A Multiband Optical Polarimetric Study of Classical Be Stars with Exceptionally Large Near-Infrared Excess

摘要

Polarimetric technique is an efficient tool to study the dust properties not only in the interstellar and intra-cluster medium, but also in circumstellar environments.We present new multiband(BV(RI)C) optical polarimetric observations of six classical Be stars, HD259431, HD62532, HD45677,HD50138, BD+56 563 and BD+56 573, to diagnose the presence of dust in their circumstellar environments. The foreground dust distribution shows the presence of dust layers at distances of ～ 200-500 pc. Five stars show an indication of possible intrinsic polarization and (or) rotation in their polarization angles. Especially, two stars HD45677 and HD50138, which show relatively large near-infrared excess with both (J-H) and (H-K) > 0.7 mag, exhibit more polarization at shorter wavelengths than that at longer wavelengths thereby indicating the presence of small dust grains in their circumstellar disk/envelope. Four stars namely HD259431, HD62532, HD45677 and HD50138 show a significant amount of intrinsic polarization indicating the presence of copious amount of dust in an asymmetric distribution e.g., in the form of disk or toroid. In the case of two CBe stars (BD+56 563 & BD+56 573) which are located in the star cluster χ Per, the observed polarization of these two stars seems to dominated by the foreground dust polarization.