Smoke in the Pipe Nebula: dust emission and grain growth in starless cores
Using a novel combination of submillimeter dust emission maps from both Herschel and APEX-Laboca and near-infrared dust extinction measurements, we constrain the dust opacity in starless cores in the Pipe Nebula. Such observations are particularly interesting because they can directly yield signatures of dust grain growth. In the first step, we use a combination of dust emission and extinction measures to determine the behaviour of the submilllimeter dust opacity in starless cores. In a second step, we use a dust spectral energy distribution model derived from Herschel data and compare it against independent APEX-Laboca measurements, thereby directly obtaining information on the dust opacity spectral index beta. This second step is designed in a way not to depend on any zeropoint offset between the two datasets, as occurs from spatial filtering on scales larger then the cores. We apply this methodology to the starless dense core FeSt 1-457, and we find 1) evidence for an increased submillimeter dust opacity toward the center of this core, and 2) no evidence for beta changes inside the core. These results confirm theoretical expectations of grain growth. We will discuss the implications and provide an outlook of using this methodology on a larger sample of cores for which the required multi-wavelength data is already available.