A study of the starless dark cloud LDN 1570: Distance, dust properties, and magnetic field geometry

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 JHK s colors. Using the values of the Serkowski parameters, σ 1 , , λ max , 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 λ max and R V 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.

Photometric and polarimetric observations of fast declining Type II supernovae 2013hj and 2014G

“…For the polarized standards, the degree of polarization P measured from the instrument is found consistent within limit of errors and any offset found in the measured and standard values of polarization angle θ is corrected in the measurements for SNe. Using unpolarized standards, the instrumental polarization is found to vary within 0.03 to 0.10%, which is consistent to that found by other authors for AIMPOL (see e.g., Rautela et al 2004;Eswaraiah et al 2013). Since the direction of polarization is not confined to any particular plane and the value itself is very small (within error limits), we have not subtracted this from our observational measurements.…”

Broad-band polarimetric investigation of the Type II-plateau supernova 2013ej

“…Nevertheless, the SN was observed slightly off-axis which yielded simultaneous imaging of few field stars along with the SN (see also Section 3.1.1). The instrumental polarization of AIMPOL on the 104 cm ST has been characterized and monitored since 2004 for different projects and generally found to be ∼0.1 per cent in R c -band (e.g., Rautela et al, 2004;Pandey et al, 2009;Eswaraiah et al, 2011Eswaraiah et al, , 2013Kumar et al, 2014;Soam et al, 2015, and references therein). To verify this result, we further observed unpolarized standards stars G 191 B2B and HD 21447 from Schmidt, Elston & Lupie (1992) on different nights and their degree of polarization was estimated to be 0.13 ± 0.03 and 0.14 ± 0.05 per cent, respectively.…”

On the observational behaviour of the highly polarized Type IIn supernova SN 2017hcc

“…The instrumental polarization of AIMPOL is generally found to be small, at ∼ 0.1 per cent (see, e.g. Medhi et al 2007;Pandey et al 2009;Das et al 2013;Eswaraiah et al 2012Eswaraiah et al , 2013Patel et al 2013;Soam et al 2015;Neha et al 2016;Rakshit et al 2017;Wang et al 2017;Lee et al 2018, and references therein). This was verified by the observations of the unpolarized standard star HD 12021 (Schmidt, Elston & Lupie 1992).…”