Interstellar Bands Research Articles

Infrared Spectroscopy of Carbonaceous-chondrite Inclusions in the Kapoeta Meteorite: Discovery of Nanodiamonds with New Spectral Features and Astrophysical Implications

Abstract We report the finding of nanodiamonds, coexisting with amorphous carbon, in carbonaceous-chondrite (CC) material from the Kapoeta achondritic meteorite by Fourier-transform infrared (FTIR) spectroscopy and micro-Raman spectroscopy. In the C–H stretching region (3100–2600 cm−1), the FTIR spectrum of the Kapoeta CC material (KBr pellet) shows bands attributable to aliphatic CH2 and CH3 groups, and is very similar to IR spectra of organic matter in carbonaceous chondrites and the diffuse interstellar medium. Nanodiamonds, as evidenced by micro-Raman spectroscopy, were found in a dark region (∼400 μm in size) in the KBr pellet. Micro-FTIR spectra collected from this region are dramatically different from the KBr-pellet spectrum, and their C–H stretching region is dominated by a strong and broad absorption band centered at ∼2886 cm−1 (3.47 μm), very similar to that observed in IR absorption spectra of hydrocarbon dust in dense interstellar clouds. Micro-FTIR spectroscopy also indicates the presence of an aldehyde and a nitrile, and both of the molecules are ubiquitous in dense interstellar clouds. In addition, IR peaks in the 1500–800 cm−1 region are also observed, which may be attributed to different levels of nitrogen aggregation in diamonds. This is the first evidence for the presence of the 3.47 μm interstellar IR band in meteorites. Our results further support the assignment of this band to tertiary CH groups on the surfaces of nanodiamonds. The presence of the above interstellar bands and the absence of shock features in the Kapoeta nanodiamonds, as indicated by Raman spectroscopy, suggest formation by a nebular-condensation process similar to chemical-vapor deposition.

Interstellar carbon dust

Carbon is the fourth most abundant element in the Universe after hydrogen, helium and oxygen. Synthesized at the late evolutionary stage of stars, carbon is ejected from stars through mass loss of asymptotic giant branch stars and explosion of supernovae and then enters the interstellar medium in the form of ions, atoms, molecules and solid dust particles. Carbon-containing complex organic molecules are essential for the origins of life, and carbonaceous dust is a major component of interstellar grains whose infrared absorption and emission spectra provide a powerful diagnosis of the physical and chemical conditions of astrophysical regions where the dust is found. Carbonaceous dust materials such as graphite, nanodiamonds, polycyclic aromatic hydrocarbon molecules, fullerene, and hydrogenated amorphous carbon are ubiquitously present in the interstellar space and are the most promising candidate carriers of the unidentified 2175 A extinction bump, the unidentified infrared emission bands at 3.3, 6.2, 7.7, 8.6, and 11.3 µm, and the mysterious diffuse interstellar absorption bands. Here we focus on the observational properties of interstellar carbonaceous grains and their physical and chemical characteristics. Also discussed are graphene and carbon nanotubes which may be present in the interstellar space.

C84: A Prototype of Larger Fullerenes. Laboratory Spectroscopy and Astronomical Relevance

We present for the first time the UV/Vis spectrum of the neutral and ionized fullerene C84 isolated in a neon matrix at low temperature. After ionization with high energy (10.2 eV) UV photons, we are able to identify a new spectroscopic absorption band at 718.2 nm that we tentatively attribute to the C84 + ion. We compare the optical spectrum to the diffuse interstellar absorption bands (DIBs) and find eight possible DIBs that fall within the expected shift induced by the solid matrix (± 5 nm) of the assigned C84 + absorption band at 713.6, 713.8, 715.4, 716.1, 718.0, 722.3, 722.4, and 722.8 nm. The astronomical C84 + column density that is required to account for the observed strength of these DIBs is calculated assuming the oscillator strength of the C84 + transition obtained from the laboratory spectrum (f = 0.004). We find that 0.08% and 0.06% of the cosmic carbon abundance would be required to reproduce the 713.6 and 715.4 nm DIB, respectively. A ratio of cosmic C84 + to C60 + of ∼7% or ∼5% is derived based on the assignment of C84 + to the weakest DIBs at 713.6 or 715.4 nm, respectively. Both ratios are in good agreement with the C84 + to C60 + ratio measured in the laboratory under various experimental conditions.

The CH$_\mathsf{2}$CN- molecule: carrier of the $\mathsf{\lambda}$8037 diffuse interstellar band?

The hypothesis that the cyanomethyl anion CH2CN is responsible for the relatively narrow di use interstellar band (DIB) at 8037:8 0:15 A is examined with reference to new observational data. The 0 0 absorption band arising from the 1 B1 ˜ X 1 A 0 transition from the electronic ground state to the first dipole-bound state of the anion is calculated for a rotational temperature of 2.7 K using literature spectroscopic parameters and results in a rotational contour with a peak wavelength of 8037.78 A. By comparison with di use band and atomic line absorption spectra of eight heavily-reddened Galactic sightlines, CH2CN is found to be a plausible carrier of the 8037 di use interstellar band provided the rotational contour is Doppler-broadened with a b parameter between 16 and 33 km s 1 that depends on the specific sightline. Convolution of the calculated CH2CN transitions with the optical depth profile of interstellar Tiii results in a good match with the profile of the narrow 8037 DIB observed towards HD 183143, HD 168112 and Cyg OB2 8a. The rotational level populations may be influenced by nuclear spin statistics, resulting in the appearance of additional transitions from Ka = 1 of ortho CH2CN near 8025 and 8050 A that are not seen in currently available interstellar spectra. For CH2CN to be the carrier of the 8037 di use interstellar band, either a) there must be mechanisms that convert CH2CN from the ortho to the para form, or b) the chemistry that forms CH2CN must result in a population of K 00 levels approaching a Boltzmann distribution near 3 K.

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

We studied in detail the optical spectrum of the post-AGB star HD56126 (IRAS07134+1005). We use high resolution spectra (R=25000 and 60000) obtained with the echelle spectrographs of the 6-m telescope. About one and a half thousand absorptions of neutral atoms and ions, absorption bands of C_2, CN, and CH molecules, and interstellar bands (DIBs) are identified in the 4010 to 8790 AA wavelength region, 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 Halpha 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 staralpha Per. The full version of the atlas is available in electronic form from Web-address: http://www.sao.ru/hq/ssl/Atlas/Atlas.html

Laboratory Simulation of 11-15 μm Spectra Associated with Polycyclic Aromatic Hydrocarbon Molecules

We have obtained 11-15 μm spectra of thin films of hydrogenated amorphous carbon assembled from carbon nanoparticles. Well-defined, narrow features similar to the interstellar emission bands attributed to polycyclic aromatic hydrocarbons (PAHs) are observed at 11.3, 12, 12.8, 13.5, and 14.2 μm. These features are reproduced in many samples prepared under a variety of conditions, indicating that they involve common molecular components. We suggest that these are based on compact ring structures such as coronene, C 24H12, but that these molecules have peripheral substitutions involving additional aromatic rings. They may also be substituted with sp- or sp2-bonded carbon chains. All bands exhibit slight energy shifts in different samples in response to changes in preparation conditions. These shifts replicate variations in wavelength and profile of the 11-15 μm bands seen in different type of emission source. None of the nanoparticle samples exhibit all of the 11.3, 12, 12.8, 13.5, and 14.2 μm features. This implies that the interstellar bands are produced by a limited variety of PAH structures, rather than by a single dominant species.

Nonlinear optics in space

A detailed model for nonlinear photoexcitation of H2in space is proposed and considered at length. It is shown that, on the basis of this model, one is able to provide at least partial explanations for three famous astrophysical spectral mysteries pertaining to our galaxy. These concern the carrier identities of the Diffuse Interstellar (Absorption) Bands (DIBs), the Unidentified Infrared (Emission) Bands (UIBs), and the visible bands emitted by the Red Rectangle nebula.PACS Nos.: 95.30Gv, 33.70-w

B[e] stars

On the basis of spectroscopic CCD material obtained at the Haute Provence Observatory, we provide line identifications and equivalent width measurements in the wavelength region 4095-8935 A of the spectrum of MWC 342. Two hundred eighty emission features are identified and eighteen absorption features. Nine interstellar bands could be identified. Some of the remaining absorption lines correspond to a B0 type star. The cooler emission lines correspond to a spectrum of an early A-type star. The temperatures derived from both spectral types (29 000 and 9 000 K) are in excellent agreement with the temperatures derived by photometrists.

B[e] stars

On the basis of spectroscopic CCD material obtained at the Haute Provence Observatory, we provide line identifications and equivalent width measurements in the wavelength region 4086-8780 Å of the spectrum of MWC 17. Four hundred emission features are identified and seventeen absorption features. Six interstellar bands could be identified. Some of the remaining absorption lines correspond to an early B type star. The emission lines of the envelope correspond approximately to a spectrum of an A0 type star. The star presents variations in the equivalent widths of its lines which correspond to a factor of about two over a time scale of days.

Evidence for a link between the more prominent optical emission bands in the Red Rectangle and some of the diffuse interstellar absorption bands

A re-examination of the spectra of the nebulosity in the Red Rectangle (RR) shows that the wavelengths of the four most prominent emission bands correspond closely with one of the proposed families of diffuse interstellar absorption bands (DIBs). At large offset distances (cooler conditions) from the A0-B8 central star (HD 44179), the emission bands become quite narrow and both the peak wavelengths and widths extrapolate to the observed values for the corresponding DIBs ; this suggests that each pair of the corresponding RR/DIB bands belongs to a common carrier. These emission and absorption features are discussed in terms of electronic transitions in gas-phase molecules

Detection of scattering in the 2175 A interstellar band

Spectrophotometric observations of two reflection nebulae and their illuminating stars obtained with the International Ultraviolet Explorer Satellite have provided the first evidence for the presence of a scattering contribution to the 2175 A interstellar extinction band. Lower than normal far-UV extinction for the stars embedded in the nebulae indicates that the nebulae have a dust particle size distribution that is dominated by larger particles. The strength of the 2175 A band is larger than normal in both cases. The scattering is found to dominate the long-wavelength wing of the band, without shifting the central wavelength of the band by more than 20 A toward longer wavelengths. These observations are taken to indicate that the solid particles responsible for the 2175 A band can be considerably larger than the Rayleigh limit in some interstellar locations. The absence of a notable shift in the central wavelength of the band in such large particles presents a new severe constraint for models of interstellar grains.

Photoelectric photometry of the stars HD 29647 and HDE 283809 in the Taurus dark cloud

Photoelectric Vilnius photometry of the B-type stars HD 29 647 and HDE 283 809 in the direction of the Taurus molecular cloud indicates their brightness and energy distribution to be constant within 1–2%. The interstellar extinction law is determined for the star HDE 283 809 from the photometry data in the Vilnius andUBVRJHKL systems, which yield the ratioR=AV/EB-V=3.5 and grain sizes exceeding the average by approximately 10%. The interstellar extinction law for the two stars is found to be the same in the infrared, however, it is very different in the near ultraviolet. The new spectra of HDE 283 809 confirm the earlier classification and indicate an absence of emission in the hydrogen lines. The interstellar band at 443 nm is observed but its intensity is a half of what is expected forEB-V=1.61. The observed peculiarities of the energy distribution in the spectrum of HDE 283 809 apparently originate in interstellar or circumstellar dust, not in the star itself.

Interstellar diffuse bands in the spectra of six stars previously reported anomalous

Interstellar diffuse bands in the spectra of six stars previously reported anomalous

Laboratory spectra of protosilicates and the interstellar silicate absorption bands

Infrared spectra of submicrometre-sized particles of several protosilicates have been used to derive mass absorption coefficients. These data have been applied in order to describe the infrared radiation from the source OH 26.5+0.6 in terms of a simple model. A good fit of the 10 μm absorption feature could be achieved, but some discrepancies remain in the 20 μm region. The reasons for the weakness of the 20 μm band in infrared sources are discussed.

The 10- and 20-?m interstellar absorption bands: Comparison with the infrared spectrum of the Nogoya meteorite

For submicrometer-sized particles of the carbonaceous chondrite Nogoya and, for comparison purposes, also of terrestrial chamosite, the mass absorption coefficients have been derived from laboratory spectra for the wavenumber range 250–1300 cm−1. Using these data the expected spectrum of an infrared source has been calculated under simple model assumptions and compared with the observed flux from the infrared source OH 26.5+0.6. Although certain discrepancies are left in the 20-μm region it is concluded that phyllosilicates, especially such occurring in carbonaceous chondrites, are interesting candidates for the material of interstellar grains.

An interstellar cloud density from Copernicus observations of CO in the spectrum of Zeta Ophiuchi

Interstellar CO absorption bands in Copernicus spectra of Zeta Oph have been studied. Absorption profiles, computed under the assumption that excitation is due to collisions with H2 molecules and interaction with the 3-K background radiation field, were fitted to the reduced data of nine bands. When a gas kinetic temperature of 56 K is assumed, the best-fit condition implies a hydrogen-nucleus density of 120 per cu cm, a CO column density of 1.2 by 10 to the 15th power per sq cm, and a radial-velocity dispersion of 0.9 km/s. The relevance of these results to existing ideas concerning the Zeta Oph interstellar clouds is discussed. It is suggested that the strongest interstellar component is not circumstellar in origin but is instead part of a supernova remnant. Simple calculations are made to establish the plausibility of the supernova-remnant identification. This suggestion is also supported by Heiles's (1976) 21-cm pictures.

Origin of the diffuse interstellar absorption bands

Origin of the diffuse interstellar absorption bands

The 10-micron interstellar absorption band: Curves of growth for terrestrial and meteoritic olivine particles

Curves of growth have been determined for the interstellar absorption band at 9.75 μm using infrared spectra of small olivine particles. The mass absorption coefficient was found to depend strongly on the mean radius of the grains. A comparison was made with a sample of Allende meteorite and good agreement was found between the curves of growth for terrestrial and meteoritic olivine.

The abundance of negative hydrogen in small hot interstellar clouds

The observed intensities of the diffuse interstellar absorption band at λ 4430 have minimum values, for given stellar distances, that are equivalent to the reddening caused by the small Ambarzumian-type clouds studied by B Stromgren. This indicates that there is no negative hydrogen present between these clouds, which are then identified with the hot H I phase of interstellar matter.

Origin of the diffuse interstellar absorption bands

Origin of the diffuse interstellar absorption bands