5,150 research outputs found
The role of the charge state of PAHs in ultraviolet extinction
Aims: We explore the relation between charge state of polycyclic aromatic
hydrocarbons (PAHs) and extinction curve morphology. Methods: We fit extinction
curves with a dust model including core-mantle spherical particles of mixed
chemical composition (silicate core, and carbonaceous layers),
and an additional molecular component. We use exact methods to calculate the
extinction due to classical particles and accurate computed absorption spectra
of PAHs in different charge states, for the contribution due to the molecular
component, along a sample of five rather different lines of sight. Results: A
combination of classical dust particles and mixtures of real PAHs
satisfactorily matches the observed interstellar extinction curves. Variations
of the spectral properties of PAHs in different charge states produce changes
consistent with the varying relative strengths of the bump and non-linear
far-UV rise.Comment: 5 pages, 3 figures, Astronomy & Astrophysics Letters, in pres
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A new CO carbonaceous chondrite from Acfer, Algeria
Many small fragments, totally weighing 118 g were found in the Acfer area by an Italian dealer. Chondrules size and types (predominance of granular olivine type), occurrence of twinned clinoenstatite and absence of plagioclase suggested a classification as CO carbonaceous chondrite
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A new CK carbonaceous chondrite from Hammada Al Hamra, Libya
A single stone weighing 198 g was found in 2001 in the Hammada al Hamra region of Libya. Petrographic features (mean chondrules dimensions, coarse grained matrix and presence of AOIs and CAIs) point to a classification as CK carbonaceous chondrite
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A new CH carbonaceous chondrite from Acfer, Algeria
A single stone weighing 1456 g was found in November 2002 in the Acfer area, Algeria. Oxygen isotope, chondrules-matrix ratio as well as other petrographic features point to a classification as CH carbonaceous chondrite
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Textural and compositional features of NWA 4222, A new Martian meteorite
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