Bok globule CB 17: polarization, extinction and distance

Abstract

In this paper, the results obtained from the polarimetric study of a Bok globule CB17 in both optical and sub-millimeter wavelength are presented. The optical polarimetric observations in R-band (λ = 630 nm, ∆λ = 120 nm) were conducted from 1.04-meter Sampurnanand Telescope, ARIES, Nainital, India on 9th March 2016, while, the sub-mm polarimetric data are taken from the SCUPOL data archive which has been reanalyzed. The contours of Herschel ¶ SPIRE 500µm dust continuum emissions of CB17 (typically a cometary-shaped globule) are overlaid on the DSS image of CB17 along with polarization vectors (optical and submm). The magnetic field strength at the core of the globule is estimated to be 99µG. Using the Near-Infrared photometric technique and Gaia data, the distance to CB17 is found to be 253 ± 43 parsec. A correlation between the various quantities of the globule is also studied. It is observed that the magnetic field in the cloud core as revealed by polarization measurements at the sub-millimeter dust emission is found to be almost aligned along the minor axis of the globule which fits the magnetically regulated star formation model. The misalignment between core-scale magnetic field direction and molecular outflow direction is also found.

The Relative Orientation between Local Magnetic Field and Galactic Plane in Low Latitude Dark Clouds

“…So, the envelope magnetic field orientation is clearly aligned along the GP in both the clouds. A similar trend was observed for cloud CB17 by Choudhury et al (2019). In contrast, in the case of CB188, θ off = 70°.5 (Figure 3) though all the polarization vectors are unidirectional.…”

“…Several researchers studied the orientation of the magnetic field through imaging polarimetry (Chakraborty et al 2014;Soam et al 2015Soam et al , 2017Chakraborty & Das 2016;Das et al 2016;Jorquera & Bertrang 2018;Choudhury et al 2019;Zielinski et al 2021) and discussed the relative orientation of the magnetic field to the galactic plane (GP), outflow direction and minor axis of the cloud. The optical polarimetric analysis reveals that the envelope magnetic field of CB130 is oriented at an angle of 53°with respect to the orientation of GP (Chakraborty & Das 2016).…”

“…They presented the relative orientation of the envelope magnetic field with the minor axis of the cloud for both the cores, which supports magnetically dominated star formation models. Analyzing both optical and sub-mm polarimetric data of Bok globule CB17, Choudhury et al (2019) reported a parallel alignment between the envelope magnetic field and the position angle of GP in contrast to the core-scale magnetic field, which is almost perpendicular to the GP. They also reported a relative orientation envelope magnetic field to the outflow axis and the cloud minor axis.…”

The JCMT BISTRO Survey: The Distribution of Magnetic Field Strengths toward the OMC-1 Region

“…where B pos is the magnetic field strength in the plane of the sky in units of microgauss; Q is a correction factor, which is suggested to be 0.5 by Ostriker et al (2001); ρ is the mean volume density in g cm −3 ; σ v is the nonthermal velocity dispersion of the gas in km s −1 ; σ θ is the dispersion of polarization angles in degrees; ρ = μm H n(H 2 ), where μ = 2.8 is the mean molecular weight per particle by assuming 10% of total gas number is helium (Kauffmann et al 2008) and m H is the mass of a hydrogen atom; n(H 2 ) is the volume density of molecular hydrogen in units of cm −3 ; and ΔV is the FWHM of the nonthermal component of a spectral line in units of km s −1 . A dispersion of polarization angles is often measured as a standard deviation of the angles assuming that an underlying magnetic field is uniform with a direction equal to the mean orientation of the polarization segments over quite a large area, or the whole area, of a molecular cloud or core (e.g., Kirk et al 2006;Curran & Chrysostomou 2007;Cortes et al 2016;Choudhury et al 2019). Other methods include a nonuniform magnetic field model to fit the overall shape of polarization segments (Girart et al 2009), a two-point correlation function to determine the field structure function (e.g., Hildebrand et al 2009;Houde et al 2009;Poidevin et al 2010;Chuss et al 2019), and a spatial filter to estimate the underlying field morphology (Pillai et al 2015).…”

The JCMT BISTRO Survey: The Distribution of Magnetic Field Strengths towards the OMC-1 Region

“…where B pos is magnetic field strength in the plane of the sky in units of µG; Q is a correction factor which is suggested as 0.5 by Ostriker et al (2001); ρ is the mean volume density in g cm −3 ; σ v is the non-thermal velocity dispersion of the gas in km s −1 ; σ θ is the dispersion of polarization angles in degrees; ρ = µm H n(H 2 ), where µ=2.8 is the mean molecular weight per particle by assuming 10% of total gas number is helium (Kauffmann et al 2008) and m H is the mass of a hydrogen atom; n(H 2 ) is the volume density of molecular hydrogen in units of cm −3 ; ∆V is the full width at half maximum (FWHM) of the non-thermal component of a spectral line in units of km s −1 . A dispersion of polarization angles is often measured as a standard deviation of the angles assuming that an underlying magnetic field is uniform with a direction equal to the mean orientation of the polarization segments over quite a large area of, or the whole area of, a molecular cloud or core (e.g., Kirk et al 2006;Curran & Chrysostomou 2007;Cortes et al 2016;Choudhury et al 2019). Other methods include a non-uniform magnetic field model to fit the overall shape of polarization segments (Girart et al 2009), a two-point correlation function to determine the field structure function (e.g., Hildebrand et al 2009;Houde et al 2009;Poidevin et al 2010;Chuss et al 2019), and a spatial-filter to estimate the underlying field morphology (Pillai et al 2015).…”