Rotational contours of CH2X chain species compared with several diffuse interstellar bands

We have calculated synthetic spectra of perpendicular and parallel rovibronic bands of cumulene carbene molecules of the form C _n H₂. The perpendicular bands are consistent with a regularly spaced group of diffuse interstellar bands (DIBs) near 6850 Å. Parallel bands calculated for these molecular structures are consistent with the intrinsic profile of the associated 6614-Å DIB. Both types of bands are expected for an electronic transition that these species should have at those energies. We could not determine if the molecule was charged or if an atom other than carbon terminated the chain-end. Constraints due to molecular geometry and temperature place the chain length at 7–15 carbons to fit the 6850-Å group and 9–13 carbons to fit the 6614-Å DIB.     

On bare carbon chain anions as possible carriers of the diffuse interstellar features

The recent hypothesis that some of the diffuse interstellar bands originate in bare carbon chains such as             and     is tested using echelle spectra covering the whole range of possible (i.e. found in the laboratory) transitions of these molecules. Most of the expected features are below the level of detection in astrophysical spectra, and even those observed show intensity ratios that are different from those in the laboratory. Thus the hypothesis is very unlikely to be true.     

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.     

On the identification of the C60+ interstellar features

The identity of the carriers of the diffuse interstellar bands (DIBs) is one of the most fascinating puzzles of modern spectroscopy. Over the last few years the number of known DIBs has grown substantially. In this paper we discuss the two recently discovered near-infrared weak interstellar features which have already been proposed as fingerprints of the buckminsterfullerene We present and discuss measurements of the two related DIBs within a larger sample of reddened targets, observed with different spectrometers, telescopes and site conditions. We provide additional arguments in favour of the interstellar origin of the two bands. We find evidence around the 9577-Å DIB of far-wing structures, which may affect broad-band measurements. We estimate corrections and errors for telluric and stellar blends, and show that the cores of the two DIBs are well correlated with a ratio near unity within 20 per cent. Finally, we discuss their relation to the laboratory spectra of and the search for two expected weaker transitions.     

Blueshifted diffuse interstellar bands in the spectrum of HD 34078

In this paper, we report the very first observation of diffuse interstellar bands (DIBs) that, in the spectrum of HD 34078 (AE Aur), are blueshifted with respect to the normal position that they have in other objects, where the rest-wavelength velocity frame is determined using very sharp interstellar atomic lines or molecular features. Only reasonably narrow DIBs seemingly show this effect, which is absent in broader ones. The result is confirmed independently using three different spectrographs attached to two different telescopes.     

Rydberg Matter as the dust atmosphere in comets: Spectroscopic and polarization signatures

The long-lived excited state of matter called Rydberg Matter (RM) may explain several spectroscopic features in space, like the diffuse interstellar bands (DIBs) and the unidentified infrared bands (UIR, UIB). RM is here used to interpret some previously unexplained or inconsistent features in comets: (1) line absorption in the emission from the nucleus, (2) IR band emission from the coma, (3) selective and variable molecular line emission from the coma, (4) extended sources of molecules in the coma, (5) degree of linear polarization of light scattered from the coma. (1) The unexplained IR absorptions observed in the flyby of the nucleus of the Comet Borrelly agree well with RM emission bands observed by stimulated emission in the laboratory. It is proposed that RM is the so-called ultrared matter or at least formed from it. (2) The IR bands previously attributed to silicate particles are shown to be better described by RM theory. Transitions in atoms in RM are shown to dominate. (3) The inverted RM medium will optically amplify light from molecular transitions in the comet comae, in agreement with observations that many of the molecular IR emission lines lie within the emission bands from RM, or much too close to Rydberg transitions to be accidental. (4) The unexplained extended sources observed, e.g., for CO are proposed to be due to release of molecules previously incorporated in the RM clusters at low temperature. Such clusters may be the very small particles observed by space probes. (5) Finally, the largely unexplained measurements of the degree of linear polarization of scattered sunlight from comets are explained as due to scattering by the planar RM clusters. Quantitative agreement is demonstrated.     

Very high resolution profiles of four diffuse interstellar bands

Ultra-high-resolution  ( R ∼ 300 000)  profiles of four diffuse interstellar bands (DIBs) are presented. The λλ 5797-, 5850-, 6196- and 6379- Å DIBs were observed towards the reddened supergiant HD 24398, a line of sight free of Doppler splitting; thus the observed profiles can be considered as intrinsic to the DIB carriers. Three of the profiles show substructure which supports the hypothesis of a molecular origin for these DIBs.     

Infrared spectral evolution of carbon stars

We collected almost all Highly Processed Data Products(HPDP)of ISO SWS01 spectra for the Galactic visual carbon stars,infrared carbon stars,extreme carbon stars and carbon-rich proto-planetary nebulae(PPNs).Those infrared spectra are primarily analyzed and discussed.It is shown that either spectral shapes/peaks,or main molecular/dust features are evidenced to change in the sequence of visual carbon stars,infrared carbon stars,extreme carbon stars and carbon-rich PPNs.Statistically,in this sequence,continua are gradually changed from blue to red and locations of spectral peaks of continua are also gradually changed from short wavelengths to long wavelengths.In addition,in this sequence,intensifies of main molecular/dust features are also gradually changed from prominent in the short wavelengths to prominent in the long wavelengths.Furthermore,from 2MASS and IRAS photometric data,the sequence is also proved.Results in this paper strongly support the previous suggestion for the evolution sequence of carbon-rich objects in our Galaxy,that is the sequence of visual carbon stars→infrared carbon stars→extreme carbon stars→carbon-rich PPNs.     

The Discovery of the Chemical Composition - Kinematics Connection in the 1950's

This paper reviews the recognition that kinematic characteristics of stars are related to their spectroscopic appearance on low and intermediate dispersion spectra. These differences result from the differences in the abundances of metals as determined from high dispersion spectra. Presumably, these abundance differences reflect differences in age. The high-velocity carbon stars share the molecular peculiarities of the high-velocity oxygen giants but, because of the greater strength of the bands of carbon-containing molecules, exhibit them to a greater degree. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Cumulenic and heterocumulenic anions: potential interstellar species?

A recent theoretical investigation by Terzieva & Herbst of linear carbon chains, C _n where n  ≥ 6, in the interstellar medium has shown that these species can undergo efficient radiative association to form the corresponding anions. An experimental study by Barckholtz, Snow & Bierbaum of these anions has demonstrated that they do not react efficiently with molecular hydrogen, leading to the possibility of detectable abundances of cumulene-type anions in dense interstellar and circumstellar environments. Here we present a series of electronic structure calculations which examine possible anionic candidates for detection in these media, namely the anion analogues of the previously identified interstellar cumulenes C _n H and C _{n −1}CH₂ and heterocumulenes C _n O (where n  = 2–10). The extraordinary electron affinities calculated for these molecules suggest that efficient radiative electron attachment could occur, and the large dipole moments of these simple (generally) linear molecules point to the possibility of detection by radio astronomy.     

Thermal desorption of CH4 retained in CO2 ice

CO₂ ices are known to exist in different astrophysical environments. In spite of this, its physical properties (structure, density, refractive index) have not been as widely studied as those of water ice. It would be of great value to study the adsorption properties of this ice in conditions related to astrophysical environments. In this paper, we explore the possibility that CO₂ traps relevant molecules in astrophysical environments at temperatures higher than expected from their characteristic sublimation point. To fulfil this aim we have carried out desorption experiments under High Vacuum conditions based on a Quartz Crystal Microbalance and additionally monitored with a Quadrupole Mass Spectrometer. From our results, the presence of CH₄ in the solid phase above the sublimation temperature in some astrophysical scenarios could be explained by the presence of several retaining mechanisms related to the structure of CO₂ ice.     

Numerical Simulations and Astrophysical Applications of Laboratory Jets at Omega

We have conducted experiments on the Omega laser at the University of Rochester that have produced jets of supersonic Ti impacting and being deflected by a ball of high density plastic. These mm-sized jets of dense plasma are highly complex, have large Reynolds numbers, and, given sufficient time and shear, should produce a fully turbulent flow. The experiments are diagnosed with a point-projection backlighter, resulting in a single image per shot. Simulations of the 3D hydrodynamics capture the large-scale features of the experimental data fairly well while missing some of the smaller scale turbulent-like phenomena. This is to be expected given the limited characterization of the targets as well as the finite resolution of the 3D simulations. If Euler scaling holds, these experiments should model larger astrophysical jets in objects such as HH 110 where an outflow can be seen colliding with a molecular cloud. However, Euler scaling demands that not only the isothermal internal Mach numbers of the two systems be similar but also that any dissipative mechanisms, such as radiative cooling or viscous dissipation, be of equal importance relative to each other. Similar equations of state are required as well. We discuss such issues in the context of these experiments and simulations.     

Far-ultraviolet extinction and diffuse interstellar bands

We relate the equivalent widths of the major diffuse interstellar bands (DIBs) near 5797 and 5780 Å with different colour excesses, normalized by E ( B − V ) , which characterize the growth of interstellar extinction in different wavelength ranges. It is demonstrated that the two DIBs correlate best with different parts of the extinction curve, and the ratio of these diffuse bands is best correlated with the far-ultraviolet (UV) rise. A number of peculiar lines of sight are also found, indicating that the carriers of some DIBs and the far-UV extinction can be separated in certain environments, e.g. towards the Per OB2 association.     

One hundred and fifty-three diatomic molecules,molecular ions,and radicals of astrophysical interest

A critical analysis of the 583 available references in literature has been made to select 153 diatomic molecules, molecular ions, and radicals 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 dissociation energy, spectral region, transition levels, astrophysical objects where the respective molecules have been detected (say, comet, meteorite, Sun, planet, star, interstellar matter, Galaxy, etc.); computed theoretical parameters (i.e., FCFs, transition probabilities, r-centroids, PE curves), and available laboratory data with respective references.In many problems involving the estimation of the physical condition (viz., temperature, pressure, density, and abundance) of the emitter, in various cosmic sources, it is desirous to have a knowledge of the theoretical parameters as well as the experimental details for the molecular spectra of interest.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.Besides, some interesting plots of the dissociation energy vs molecular weight, dissociation energy vs total atomic number, dissociation energy vs atomic number differences, ionization potential vs total atomic number, ionization potential vs atomic number differences, and ionization potential vs molecular weight for respective molecules have also been enumerated. Thirty-one new diatomic molecules/molecular ions/radicals of astrophysical significance have also been listed.Astrophysics and Space Science Review Paper.     

Understanding the atmospheric structure of T Tauri stars – I. Improved atomic physics applied to IUE data of BP Tauri

Recent advances in modelling the radiating character of dynamic laboratory and astrophysical plasmas are applied here in a new examination of the properties of the atmosphere of the classical T Tauri star BP Tau. We analyse archived International Ultraviolet Explorer ( IUE ) UV spectra of BP Tau. We adopt a collisional-radiative model and utilize emission measure (EM) and differential emission measure (DEM) techniques to try to constrain the distribution of emitting material in temperature in the atmosphere of this star. We use spectroscopic diagnostic techniques to probe atmospheric parameters such as electron density, and to set constraints on the volume of emission regions. This work is important for understanding the fundamental properties of BP Tau and other T Tauri stars, and for providing a more complete basis for models of their atmospheres.     

The contribution of the direct-transfer mechanism to12C+12C reaction

We investigate the possibility that the¹²C+¹²C reaction proceeds, at low energies (relevant to the carbon burning phase), via direct transfer of an -particle. The exact results depend on the precise value of certain spectroscopic factors, which are, as yet, unknown. A few features of the direct transfer mechanism are emphasized, which might be useful in directing attention to cases where direct transfer is of importance for astrophysical reactions.     

Optical spectrum of the infrared source IRAS 23304+6147

Based on CCD spectra obtained with the PFES echelle spectrometer of the 6-m telescope, we have determined for the first time the effective temperature T _eff=5900 K, surface gravity logg=0.0, and detailed chemical composition of the faint star identified with the infrared source IRAS 23304+6147 by the model-atmosphere method. Its metallicity indicates that the object belongs to the old Galactic disk (the mean abundance of the iron-group elements V, Cr, and Fe for IRAS 23304+6147 is [X/H]=?0.61 dex). The stellar atmosphere exhibits an enhancement of carbon and nitrogen, [C/Fe]=+0.98, [N/Fe]=+1.36, and C/O>1. Significant overabundances of lanthanides were detected: the mean [X/Fe]=+1.04 for La, Ce, Pr, Nd, and Eu. The elemental abundances suggest that the atmospheric chemical composition of IRAS 23304+6147 was modified mainly by nucleosynthesis followed by mixing. By modeling the object's spectrum, we revealed absorption features at the positions of well-known absorption diffuse interstellar bands (DIBs). An analysis of radial-velocity and intensity measurements for these DIBs leads us to conclude that, for IRAS 23304+6147, the DIBs originate mostly in its circumstellar dust envelope expanding at a velocity of about 20 km s^?1. Molecular C₂ Swan emission bands were detected in the object's spectrum, which also originate in the circumstellar envelope. There is a close match between the object's atmospheric effective temperatures determined independently by the model-atmosphere method and by modeling its optical and infrared energy distribution, within the accuracy of the methods.     

Hydrogenated polycyclic aromatic hydrocarbons and the 2940 and 2850 wavenumber (3.40 and 3.51 micron) infrared emission features

The 3150-2700 cm-1 (3.17-3.70 microns) range of the spectra of a number of Ar-matrix-isolated PAHs containing excess H atoms (Hn-PAHs) are presented. This region covers features produced by aromatic and aliphatic C-H stretching vibrations as well as overtone and combination bands involving lower lying fundamentals. The aliphatic C-H stretches in molecules of this type having low to modest excess H coverage provide excellent fits to a number of the weak emission features superposed on the plateau between 3080 and 2700 cm-1 (3.25 and 3.7 microns) in the spectra of many planetary nebulae, reflection nebulae, and H II regions. Higher H coverage is implied for a few objects. We compare these results in context with the other suggested identifications of the emission features in the 2950-2700 cm-1 (3.39-3.70 microns) region and briefly discuss their astrophysical implications.     

TRIMOR – three-dimensional correlation technique to analyse multi-order spectra of triple stellar systems: application to HD 188753

This paper presents a new algorithm, trimor , to analyse multi-order spectra of triple systems. The algorithm is an extension of tricor , the three-dimensional correlation technique that derives the radial velocities of triple stellar systems from single-order spectra. The combined correlation derived from many orders enables the detection and the measurement of radial velocities of faint tertiary companions. The paper applied trimor to the already available spectra of HD 188753, a well-known triple system, yielding the radial velocities of the faintest star in the system. This rendered the close pair of the triple system a double-lined spectroscopic binary, which led to a precise mass ratio and an estimate of its inclination. The close-pair inclination is very close to the inclination of the wide orbit, consistent with the assertion that this triple system has a close to coplanar configuration.