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  1. Abstract

    Wide-field near-infrared (NIR) polarimetry was used to examine disk systems around two brown dwarfs (BDs) and two young stellar objects (YSOs) embedded in the Heiles Cloud 2 (HCl2) dark molecular cloud in Taurus as well as numerous stars located behind HCl2. Inclined disks exhibit intrinsic NIR polarization due to scattering of photospheric light, which is detectable even for unresolved systems. After removing polarization contributions from magnetically aligned dust in HCl2 determined from the background star information, significant intrinsic polarization was detected from the disk systems of one BD (ITG 17) and both YSOs (ITG 15, ITG 25), but not from the other BD (2M0444). The ITG 17 BD shows good agreement of the disk orientation inferred from the NIR and from published Atacama Large Millimeter/submillieter Array dust continuum imaging. ITG 17 was also found to reside in a 5200 au wide binary (or hierarchical quad star system) with the ITG 15 YSO disk system. The inferred disk orientations from the NIR for ITG 15 and ITG 17 are parallel to each other and perpendicular to the local magnetic field direction. The multiplicity of the system and the large BD disk nature could have resulted from formation in an environmentmore »characterized by misalignment of the magnetic field and the protostellar disks.

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  2. 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
  3. 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.
  4. 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