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  1. The orientation of the magnetic field (B field) in the filamentary dark cloud GF 9 was traced from the periphery of the cloud into the L1082C dense core that contains the low-mass, low-luminosity Class 0 young stellar object (YSO) GF 9-2 (IRAS 20503+6006). This was done using SOFIA HAWC+ dust thermal emission polarimetry (TEP) at 216 μm in combination with Mimir near-infrared background starlight polarimetry (BSP) conducted in the H band (1.6 μm) and K band (2.2 μm). These observations were augmented with published I-band (0.77 μm) BSP and Planck 850 μm TEP to probe B-field orientations with offset from the YSO in a range spanning 6000 au to 3 pc. No strong B-field orientation change with offset was found, indicating remarkable uniformity of the B-field from the cloud edge to the YSO environs. This finding disagrees with weak-field models of cloud core and YSO formation. The continuity of inferred B-field orientations for both TEP and BSP probes is strong evidence that both are sampling a common B field that uniformly threads the cloud, core, and YSO region. Bayesian analysis of Gaia DR2 stars matched to the Mimir BSP stars finds a distance to GF 9 of 270 ± 10more »pc. No strong wavelength dependence of B-field orientation angle was found, contrary to previous claims.« less
  2. A faint star located 2 arcsec from KIC 8462852 was discovered in Keck 10 m adaptive optics imaging in the JHK near-infrared (NIR) in 2014 by Boyajian et al. (2016). The closeness of the star to KIC 8462852 suggested that the two could constitute a binary, which might have implications for the cause of the brightness dips seen by Kepler and in ground-based optical studies. Here, NIR imaging in 2017 using the Mimir instrument resolved the pair and enabled measuring their separation. The faint star had moved 67 ± 7 milliarcsec (mas) relative to KIC 8462852 since 2014. The relative proper motion of the faint star is 23.9 ± 2.6 mas yr-1, for a tangential velocity of 45 ± 5 km s-1 if it is at the same 390 pc distance as KIC 8462852. Circular velocity at the 750 au current projected separation is 1.5 km s-1, hence the star pair cannot be bound.
  3. 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 R c , I\prime , H, and/or K bands to {A}V≲ 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 {A}V˜ 3 mag, where both the average and dispersion of {P}{Rc}/{P}H decrease. In addition, we found {λ }\max ˜ 0.6{--}0.9 μm for {A}V> 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-A V regions. Our data also reveal that polarization efficiency ({PE}\equiv {P}λ /{A}V) decreases with A V as a power law in the R c , I\prime , 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; themore »PE varies with A V steeply (index of -0.95 ± 0.30) when {A}V< 2.88+/- 0.67 mag, but softly (index of -0.25 ± 0.06) for greater A V values. The soft decay of PE in high-A V regions is consistent with the radiative alignment torque model, suggesting that our data trace the magnetic field to {A}V˜ 20 mag. Furthermore, the breakpoint found in the H band is similar to that for A V , where we found the {P}{Rc}/{P}H dispersion significantly decreased. Therefore, the flat PE-A V in high-A V regions implies that the power-index changes result from additional grain growth.« less