Bipolar outflow sources in the Serpens core: SVS 2 and SVS 20

Polarimetric maps of the Serpens Reflection Nebula (SRN) obtained at H (1.65 μm) and K (2.20 μm) show centrosymmetric patterns of polarization vectors centred about each of the protostars SVS 2 and SVS 20. These patterns indicate that evacuated, bipolar cavities surround each source. Such bipolar structures suggest the presence of outflows. While the polarization discs are not apparent in these maps, the position angles of the discs can be inferred from the elliptically symmetric morphology of the polarization pattern. We determine these position angles to be 40°± 10° for SVS 2 and 140°± 10° for SVS 20. Three ‘knots’ of emission are evident in a narrow-band image of the SRN taken at the v = 1 → 0 S(l) transition of molecular hydrogen. The association of these knots with the projected directions of the polar axes of the SVS 2 and SVS 20 outflow cavities suggest the knots are collisionally excited by outflows from these two protostars. We obtained high spatial resolution images of the SVS 20 binary system through four narrow-band filters at and near the 3.1-μm H2O ice absorption feature. The northern (SVS 20N) and southern (SVS 20S) components of the 1.6-arcsec separation binary are well separated in these images. We measured the intensity of SVS 20S relative to that of SVS 20N using a small 1.1 × 1.1 arcsec2 synthetic aperture and a larger 1.1 × 8.1 arcsec2 synthetic aperture oriented east-west. We found that the relative intensity was smaller through the larger aperture for all of the narrow-band filters except the 3.1-μm filter. These data imply that ice must exist within the local circumstellar environment of this binary. Images of the SRN reveal that the cometary nebula EC 81 has faded by at least two magnitudes at H and K between 1989 and 1994. The rapid and dramatic drop in the near-infrared brightness of EC 81 suggests that this protostar may be in a post-FUor or post-EXor outburst phase. Based on recently presented evidence for several other flaring or fading episodes over the last two decades for other protostars in or near the SRN, we conclude that such FUor or EXor activity may be fairly common in the Serpens star-forming regions.