arXiv subjects

H. Mutschke

Publications and source records attributed to H. Mutschke.

24 records · Page 2Linked to original sources

arXiv2005

Nanodiamond dust and the far-ultraviolet quasar break

We explore the possibility that the steepening observed shortward of 1000A in the energy distribution of quasars may result from absorption by dust, being either intrinsic to the quasar environment or intergalactic. We find that a dust extinction curve consisting of nanodiamonds, composed of terrestrial cubic diamonds or with surface impurities as found in carbonaceous chondrite meteorites, such as Allende, is successful in reproducing the sharp break observed. The intergalactic dust model is partially successful in explaining the shape of the composite energy distribution, but must be discarded in the end, as the amount of crystalline dust required is unreasonable and would imply an improbable fine tuning among the dust formation processes. The alternative intrinsic dust model requires a mixture of both cubic diamonds and Allende nanodiamonds and provide a better fit of the UV break. The gas column densities implied are of the order 10^{20} cm^{-2} assuming solar metallicity for carbon and full depletion of carbon into dust. The absorption only occurs in the ultraviolet and is totally negligible in the visible. The minimum dust mass required is of the order ~ 0.003 r_{pc}^{2}M_o, where r_{pc} is the distance in parsec between the dust screen and the continuum source. The intrinsic dust model reproduces the flux {\it rise} observed around 660A in key quasar spectra quite well. We present indirect evidence of a shallow continuum break near 670A (18.5 eV), which would be intrinsic to the quasar continuum.

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arXiv2004

Optical data of meteoritic nano-diamonds from far-ultraviolet to far-infrared wavelengths

We have used different spectroscopic techniques to obtain a consistent quantitative absorption spectrum of a sample of meteoritic nano-diamonds in the wavelength range from the vacuum ultraviolet (0.12 $μ$m) to the far infrared (100 $μ$m). The nano-diamonds have been isolated by a chemical treatment from the Allende meteorite (Braatz et al.2000). Electron energy loss spectroscopy (EELS) extends the optical measurements to higher energies and allows the derivation of the optical constants (n & k) by Kramers-Kronig analysis. The results can be used to restrain observations and to improve current models of the environment where the nano-diamonds are expected to have formed. We also show that the amount of nano-diamond which can be present in space is higher than previously estimated by Lewis et al. (1989).

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arXiv2003

Database of optical properties of cosmic dust analogues (DOP)

We present a database containing information on different aspects of calculation and usage of the optical properties of small non-spherical particles -- cosmic dust analogues. The main parts of the DOP are a review of available methods of the light scattering theory, collection of light scattering codes, special computational tools, a graphic library of the optical properties (efficiencies, albedo, asymmetry factors, etc.), a database of the optical constants for astronomy, a bibliographic database of light scattering works, and links to related Internet resources. The general purpose of the DOP having the address http://www.astro.spbu.ru/DOP is twofold -- to help scientists to apply the light scattering theory in astronomy and to give students and beginners a possibility quickly to get necessary knowledge on the subject.

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arXiv2001

Effects of Grain Morphology and Impurities on the Infrared Spectra of Silicon Carbide Particles

In this paper we demonstrate that distinguishing between the polytypes of silicon carbide by means of infrared features in small-grain spectra is impossible. Therefore, the infrared spectra of carbon stars, unfortunately, do not provide a means for drawing comparisons between the crystal structures of grains condensed in these environments and found in meteorites. This is proven first by comparing theoretical band profiles calculated for ellipsoidal particles, which show clearly a strong dependence on the axis ratio of the ellipsoids but negligible differences for the two most common polytypes. Second, spectra measured on submicron particle samples in the laboratory do not show any obvious correlation of band position or shape to the polytype. However, we demonstrate by measurements on SiC whiskers that grain shape is able to determine the spectrum completely. A further strong systematic influence on the band profile can be exerted by plasmon-phonon coupling due to conductivity of the SiC material. The latter fact probably is responsible for the confusion in the astronomical literature about spectral properties of SiC grains. We show that, although the conductivity seems to be a common property of many SiC laboratory samples, it is, however, independent of the polytype.

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arXiv1999

Infrared properties of SiC particles

We present basic laboratory infrared data on a large number of SiC particulate samples, which should be of great value for the interpretation of the 11.3 micron feature observed in the spectra of carbon-rich stars. The laboratory spectra show a wide variety of the SiC phonon features in the 10-13 micron wavelength range, both in peak wavelength and band shape. The main parameters determining the band profile are morphological factors as grain size and shape and, in many cases, impurities in the material. We discovered the interesting fact that free charge carriers, generated e.g. by nitrogen doping, are a very common characteristics of many SiC particle samples. These free charge carriers produce very strong plasmon absorption in the near and middle infrared, which may also heavily influence the 10-13 micron feature profile via plasmon-phonon coupling. We also found that there is no systematic dependence of the band profile on the crystal type (alpha- vs. beta-SiC). This is proven both experimentally and by theoretical calculations based on a study of the SiC phonon frequencies. Further, we give optical constants of amorphous SiC. We discuss the implications of the new laboratory results for the interpretation of the spectra of carbon stars.

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arXiv1998

Infrared Spectra of Meteoritic SiC Grains

We present here the first infrared spectra of meteoritic SiC grains. The mid-infrared transmission spectra of meteoritic SiC grains isolated from the Murchison meteorite were measured in the wavelength range 2.5--16.5 micron, in order to make available the optical properties of presolar SiC grains. These grains are most likely stellar condensates with an origin predominately in carbon stars. Measurements were performed on two different extractions of presolar SiC from the Murchison meteorite. The two samples show very different spectral appearance due to different grain size distributions. The spectral feature of the smaller meteoritic SiC grains is a relatively broad absorption band found between the longitudinal and transverse lattice vibration modes around 11.3 micron, supporting the current interpretation about the presence of SiC grains in carbon stars. In contrast to this, the spectral feature of the large (> 5 micron) grains has an extinction minimum around 10 micron. The obtained spectra are compared with commercially available SiC grains and the differences are discussed. This comparison shows that the crystal structure (e.g., beta-SiC versus alpha-SiC) of SiC grains plays a minor role on the optical signature of SiC grains compared to e.g. grain size.

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