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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: We present measurements of the 3.4-μm hydrocarbon dust absorption feature, and four visual diffuse interstellar bands, for 12 highly reddened [9.0 < A(V) < 15.8], early-type stars identified from the Stephenson catalogue, covering a range of Galactic longitude. The hydrocarbon feature is detected in 11 sightlines with optical depths of up to 0.05, and corresponding column densities are derived. The feature is weaker per unit A(V) than previously reported, further underlining earlier observations of its enhancement in the Galactic Centre. A comparison of the 3.4-μm feature substructure indicates organic material similar to that seen in earlier diffuse medium studies, suggesting a uniform formation history across the Galactic disc. The profile is well matched by both meteoritic material and several laboratory-prepared analogues. The diffuse interstellar bands (DIBs) measured were λλ6177, 6203, 6284 and 6614; no strong correlations were detected, either between these bands themselves or between the DIBs and the 3.4-μm feature, although λλ6284 and 6614 appear to vary together. If the carriers of the DIBs are organic and molecular in nature and have cosmic carbon abundance requirements similar to those of the C–H stretch, these results imply that there is little direct carbon exchange between them and the aliphatic dust component. Measurements of the extinction to these objects suggest luminosity anomalies similar to that already seen in Cyg OB2 no 12.
    Monthly Notices of the Royal Astronomical Society 05/2003; 341(4):1121 - 1140. · 5.52 Impact Factor

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