Knowledge of interstellar dust questioned with WIRCam and Herschel observations.

JHK WIRCam false-color images of the cores. Regions with minimal extinction used to calibrate the intrinsic color scatter in the background stars are outlined in green.

A team of astronomers from Canada, the United States, Germany and Chile using WiRCam at CFHT and the Herschel space telescope has found that dust models may need some reworking. They studied three isolated dust cores in molecular clouds and found that the properties of the cores could not completely account for their observations using state of the art dust modeling.

Dust is found everywhere in the universe and has to be accounted for when studying stars and galaxies. For example, dust will redden the light of a blue star and make it look red or obscure a region of space and make is look starless. However, it is not a trivial business to account for dust properties. It will absorb light chromatically meaning that the amount of light absorbed varies with color. Also dust emits light and can shine in the infrared or all the way down to submillimeter wavelength. The amount of emission or absorption of light by dust depends on the grains physical properties like size, composition, density and geometry. To top it off, dust properties are also influenced by their surroundings. For example, a nearby hot star will raise the temperature of the dust and will also affect its geometry. In short, dust is messy and difficult to model.

However, dust models are needed in the vast majority of astrophysical studies since dust affects almost every astronomical measurements. In a study aimed at assessing the reliability of such models, the team took WIRCAM images of dust cores in isolated molecular clouds and determined how much the dust in these clouds was blocking the light from background stars. They then compared these results with the far-infrared emission seen in the Herschel data by that same dust to see if the emission was consistent with that expected from dust models used in the literature. Though they found consistency between dust models and the observed absorption/emission, they surprisingly could not find a single model that was consistent for all three clouds. This indicates that the dust in the cores is not well described by any individual dust property model considered.

Refining dust models is an important task in Astrophysics. The results of this study has given pointers as to where to look to refine the models. In time, this will help astronomers have a better and more accurate measurements of the quantities that rely on dust models.

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Mary Beth Laychak
Outreach Manager
Canada-France-Hawaii Telescope

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Kristi Webb
University of Waterloo