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2017ApJ...849..157W - Astrophys. J., 849, 157-157 (2017/November-2)

Multiwavelength stellar polarimetry of the filamentary cloud IC5146. I. Dust properties.


Abstract (from CDS):

We present optical and near-infrared stellar polarization observations toward the dark filamentary clouds associated with IC5146. The data allow us to investigate the dust properties (this paper) and the magnetic field structure (Paper II). A total of 2022 background stars were detected in the Rc, i , H, and/or K bands to AV 25 mag. The ratio of the polarization percentage at different wavelengths provides an estimate of λ{max}, the wavelength of the peak polarization, which is an indicator of the small-size cutoff of the grain size distribution. The grain size distribution seems to significantly change at AV∼3 mag, where both the average and dispersion of PRc/PH_ decrease. In addition, we found λ{max}∼0.6–0.9µm for AV 2.5 mag, which is larger than the ∼0.55 µm in the general interstellar medium (ISM), suggesting that grain growth has already started in low-AV regions. Our data also reveal that polarization efficiency (PE≡Pλ/AV) decreases with AV as a power law in the Rc, i , and K bands with indices of -0.71 ± 0.10, -1.23 ± 0.10, and -0.53 ± 0.09. However, H-band data show a power index change; the PE varies with AV steeply (index of -0.95 ± 0.30) when AV 2.88±0.67 mag, but softly (index of -0.25 ± 0.06) for greater AV values. The soft decay of PE in high-AV regions is consistent with the radiative alignment torque model, suggesting that our data trace the magnetic field to AV∼20 mag. Furthermore, the breakpoint found in the H band is similar to that for AV, where we found the PRc/PH_ dispersion significantly decreased. Therefore, the flat PE-AV in high-AV regions implies that the power-index changes result from additional grain growth.

Abstract Copyright: © 2017. The American Astronomical Society. All rights reserved.

Journal keyword(s): dust, extinction - ISM: clouds - ISM: individual objects: IC5146 - ISM: magnetic fields - ISM: structure - polarization - polarization

VizieR on-line data: <Available at CDS (J/ApJ/849/157): table1.dat>

Status in Simbad:  will not be processed

Simbad objects: 12

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