Polarimetric and photometric investigation of a dark globule LDN 1225:
  distance, extinction law, and magnetic fields
  We present the results based on the optical $R$-band polarization
observations of 280 stars distributed towards the dark globule LDN\,1225. {\it
Gaia} data release 2 parallaxes along with the polarization data of $\sim$200
stars have been used to (a) constrain the distance of LDN\,1225 as
830$\pm$83~pc, (b) determine the contribution of interstellar polarization
(ISP), and (c) characterize the dust properties and delineate the magnetic
field (B-field) morphology of LDN\,1225. We find that B-fields are more
organized and exhibit a small dispersion of 12$\degr$. Using the $^{12}$CO
molecular line data from the Purple Mountain Observatory (PMO), along with the
column density, dispersion in B-fields, we estimate B-field strength to be
$\sim$56\,$\pm$\,10\,$\mu$G, magnetic to turbulence pressure to be
$\sim$3\,$\pm$\,2, and the mass-to-magnetic flux ratio (in units of critical
value) to be~$<$\,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 $^{12}$CO map) of the
cloud, in contrast they are neither parallel nor perpendicular to the
high-density core structures (traced by $^{13}$CO and C$^{18}$O maps).
LDN\,1225 hosts two 70\,$\mu$m sources which seem to be of low-mass Class 0
sources. The total-to-selective extinction derived using optical and
near-infrared photometric data is found to be anomalous ($R_{V}$~$=$~3.4),
suggesting dust grain growth in LDN\,1225. Polarization efficiency of dust
grains follows a power-law index of $-$0.7 inferring that optical polarimetry
traces B-fields in the outer parts of the cloud.
