Study of magnetic field geometry and extinction in Bok globule CB130

Abstract

We trace the peripheral magnetic field structure of Bok globule CB130, by estimating the linear polarization of its field stars in the R band. The magnetic field orientation sampled by these stars, aligned on average among themselves and the polarization produced within the cloud has a different direction from that of Galactic plane with an offset of 53$^\circ$. The offset between minor axis and the mean magnetic field of CB130 is found to be 80$^\circ$. The estimated strength of the magnetic field in the plane-of-the-sky is $\sim$ 116$\pm$19 $\mu$G. We constructed the visual extinction map using Near Infrared Color Excess (NICE) method to see the dust distribution around CB130. Contours of Herschel {Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA} SPIRE 500$\mu$m dust continuum emission maps of this cloud is over-plotted on the visual extinction map which shows the regions having higher optical extinction corresponds to higher densities of dust. Three distinct high dust density cores (named as C1, C2, and C3) are identified in the extinction map. It is observed that the cores C1 and C3 located close to two previously known cores CB130-1 and CB130-2 respectively. Estimate of visual extinction of some moderately obscured stars of CB130 are made utilizing near-infra red photometry. Its observed that there is a feeble dependence of polarization on extinction; and polarization efficiency (defined as $ \textit{p}$/A$ {V}$) of the dust grains decreases with the increase in extinction.