Astrophys. J., 875, 64-64 (2019/April-2)
Polarimetric and photometric investigation of the dark globule LDN 1225: distance, extinction law, and magnetic fields.
ESWARAIAH C., LAI S.-P., MA Y., PANDEY A.K., JOSE J., CHEN Z., SAMAL M.R., WANG J.-W., SHARMA S. and OJHA D.K.
Abstract (from CDS):
We present results based on the optical R-band observations of the polarization of 280 stars distributed toward the dark globule LDN 1225. Parallaxes from Gaia data release 2 along with the polarization data of ∼200 stars have been used to (a) constrain the distance of LDN 1225 as 830 ± 83 pc, (b) determine the contribution of interstellar polarization, and (c) characterize the dust properties and delineate the magnetic field (B-field) morphology of LDN 1225. We find that B-fields are more organized and exhibit a small dispersion of 12°. Using the 12CO molecular line data from the Purple Mountain Observatory, along with the column density and dispersion in B-fields, we estimate the B-field strength to be ∼56 ± 10 µG, the ratio of magnetic to turbulent pressure to be ∼3 ± 2, and the ratio of mass to magnetic flux (in units of the critical value) to be <1. These results indicate the dominant role of B-fields in comparison to turbulence and gravity in rendering the cloud support. B-fields are aligned parallel to the low-density parts (traced by a 12CO map) of the cloud; in contrast, they are neither parallel nor perpendicular to the high-density core structures (traced by 13CO and C18O maps). LDN 1225 hosts two 70 µm sources, which seem to be low-mass Class 0 sources. The ratio of total to selective extinction derived using optical and near-infrared photometric data is found to be anomalous (RV = 3.4), suggesting the growth of dust grains in LDN 1225. The polarization efficiency of dust grains follows a power law with an index of -0.7, implying that optical polarimetry traces B-fields in the outer parts of the cloud.
© 2019. The American Astronomical Society.
dust, extinction - ISM: clouds - local interstellar matter - magnetic fields - polarization
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