Distortion of Magnetic Fields in a Starless Core III: Polarization--Extinction Relationship in FeSt 1-457

TL;DR

This study investigates the polarization-extinction relationship in the starless core FeSt 1-457, correcting for magnetic field effects to better understand dust polarization efficiency and its implications for interstellar magnetic field studies.

Contribution

The paper introduces a method to correct polarization data for magnetic field distortions, revealing a more accurate linear polarization-extinction relationship in a dense core.

Findings

Corrected polarization-extinction relationship with a correlation coefficient of 0.79.

The slope of the relationship is close to the interstellar polarization efficiency upper limit.

Results suggest observational viewing angles influence polarization efficiency limits.

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 $A_V \approx 20$ mag. The initial polarization vs. 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 $P_H / E_{H-K_s} = 11.00 \pm 0.72$ $\%$ ${\rm mag}^{-1}$, which is close to the statistically estimated upper limit of the interstellar polarization efficiency (Jones 1989). This consistency suggests that the upper limit of interstellar polarization efficiency might be determined by the observational viewing angle toward polarized astronomical objects.