Near-infrared multiwavelength imaging polarimetry of the low-mass proto-stellar object HL Tauri

Abstract

We present the JHK-band high-resolution polarimetric images of the low-mass proto-stellar object HL Tau using the adaptive optics-equipped CIAO instrument on the Subaru telescope. Our polarization images show a butterfly-shaped polarization disk with an ∼09x 30 extension. In the nebula, where polarization vectors are centro-symmetrically aligned, the polarization is as high as P J ∼ 30%, P H ∼ 42%, and P K ∼ 55%. On the other hand, low polarizations of P < 3% in the J, H, and K bands and a low color excess ratio of E J-H /E H-K = 1.1 compared to the standard cloud value of 1.75 are detected towards the central star. We estimated the upper limit of the grain sizes a max to be 0.4 μm in the nebula and 0.7 μm in the line of sight towards the central star. Our high-resolution polarimetric data, which spatially resolves the polarization disk, provides us with important information about grain growth in the region close to the central star.