Day 729

Monday.

1408.5133
On the radiation driven alignment of dust grains: detection of the polarization hole in a starless core
Alves, et al

Investigate the polarization properties of a starless core in a very early evolutionary stage.  Linear polarization data reveal the properties of the dust grains in the distinct phases of the ISM.  The goal is to investigate how the polarization degree and angle correlate with the cloud and core gas.  Use optical, NIR and sub millimeter polarization observations toward the starless object Pipe-109 in the Pipe nebula.  Data cover a physical scale range of 0.08 to 0.4 pc, comprising the dense gas, envelope and the surrounding cloud.  The cloud polarization is well traced by the optical data.  The NIR polarization is produced by a mixed population of grains from the core border and the cloud gas.  The optical and NIR polarization toward the cloud reach the maximum possible value and saturate wrt the visual extinction.  Modeling of the sub millimeter polarization indicate a magnetic field main direction projected onto the plane-of-sky and loss of grain alignment for densities higher than 6e4 cm^-3 (or A_V>30 mag).  Pipe-109 is immersed in a magnetized medium, with a very ordered magnetic field.  The absence of the internal source of radiation significantly affects the polarization efficiencies in the core, creating a polarization hole at the center of the starless core.  This result supports the theory of dust grain alignment via radiative torques.

1408.5143
Next generation strong lensing time delay estimation with Gaussian processes
Hojjati, Linder

SL forms multiple, time delayed images of cosmological sources, with the "focal length" of the lens serving as a cosmological distance probe.  Robust estimation of the time delay distance can tightly constrain the Hubble constant as well as the matter density and DE.  Current and next generation surveys will find hundreds to thousands of lensed systems but accurate time delay estimation from noisy, gappy light curves is potentially a limiting systematic.  Using a large sample of blinded light curves from the SL TD challenge, develop and demonstrate a Gaussian Process cross correlation technique that delivers an average bias within 0.1% depending on the sampling, necessary for sub percent Hubble constant determination.  The fits are accurate (80% of them within 1 day) for delays from 5-100 days and robust against cadence variations shorted than 6 days.  Study the effects of survey characteristics such as cadence, season, and campaign length, and derive requirements for time delay cosmology: in order not to bias the cosmology determination by 0.5 sigma, the mean time delay fit accuracy must be better than 0.2%.