Broad-band linear polarization in late-type active FGK dwarfs


Polarimetric observations of stars in the sample were obtained during the years 2010–2014 using ARIES Imaging Polarimeter (AIMPOL; Rautela, Joshi & Pandey 2004) mounted at the Cassegrain focus of the 104 cm Sampurnanand telescope of the Aryabhatta Research Institute of Observational Sciences, Nainital, India, coupled with a 1024 × 1024 CCD camera. AIMPOL consists of a half-wave plate (HWP) modulator and a Wollaston prism beam-splitter. Each pixel of the CCD corresponds to 1.73 arcsec and the field of view is ∼ 8 arcmin in diameter.


The above figure shows the plot between normalized Stokes parameters Q and U have been shown. The

values of normalized Stokes parameters are concentrated near the origin (0,0) of the Q–U graph. However, the stars V526 Aur, V1658, Aql and V1659 Aql denoted by squares are located away from the origin indicating external sources of polarization.


The majority of stars in our sample are nearby and suffer negligible reddening. Therefore, it is natural to suppose that polarization due to Interstellar medium (ISM) may be negligible. However, three stars namely V526 Aur, V1658 Aql and V1659 Aql are located at a distance more than 300 pc and may have suffered considerable reddening indicating that observed polarization may be due to the foreground ISM. Further, in order to explore possibilities of ISM polarization, the average values of polarization are fitted to the standard Serkowski’s polarization law (Serkowski, Mathewson & Ford 1975).

[Image Credit: Patel, Pandey, & Karmakar et al. (2016)]