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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: Over the last decade, we have made great strides in better understanding dust composition and evolution in dense clouds and the diffuse interstellar medium (ISM). Thanks to improvements in IR detector sensitivity on ground-based telescopes and the Spitzer Space Telescope mission, we are no longer limited to a handful of bright background stars in order to study dust composition in quiescent dense clouds and the diffuse ISM. More thorough sampling of lines of sight in these regions has highlighted the dichotomy of the nature and composition of dust in these environments. In addition, successes in recreating interstellar processes and dust-analogs in the laboratory have helped us to understand the differences in dust absorption features we observe in the ISM. In this article, we focus on the organic components of interstellar dust, reviewing past work and highlighting the most recent observations and laboratory experiments.
    Proceedings of the International Astronomical Union 01/2008; 4:35 - 44.
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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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