Interstellar Polarization Around the Bok Globule CB67

Abstract

Original polarimetric data of stars in the vicinity of the Bok globule CB67, located at the periphery of the nearby star-forming region ρ Oph, are considered. Variations of the visual extinction A_V in the plane of the sky and with distance d are analyzed using various data sources. It is found that a jump in A_V of about 0^m.8 at a distance of d ≈ 140 pc is associated with the neutral wind of the Upper Scorpius part of the Sco–Cen OB association. In the outer layers of CB67 (d = 140 pc), this jump increases by more than 0^m.5–1. The derived parameters of interstellar polarization for 66 stars around CB67 are supplemented with modern data on their distances and interstellar extinction. It is found that the magnetic-field direction in the immediate vicinity (several arcminutes) of CB67 has a position angle θ_B = 90 ± 20°, which differs significantly from the mean orientation in a wider (several-degree) region, where \(\overline{\uptheta }\) ≈ 60° . It is noted that for CB67 the value of θ_B agrees better than \(\overline{\uptheta }\) with the usual correlations between the magnetic-field (polarization) direction and the directions of maximum elongation of clouds and their rotation axes. For CB67, the latter are characterized by θ_L ≈ 107° and θ_R = 112°, respectively. With the exception of a few stars, the observed degree of polarization P correlates fairly well with A_V, and the obtained ratios P/A_V = 0.5–2%/mag are typical of the diffuse interstellar medium.