A. Borghesi

The absorption efficiency of submicron amorphous carbon particles between 2.5 and 40 μm

Abstract Submicronic amorphous carbon particles have been studied in the near-and middle-infrared at room temperature and their properties measured. Two different production methods have been used: (a) arc striking in an argon controlled atmosphere; (b) burning of hydrocarbons in air. TEM analysis allows determination of grain morphology and size distributions. Particle shapes appear to be influenced by different production methods, established by comparing our results with those of samples produced by means of focused laser pulses. Grain dimensions are strongly ambient pressure dependent since collisional growth is active in particle formation. All the absorption extinction curves indicate a general λ −1 fall-off, with small humps at 8, 11 and 12 μm. A band at about 13 μm is observed only for grains obtained by burning hydrocarbons. Possible temperature effects on the absorption wavelength dependence have been noted by comparing our observations with those of commercial lamp-black performed at liquid helium temperature.

The absorption properties of submicron SiC particles between 2.5 and 40 μm

Abstract Submicron α-SiC particles have been studied in the near and middle i.r. at room temperature and their properties measured after different treatment processes: namely, grinding, ultrasonic washing and sedimentation. TEM analysis allows determination of grain morphology and size distributions. The extinction curves reveal the presence of a central main peak at 11.4 μm and of two shoulders, respectively at 10.6 and 12.7 μm, due to phonon resonances. Our data show good agreement with those previously reported by the University of Jena Group. On the other hand, β-SiC spectra differ substantially, indicating their crucial dependence on the crystallographic characteristics of the samples. Experimental astronomical observations seem to indicate that α-SiC is the best candidate to simulate the actual SiC present in cosmic sources.

2.5-300 μm laboratory observations of submicron SiC particles as cosmic dust candidates

Abstract Three different kinds of α-SiC and one β-SiC sample which have undergone the same treatment procedures have been studied morphologically. Their absorption spectra have also been measured in the range 2.5–300 μm. Outside the typical 11.5 μm absorption band, all spectra show an FIR trend which can be fitted by a power law λ -γ . The steepness is seen to increase as a function of sample purity. For the highest purity, 99.3%, γ = 1.4. The lowest values are interpreted as being due to the presence of some contaminants in the samples, metallic Fe mainly and also free C and free SiO. β-SiC also shows a λ -γ spectrum with γ ≅ 1.0, while that measured by Tanabe et al. 7 is found to be characterized by γ = 1.4 again. This difference is tentatively interpreted as being due to a higher purity of the Japanese group sample. The results of our analysis seem to suggest that α-SiC and β-SiC differ morphologically, while their FIR spectra follow a similar λ -1.4 trend. Astronomical observations at these long wavelengths do not allow any identification of the actual SiC type existing in space which, on the contrary, can probably be identified by analysing the 11.5 μm band.

Carbonaceous materials as components of cometary dust

Abstract Recent exploration of comet Halley by space missions and ground-based observations have allowed to acquire a large amount of new information on cometary materials. In particular, IR spectroscopy has evidenced two pronounced and structured emission features at around 3.28 and 3.37 μm. Different kinds of gaseous molecules and/or solid grains including CH-X bonds have been proposed as possible carriers of the bands. In the past years, laboratory experiments have allowed to characterize the physical and optical properties of different classes of carbonaceous materials. The absorption properties measured for some of them are here used to fit the cometary features and to identify - if possible - the most probable carriers of these bands.

Laboratory measurements of physical properties on submicronic particles candidate as cosmic dust

SummaryWe present here a compendium of our laboratory measurements of the physical properties of submicronic particles of materials candidate as cosmic dust: amorphous carbon, silicon carbide and graphite. Comparison with data obtained by other authors is presented and discussed in view of astrophysical applications.RiassuntoSi riporta un compendio dei risultati sperimentali ottenuti nel nostro laboratorio, sulle proprietà fisiche e morfologiche di grani di dimensioni submicroniche di materiali carbonacei (carbone amorfo, carburo di silicio, grafite), candidati quali polveri cosmiche. I nostri dati sono confrontati con risultati di altri autori e sono discussi nella prospettiva di applicazioni astrofisiche.

Amorphous carbon and carbonaceous materials in space: I.—Laboratory measurements

SummaryWe present here the most recent measurements (UV and Raman spectroscopy) carried out on carbonaceous materials candidates as cosmic dust.RiassuntoIn questo lavoro vengono presentate le misure piú recenti (spettroscopia UV e Raman) effettuate su materiali carbonacei candidati come polvere cosmica.РезюмеВ этой работе приводятся результаты последних измерений (с помощью ультрафиолетовой и рамановской спектроскопии) на разиичных углеродистых материалах, как частицах космической пыли.

Silicon carbide in laboratory, in interstellar space and in the solar system

SummaryUsing theoretical models and our laboratory data on different dust mixtures containing silicon carbide grains, we obtained the best fit of several infrared emission spectra of carbon stars and comets. The results suggest that silicon carbide formed in the envelopes around carbon stars and also present in our solar system may provide an important link between interstellar and interplanetary solid material.