ﻻ يوجد ملخص باللغة العربية
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, $sp^2$ and $sp^3$ 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.
We have obtained new STIS/HST spectra to search for structure in the ultraviolet interstellar extinction curve, with particular emphasis on a search for absorption features produced by polycyclic aromatic hydrocarbons (PAHs). The presence of these mo
Interstellar extinction in ultraviolet is the most severe in comparison with optical and infrared wavebands and a precise determination plays an important role in correctly recovering the ultraviolet brightness and colors of objects. By finding the o
The M82 galaxy has been the subject of several studies basically because it is relatively close to to the Milky Way and it displays a strong star formation activity. Using multi-band images of M82 we have determined the age and extinction of the stel
While all but one Gamma-Ray Bursts observed in the X-ray band showed an X-ray afterglow, about 60 per cent of them have not been detected in the optical band. We demonstrate that in many cases this is not due to adverse observing conditions, or delay
Recent investigation of the extinction law in 30 Dor and the Tarantula Nebula, at optical and near infrared (NIR) wavelengths, has revealed a ratio of total to selective extinction R_V=A_V/E(B-V) of about 4.5. This indicates a larger fraction of big