id association. All 316 sources were tested for variability. No variations were found inside the single exposures of about 45 minutes length each. Between the 4 exposures spaced over 5 days about 1/3 of the sources show signs of activities of various forms. As above 25% of these have somewhat regular lights curves (monotonically rising or falling or hill‐shaped) we infer that at least some outbursts with time scales longer than a day are present and that past searches for X‐ray flares of pre‐main sequence stars were biased towards shorter time scales.     

Physical parameters of the Orion Bar photodissociation region from radio recombination line observations at 8 mm

Observations of carbon (C), hydrogen and helium (H, He) radio recombination lines (RRLs) at four positions in the Orion Bar photodissociation region (PDR) and toward the center of Orion A have been performed with the RT-22 radio telescope (Pushchino) at 8 mm. The physical parameters of the PDR at these points have been estimated by comparing the carbon RRLs and infrared CII and OI lines. A hydrogen number density in the range 1.2–3.1 × 10⁵ cm^?3 and a mean size of the region along the line of sight (L) in the range 0.006–0.04 pc have been derived. The PDR temperature decreases with increasing distance from the exciting star (θ ¹ C Ori) from 210–230 to 140–150 K (a distance of ≈5′). The data obtained confirm the increase in the PDR size along the line of sight toward the Orion Bar, where, however, L has turned out to be less than the available values in the literature, which can be explained by the presence of clumps in the PDR. A density jump is evident in the Orion Bar region. The PDR zone encompasses the core of the HII region by a thin layer and extends farther, delineating the boundary and the ionization front of the core of the HII region in the Orion Bar and further out the boundary between the halo of the HII region and the molecular cloud. The derived emission measure (EM) toward the Orion Bar has been compared with other C RRL observations. The EM measured from carbon RRLs is EM ≈ 100(±50%) pc cm^?6, imposing constraints on the possible two-component PDR structure. Estimates show that the star θ ¹ C Ori is quite sufficient as a carbon ionization source in the Orion Bar PDR. Some of the data on the ionized hot gas (HII) in this direction have been obtained from H and He RRLs. In particular, the radial velocities (V _lsr) of the HII region are blueshifted with respect to V _lsr of the PDR by 10–17 km s^?1, while the relative ionized helium abundance decreases with increasing distance from the star, indicating that the helium ionization zone is smaller than the ionized hydrogen one.     

The cyanogen bands of Comet Bennett 1970 II

The CN band spectrum of Comet Bennett 1970 II was photographed on April 14, 1970. In addition to the (0,0) band, some other faint lines were observed, which arise either from the (1,1) band of the normal isotopic species or from the (0,0) band of ¹³CN. The Swings effect was investigated theoretically and found to give good agreement with observation. An estimate is made of the pure rotational transition rate in the ground state of CN.Absolute intensities of the CN lines were found by comparison with the lunar spectrum. From these measurements the distribution, density and total mass of cyanogen in the gaseous coma of the comet are estimated.