Infrared Emission Features Research Articles

Forbidden lines of SI I - an alternate interpretation for an infrared emission feature in the spectrum of SN 1983N (M83)

Interpretation nouvelle des structures spectrales IR observees dans SN 1983N. Le spectre CVF publie par Graham et al en 1986 autour de 1,644 μm, interprete alors en termes de raies [Fe II], est repris en terme d'emission [Si I] pure (raies 1,6454 et 1,6068 μm), en obtenant un resultat aussi bon

Interstellar Polycyclic Aromatic Hydrocarbons and Carbon in Interplanetary Dust Particles and Meteorites

Both interplanetary dust particles (IDP(s)) and meteorites may contain material that is similar to polycyclic aromatic hydrocarbons(PAH(s)). The Raman spectra of IDP(s) and meteorites show features that are similar in position and relative strength to interstellar infrared emission features that have been attributed to vibrational transitions in free, molecular-sized PAH(s). The Raman spectra of some IDP(s) also show red photoluminescence that is similar to the excess red emission seen in some astronomical objects and that has also been attributed to PAH(s) and hydrogenated amorphous carbon. Moreover, a part of the carbonaceous phase in IDP(s) and meteorites contains deuterium to hydrogen ratios that are greater than those for terrestrial samples. Deuterium enrichment is expected in small free PAH(s) that are exposed to ultraviolet radiation in the interstellar medium. Taken together, these observations suggest that some of the carbonaceous material in IDP(s) and meteorites may have been produced in circumstellar dust shells and only slightly modified in interstellar space.

A new emission feature in IRAS spectra and the polycyclic aromatic hydrocarbon spectrum

IRAS spectra of those sources which show strong 7.7 and 11.3 micron emission features also show a plateau of emission extending from 11.3 to about 13.0 microns. Like the 11.3 micron feature, this new feature is attributed to the CH out-of-plane bending mode in polycyclic aromatic hydrocarbons (PAHs). Its discovery reinforces the identification of the 'unidentified infrared emission features' as emission from PAHs. The wavelength of this new feature suggests that interstellar PAHs are not as partially hydrogenated as hitherto thought. It also constrains their molecular structure.

Ionized polycyclic aromatic hydrocarbons and the diffuse interstellar bands

A good case has recently been made that the unidentified infrared emission features arise from positively charged, partially hydrogenated polycyclic aromatic hydrocarbons (PAHs). In this letter it is suggested that these exceedingly stable ions are also the carriers of the diffuse interstellar bands. Although a large variety of PAH isomers is possible, the more condensed forms are substantially more stable than the less condensed forms and are expected to be dominant in the harsh interstellar environment. While neutral PAHs do not absorb in the visible, their ionized counterparts do. Because of their low ionization potential, a substantial fraction of the interstellar PAHs will be ionized. Visible spectra of the most stable PAH cations isolated in glasses are compared directly to the interstellar band spectra. Although the laboratory spectra are on an extremely compressed scale and solid state shifts are present, the comparison is favorable. Since little information is available concerning the spectroscopic properties of these species in the gas phase, a considerable amount of laboratory and theoretical work is called for to test this hypothesis.

Polycyclic aromatic hydrocarbons and the unidentified infrared emission bands - Auto exhaust along the Milky Way

The unidentified infrared emission features (UIR bands) are attributed to a collection of partially hydrogenated, positively charged polycyclic aromatic hydrocarbons (PAHs). This assignment is based on a spectroscopic analysis of the UIR bands. Comparison of the observed interstellar 6.2 and 7.7-micron bands with the laboratory measured Raman spectrum of a collection of carbon-based particulates (auto exhaust) shows a very good agreement, supporting this identification. The infrared emission is due to relaxation from highly vibrationally and electronically excited states. The excitation is probably caused by UV photon absorption. The infrared fluorescence of one particular, highly vibrationally excited PAH (chrysene) is modeled. In this analysis the species is treated as a molecule rather than bulk material and the non-thermodynamic equilibrium nature of the emission is fully taken into account. From a comparison of the observed ratio of the 3.3 to 11.3-micron UIR bands with the model calculations, the average number of carbon atoms per molecule is estimated to be about 20. The abundance of interstellar PAHs is calculated to be about 2 x 10 to the -7th with respect to hydrogen.

Infrared Observations of Interstellar Clouds

A review is given of infrared radiation from interstellar clouds, with emphasis on the new results generated by the IRAS survey. Infrared sources found in the dense cores of cold molecular clouds may be either protostars or embedded T Tauri stars. The dust associated with the diffuse neutral phase of the interstellar medium has been detected by IRAS as the infrared "cirrus". The intensity of the far infrared emission has been correlated with the hydrogen column-density and with the extinction derived from star counts. Very small grains, essentially large molecules, may be responsible both for the unidentified infrared emission features and for the diffuse near and middle infrared emission unexpectedly found in reflection nebulae and in the cirrus.

Excitation mechanisms for the unidentified infrared emission features

view Abstract Citations (78) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Excitation mechanisms for the unidentified infrared emission features. Dwek, E. ; Sellgren, K. ; Soifer, B. T. ; Werner, M. W. Abstract Infrared and radio observations of various objects are analyzed to put observational constraints on the mechanism which gives rise to the unidentified emission features at 3.3, 3.4, 6.2, 7.7, 8.6, and 11.3 microns. The results show that gas-grain collisions or fluorescence is not likely to be the excitation mechanism responsible for the observed features. Thermal emission by dust is reanalyzed and it is concluded that this mechanism can explain the emission features. A simple model in which the emission features arise in a population of small, hot, interstellar grains is constructed. These grains are very efficient radiators, and the emitting materials only need be a minor grain constituent to provide the power that is emitted in the features. The model offers, therefore, a simple explanation for the absence of these features in absorption. Publication: The Astrophysical Journal Pub Date: May 1980 DOI: 10.1086/157967 Bibcode: 1980ApJ...238..140D Keywords: Cosmic Dust; Infrared Astronomy; Infrared Radiation; Molecular Excitation; Thermal Emission; Fluorescence; Interstellar Matter; Nebulae; Ultraviolet Radiation; Astrophysics full text sources ADS | data products SIMBAD (2) Related Materials (1) Erratum: 1981ApJ...243..677D

The peculiar object HD 44179 /'The red rectangle'/

A strong infrared source detected in the AFCRL sky survey is confirmed, and is identified with the binary star HD 44179, embedded in a peculiar nebula. UBVRI and broad-band photometry between 2.2 and 27 microns are combined with blue, red, and near-infrared spectra, polarimetry and spectrophotometry of the star, and a range of direct and image-tube photographs of the nebula, to suggest a composite model of the system. In this model, the infrared radiation derives from thermal emission by dust grains contained in a disklike geometry about the central object, which appears to be of spectral type B9-A0 III and which may be in pre-main-sequence evolution. Two infrared emission features are found, peaking at 8.7 and 11.3 microns, the latter corresponding to the feature seen in the spectrum of the planetary nebula NGC 7027. The complex nebular structure is discussed on the basis of photographs through narrow-band continuum and emission-line filters. The polarization data support the suggestion of a disk containing some large particles. No radio continuum emission is detected.

Complex infrared emission features in the spectrum of beta Lyr.

view Abstract Citations (3) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Complex infrared emission features in the spectrum of Beta Lyrae. Morgan, T. H. ; Potter, A. E. ; Kondo, Y. Abstract Spectra of fl Lyrae over the spectral region 5800-1 1,000 (1.76-0.9 at two different phases have been obtained. They show a remarkable emission-absorption complex at 9231 cm-1, a highly structured emission at P , and several additional broad weak emissions. Subject headings: eclipsing binaries - emission-line stars - spectra, ultraviolet - stars, individual Publication: The Astrophysical Journal Pub Date: June 1974 DOI: 10.1086/152883 Bibcode: 1974ApJ...190..349M full text sources ADS | data products SIMBAD (1)