Abstract
Abstract The relationship between dust polarization and extinction was determined for the cold dense starless molecular cloud core FeSt 1-457 based on the background star polarimetry of dichroic extinction at near-infrared wavelengths. Owing to the known (three-dimensional) magnetic field structure, the observed polarizations from the core were corrected by considering (a) the subtraction of the ambient polarization component, (b) the depolarization effect of inclined distorted magnetic fields, and (c) the magnetic inclination angle of the core. After these corrections, a linear relationship between polarization and extinction was obtained for the core in the range up to A V ≈ 20 mag. The initial polarization versus extinction diagram changed dramatically after the corrections of (a) to (c), with the correlation coefficient being refined from 0.71 to 0.79. These corrections should affect the theoretical interpretation of the observational data. The slope of the finally obtained polarization–extinction relationship is , which is close to the statistically estimated upper limit of the interstellar polarization efficiency. This consistency suggests that the upper limit of interstellar polarization efficiency might be determined by the observational viewing angle toward polarized astronomical objects.
Highlights
The relationship between dust dichroic polarization (P) and extinction (A) in molecular clouds and cores is important for two perspectives
The linearity in the P–A relationship confirms the interpretation of the observed interstellar polarization angle, which is closely related to the direction of magnetic fields pervading the line-of-sight region
Goodman et al (1995) proposed that the polarizing power of dust grains decreases inside cold dense dark molecular clouds
Summary
The relationship between dust dichroic polarization (P) and extinction (A) in molecular clouds and cores is important for two perspectives. Superposition of ambient polarizations in the same line of sight but unrelated to the core, (3) depolarization caused by the distorted magnetic fields of the core, and (4) the line-of-sight inclination angle of the magnetic axis of the core The latter three effects are measured and corrected to determine an accurate P–A relationship for this well-defined starless core. Comparing the model parabolic field with observations shows that the line-of-sight inclination angle of the magnetic field direction (magnetic axis) of the core is 45° ± 10° with a magnetic curvature C of. The depolarization effect as well as inclination in the magnetic axis modify the observed polarization vectors from their original vector values These effects can be corrected by using a 3D model and the best-fit parameters for FeSt 1-457
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