Abstract:
Aims. We aim to map the magnetic field geometry and to study the dust properties of the starless cloud, L1570, using multi-wavelength
optical polarimetry and photometry of the stars projected on the cloud.
Methods. The direction of the magnetic field component parallel to the plane of the sky of a cloud can be obtained using polarimetry
of the stars projected on and located behind the cloud. It is believed that the unpolarized light from the stars background to the cloud
undergoes selective extinction while passing through non-spherical dust grains that are aligned with their minor axes parallel to the
cloud magnetic field. The emerging light becomes partially plane polarized. The observed polarization vectors trace the direction of
the projected magnetic field of the cloud. We made R-band imaging polarimetry of the stars projected on a cloud, L1570, to trace the
magnetic field orientation. We also made multi-wavelength polarimetric and photometric observations to constrain the properties of
dust in L1570.
Results. We estimated a distance of 394 ± 70 pc to the cloud using 2MASS JHKs colors. Using the values of the Serkowski parame-
ters, σ₁ ,є¯, λmax , and the position of the stars on the near-infrared color–color diagram, we identified 13 stars that could possibly have
intrinsic polarization and/or rotation in their polarization angles. One star, 2MASS J06075075+1934177, which is a B4Ve spectral
type, shows diffuse interstellar bands in the spectrum in addition to the Hα line in emission. There is an indication for slightly bigger
dust grains toward L1570 on the basis of the dust grain size-indicators such as λmax and RV values. The magnetic field lines are found
to be parallel to the cloud structures seen in the 250 μm images (also in the 8 μm and 12 μm shadow images) of L1570. Based on
the magnetic field geometry, the cloud structure, and the complex velocity structure, we conclude that L1570 is in the process of
formation due to the converging flow material mediated by the magnetic field lines. A structure function analysis showed that in the
L1570 cloud region the large-scale magnetic fields are stronger than the turbulent component of the magnetic fields. The estimated
magnetic field strengths suggest that the L1570 cloud region is subcritical and hence could be strongly supported by the magnetic
field lines.
