A Multicolor Study of Polarization Variability in Isolated B[e] Stars HD 45677 and HD 50138

Lai²,

et al. 2019

ApJ

Self Cite

We present the results based on the optical R-band polarization observations of 280 stars distributed towards the dark globule LDN 1225. Gaia data release 2 parallaxes along with the polarization data of ∼200 stars have been used to (a) constrain the distance of LDN 1225 as 830±83 pc, (b) determine the contribution of interstellar polarization (ISP), and (c) characterize the dust properties and delineate the magnetic field (B-field) morphology of LDN 1225. We find that B-fields are more organized and exhibit a small dispersion of 12 • . Using the 12 CO molecular line data from the Purple Mountain Observatory (PMO), along with the column density, dispersion in B-fields, we estimate B-field strength to be ∼56 ± 10 µG, magnetic to turbulence pressure to be ∼3 ± 2, and the mass-to-magnetic flux ratio (in units of critical value) to be < 1. These results indicate the dominant role of B-fields in comparison to turbulence and gravity in rendering the cloud support. B-fields are aligned parallel to the low-density parts (traced by 12 CO map) of the cloud, in contrast they are neither parallel nor perpendicular to the high-density core structures (traced by 13 CO and C 18 O maps). LDN 1225 hosts two 70 µm sources which seem to be of low-mass Class 0 sources. The total-to-selective extinction derived using optical and near-infrared photometric data is found to be anomalous (R V = 3.4), suggesting dust grain growth in LDN 1225. Polarization efficiency of dust grains follows a power-law index of −0.7 inferring that optical polarimetry traces B-fields in the outer parts of the cloud.

Section: Introductionsupporting

confidence: 81%

“…These values are considered as the ISP contribution. Similar methodology has been adopted to estimate the ISP contribution and retrieve the intrinsic polarizations of nearby clouds (eg., Eswaraiah et al 2013;Neha et al 2018), B[e] stars (eg., Lee et al 2018), and Supernova (Kumar, B., et al under review).…”

Section: Foreground Interstellar Polarization (Isp)mentioning

confidence: 99%

Polarimetric and Photometric Investigation of the Dark Globule LDN 1225: Distance, Extinction Law, and Magnetic Fields

Lai²,

et al. 2019

ApJ

Self Cite

“…The corresponding Q IS P and U IS P values are 0.032 ± 0.018 and -0.170 ± 0.019 per cent which are subtracted from the observed SN polarization measurements (see Section 3.4). A similar methodology has been used to derive the ISP contribution in dark globules and B[e] stars (Lee et al 2018;Eswaraiah et al 2019).…”

Section: Interstellar Polarizationmentioning

confidence: 99%

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

Kumar

Monthly Notices of the Royal Astronomical Society

Singh

et al. 2019

We present the results based on photometric (Swift UVOT), broad-band polarimetric (V and R-band) and optical spectroscopic observations of the Type IIn supernova (SN) 2017hcc. Our study is supplemented with spectropolarimetric data available in literature for this event. The post-peak light curve evolution is slow (∼ 0.2 mag 100 d −1 in b-band). The spectrum of ∼ +27 d shows a blue continuum with narrow emission lines, typical of a Type IIn SN. Archival polarization data along with the Gaia DR2 distances have been utilized to evaluate the interstellar polarization (ISP) towards the SN direction which is found to be P IS P = 0.17 ± 0.02 per cent and θ IS P = 140 • ± 3 • . To extract the intrinsic polarization of SN 2017hcc, both the observed and the literature polarization measurements were corrected for ISP. We noticed a significant decline of ∼ 3.5 per cent (V-band) in the intrinsic level of polarization spanning a period of ∼ 2 months. In contrast, the intrinsic polarization angles remain nearly constant at all epochs. Our study indicates a substantial variation in the degree of asymmetry in either the ejecta and/or the surrounding medium of SN 2017hcc. We also estimate a mass-loss rate oḟ M = 0.12 M yr −1 (for v w = 20 km s −1 ) which suggests that the progenitor of SN 2017hcc is most likely a Luminous Blue Variable.

Revealing the dust grain polarization properties as a function of extinction and distance towards NGC 1893

Bijas

Monthly Notices of the Royal Astronomical Society

Wang

et al. 2022

Dust polarization observations at optical wavelengths help us to understand the dust grain properties and trace the plane-of-the-sky component of the magnetic field. In this study, we make use of the I-band polarization data acquired from AIMPOL along with the distances (d) and extinction (AV) data to study the variation of polarization fraction (P) as a function of AV and d towards the star-forming region, NGC 1893. We employ a broken power-law fit and Bayesian analysis on extinction (AV) versus polarization efficiency (P/AV) and distance (d) versus rate of polarization (P/d). We find that P/AV shows a break at an extinction of ∼0.9 mag, whereas P/d exhibits a break at a distance of ∼1.5 kpc. Based on these, we categorize the dust towards NGC 1893 into two populations: (i) foreground dust confined to AV < ∼1 mag and distance up to ∼2 kpc and (ii) Perseus spiral arm dust towards NGC 1893 characterized with AV > ∼1 mag and distance beyond ∼2 kpc. Foreground dust exhibits higher polarization efficiency but a lower polarization rate, whereas Perseus dust shows a lower polarization efficiency but a slightly higher polarization rate. Hence, we suggest that while polarization efficiency reveals the dust grain alignment, the rate of polarization infers about the distribution of dust grains towards NGC 1893. Further, we also shed a light on the spatial variation of intrinsic polarization and magnetic field orientation, and other parameters within the intracluster medium of NGC 1893.