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.     

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.     

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.     

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.     

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.     

Origin of diffuse interstellar bands: spectroscopic studies of their possible carriers

The results of astrophysical observations that provide evidence for the molecular origin of the diffuse interstellar bands (DIBs) are reviewed. It is established that molecular systems with a linear, planar or spherical carbon skeleton are good candidates as DIB carriers, and laboratory spectroscopic data concerning such systems are discussed. The characteristic features of the electronic spectra of fullerenes, polycyclic aromatic hydrocarbons, and of linear carbon chains and their ions are found to be consistent with the principal spectroscopic features of DIBs. Analysis of the astrophysical electronic spectra of several simple molecules that have so far been assigned indicates that polar molecules should be easier to detect in this way than those without a permanent electric dipole moment.     

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.     

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.     

Interstellar and circumstellar medium in the direction to IR source IRAS 01005+7910

Using the high-resolution spectra obtained at the 6-meter telescope of the SAO RAS over 2002–2013, we studied the spectral features of the lines of interstellar medium. The radial velocities of the Na I 5890 Å, Na I 5896 Å, Ca II 3934 Å and Ca II 3968 Å absorption lines were analyzed. Seven diffuse interstellar bands 4964, 5780, 5797, 6196, 6203, 6379 Å were identified in the optical spectrum of IRAS01005+7910. Radial velocities V_r and equivalent widths W_λ of these DIBs were measured, for which the values of the interstellar reddening E_B?V and column density of neutral hydrogen log [N(H)] were calculated.     

Origin of the diffuse interstellar absorption bands

The influence of crystal structure and surface stresses on the spectrum of small interstellar particles has been investigated. Surface effects are predicted to result in the occurrence of pairs of features in the discrete absorption spectrum of interstellar dust. A simple relationship between the energy separation between lines of these pairs and their widths is derived which is tested against recent observational data on the diffuse interstellar band spectrum. Thirty of the diffuse bands can be accounted for on this basis by assuming that interstellar dust consists of a mixture of components of differing chemical composition.     

Correlation patterns between 11 diffuse interstellar bands and ultraviolet extinction

We relate the equivalent widths of 11 diffuse interstellar bands, measured in the spectra of 49 stars, to different colour excesses in the ultraviolet. We find that most of the observed bands correlate positively with the extinction in the neighbourhood of the 2175-Å  bump. Correlation with colour excesses in other parts of the extinction curve is more variable from one diffuse interstellar band to another; we find that some diffuse bands (5797, 5850 and 6376 Å) correlate positively with the overall slope of the extinction curve, while others (5780 and 6284 Å) exhibit negative correlation. We discuss the implications of these results on the links between the diffuse interstellar band carriers and the properties of the interstellar grains.     

The identification of diffuse bands

Our present knowledge of the diffuse interstellar bands (two of which were first noted by Wilson in 1958) is briefly summarized. Other broad and very broad interstellar features (the 220nm extinction bump, the very broad structure in the extinction curve, the extended red emission in reflection and other nebulae, and the unidentified-sometimes called the “overidentified”-infrared bands) are also briefly described. The origins of all these features remain unknown, in spite of intensive study. Possible relations between these various features and families is briefly discussed. Recent observations are shown to support the hypothesis that the carriers of the diffuse bands are free-flying molecules, whereas the alternative hypothesis of dust grains now seems to be untenable. Candidate types of molecular carriers are mentioned, and the possible source of such molecules in the diffuse interstellar medium is briefly discussed.     

Optical spectrum of the post-AGB Star HD56126 in the wavelength interval 4010-8790 Å Å

The optical spectrum of the post-AGB star HD56126 identified with the infrared source IRAS07134+1005 is studied in detail using high spectral resolution observations (R = 25000 and 60000) performed with the echelle spectrographs of the 6-m telescope. A total of about one and a half thousand absorptions of neutral atoms and ions, absorption bands of C₂, CN, and CH molecules, and interstellar bands (DIBs) are identified in the 4012 to 8790 Å Å wavelength interval, and the depths and radial velocities of these spectral features are measured. Differences are revealed between the variations of the radial velocities measured from spectral features of different excitation. In addition to the well-known variability of the Hα profile, we found variations in the profiles of a number of FeII, YII, and BaII lines. We also produce an atlas of the spectrum of HD56126 and its comparison star α Per. The full version of the Atlas is available in electronic form from: http://www.sao.ru/hq/ssl/Atlas/Atlas.html.     

Laboratory comparisons of organic materials to interstellar dust and the Murchison meteorite

Spectra of objects which lie along several lines of sight through the diffuse interstellar medium (DISM) reveal an absorption feature near 3.4 micrometers, which has been attributed to saturated aliphatic hydrocarbons on interstellar grains. The similarity of the absorption bands near 3.4 micrometers (2950 cm-1) along different lines of sight indicates that the carrier of this band lies in the diffuse dust. Several materials have been proposed as "fits" to the 3.4 micrometers feature over the years. A comparison of these identifications is presented. These comparisons illustrate the need for high resolution, high signal-to-noise observational data as a means of distinguishing between laboratory organics as matches to the interstellar material. Although any material containing hydrocarbons will produce features in the 3.4 micrometers region, the proposed "matches" to the DISM do differ in detail. These differences may help in the analyses of the chemical composition and physical processes which led to the production of the DISM organics, although ISO Observations through the 5-8 micrometers spectral region are essential for a definitive identification. A remarkable similarity between the spectrum of the diffuse dust and an organic extract from the Murchison meteorite suggests that some of the interstellar organic material may be preserved in primitive solar system bodies. The 3.4 micrometers absorption feature (in the rest frame) has recently been detected in external galaxies, indicating the widespread availability of organic material for incorporation into planetary systems.     

Diffuse interstellar bands in low E (B – V) objects

We analyse spectra of slightly reddened, early-type stars in which the major diffuse interstellar bands at 5870 and 5797 Å are either strong or weak in relation to E(B – V) . It is demonstrated that among the low E(B – V) objects one can find stars obscured by 'sigma' as well as 'zeta' type clouds. The profiles of the diffuse bands seem not to be dependent on the total opacities of the interstellar clouds. We also discuss the physical conditions leading to the formation of the diffuse band carriers in low-opacity interstellar clouds; the carriers are apparently formed in media in which one can observe complex velocity fields.     

Absorption bands and extinction in small interstellar particles

The production of discrete line and broad-band extinction by small interstellar oxide and silicate particles is discussed quantitatively. Restrictions on particle size and refractive index that are required to produce ‘pure’ absorption features are reviewed. The relationship between optical depth in interstellar extinction and absorption coefficients for bulk materials is used to reach some general conclusions concerning the diffuse interstellar features, VUV extinction and the composition of interstellar dust. It is noted that charge transfer bands of ions such as Fe³⁺ may be detectable in the VUV spectrum of dust. Several effects that lead to the enhancement of oscillator strength by 10³–10⁴ in small particles are discussed.     

Diffuse interstellar band formation in dense clouds

Measurements of the strengths of the diffuse interstellar bands at 4430, 5780 and 5797 Å show that the bands tend to be week with respect to extinction in dense interstellar clouds. Data on 10 stars in the ? Ophiuchi cloud complex show further that the diffuse band-producing efficiency of the grains decreases systematically with increasing grain size. It is concluded that the diffuse bands are not formed in the mantles which accrete on the grains in interstellar clouds, but that they could be produced in the cores of grains or in some molecular species.     

The Diffuse λ 2200 Å Interstellar Absorption Band and the Abundances of Neutral Interstellar Hydrogen and Sodium

The equivalent width of the diffuse interstellar absorption band W₂₂₀₀ and the abundances of neutral interstellar hydrogen and sodium derived from the interstellar absorption lines in the spectra of hot stars are well correlated each other.     

Detailed optical spectroscopy of the B[e] Star MWC17

Based on the material of multiple high-resolution R = 60 000 observations conducted on the 6-m telescope (BTA) of the Special Astrophysical Observatory in combination with the Nasmyth Echelle Spectrograph (NES), we closely studied the features of the optical spectrum of the star MWC17 with the B[e] phenomenon. In the wavelength interval of 4050–6750 Å, we identified numerous permitted and forbidden emissions, interstellar Na I lines, and diffuse interstellar bands (DIBs). Radial velocities were estimated from lines of different origin. As the systemic velocity, V_sys, the velocity of the forbidden emissions can be accepted: ?47 kms^?1 (relative to the local standard V_lsr = ?42 kms^?1). Comparison of the obtained data with the earlier measurements allows us to conclude on the absence of considerable variability of spectral details.