Near-infrared imaging polarimetry of bipolar nebulae. 4: GL-490, GL-2789, GL-2136

Abstract

High spatial resolution near-IR polarization and surface brightness images of the ouflow sources GL 490, GL 2789 and GL 2136 are presented. Polarization vector-maps at J, H and K show centro-symmetric patterns around GL 490, GL 2789 (NO) and GL 2136, indicating they are illuminating near-IR reflection nebulae. The J,H and K surface brightness images of GL 2789 reveal an arc-like feature (NI) to the north-west of the outflow source (NO). This is interpreted as a slab of material, swept-up by the blueshifted outflow from GL 2789 (NO) and illuminated by GL 2789 (NO) at near-IR wavelengths. The H and K surface brightness images of GL 2136 reveal two bright limbs of nebulosity that extend radially from the star. This is interpreted as the preferential ejection of material along the walls of the outflow cavity. Evidence for the presence of a disc or toroid of material around each of the outflow sources is discussed. Polarization values from the reflection nebulosity around GL 2136 are observed to increase markedly between H and K. It is argued that this implies the presence of grains with a size distribution larger than that normally associated with the diffuse interstellar medium.