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    ABSTRACT: We report spatially resolved variations in the 3.4-mum hydrocarbon absorption feature and the 3.3-mum polycyclic aromatic hydrocarbon (PAH) emission band in the Circinus galaxy over the central few arcsec. The absorption is measured towards warm emitting dust associated with Coronal line regions to the east and west of the nucleus. There is an absorption optical depth tau3.4mum ~ 0.1 in the core which decreases to the west and increases to the east. This is consistent with increased extinction out to ~40 pc east of the core, supported by the Coronal emission line intensities which are significantly lower to the east than the west. PAH emission is measured to be symmetrically distributed out to +/-4 arcsec, outside the differential extinction region. The asymmetry in the 3.4-mum absorption band reflects that seen in the 9.7-mum silicate absorption band reported by Roche et al., and the ratio of the two absorption depths remains approximately constant across the central regions, with tau3.4mum/tau9.7mum ~ 0.06 +/- 0.01. This indicates well-mixed hydrocarbon and silicate dust populations, with no evidence for significant changes near the nucleus.
    Monthly Notices of the Royal Astronomical Society 01/2009; 394:2043-2049. · 5.52 Impact Factor
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    ABSTRACT: We analyze dust features present in the mid-infrared (Spitzer) and recently published L-band (UKIRT) spectra of the infrared galaxy IRAS 08572+3915. The line of sight toward the AGN nucleus crosses a high column density of carbonaceous dust whose characteristic absorption features appear clearly. They provide a real insight into the chemical environment of the diffuse interstellar medium. Thanks to the moderate redshift of IRAS 08572+3915, the wavelength of the aromatic CH stretching mode is free of major telluric lines, and a strong observational constraint of H$_{\rm sp2} $/H$_{\rm sp3} \le 0.08$ has been determined. This limit clearly shows that the bonding of hydrogen atoms in interstellar hydrogenated amorphous carbon is highly aliphatic. The presence of a broad absorption feature centered at 6.2 $\mu$m, probably arising from olefinic/aromatic structures, corresponds to the backbone of this carbonaceous material, which is the major carbon-containing component of the interstellar medium along this line of sight.
    Astronomy and Astrophysics 01/2007; · 5.08 Impact Factor
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    ABSTRACT: Aims: We search for frozen water and its processing around young stellar objects (YSOs of class I/II). We try to detect potential, regional differences in water ice evolution within YSOs, which is relevant to understanding the chemical structure of the progenitors of protoplanetary systems and the evolution of solid materials. Water plays an important role as a reaction bed for rich chemistry and is an indispensable requirement for life as known on Earth. Methods: We present our analysis of NAOS-CONICA/VLT spectroscopy of water ice at 3 mum for the T Tauri star YLW 16 A in the rho Ophiuchi molecular cloud. We obtained spectra for different regions of the circumstellar environment. The observed absorption profiles are deconvolved with the mass extinction profiles of amorphous and crystallized ice measured in laboratory. We take into account both absorption and scattering by ice grains. Results: Water ice in YLW16A is detected with optical depths of between tau = 1.8 and tau = 2.5. The profiles that are measured can be fitted predominantly by the extinction profiles of small grains (0.1 mum-0.3 mum) with a small contribution from large grains (
    Astronomy and Astrophysics 01/2010; · 5.08 Impact Factor

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