High resolution imaging and spectroscopy of the Serpens reflection nebula (SRN). Evidence of a latitude-dependent wind

Abstract

An optical study (high resolution images and long-slit spectra in the Her range) of the Serpens reflection nebula (SRN) is presented. The SRN is a bipolar nebula illuminated by the low mass pre-main-sequence (PMS) star Serpens/SVS 2. The Ho profile of Serpens/SVS 2 is shown to be very broad (the width at a 10% of the peak intensity is 13.1 Angstrom (similar to 600 km/s)). The profile has three emission peaks centered at -137, 5 and 100 km/s. The relative strength of the peaks varies with the slit orientation. The blue and redshifted components have similar intensities at low inclinations (PA = -55 degrees and PA = -30 degrees) while at high inclinations the blueshifted component is weaker than the redshifted suggesting a significant contribution of absorption by low latitude outflowing gas. These profiles could be produced in a rotating, latitude dependent wind with the outflow axis parallel to the disk axis. The nebular H alpha profile is double peaked; it has a blue and a redshifted component at the same velocities as the star. The profile shows no significant variations along a given PA; the emission is best explained by single scattering of the stellar radiation. The absence of the 0-velocity emission component is suggestive of the presence of warm absorbing gas within a few stellar radii. There are several knots of gas and dust embedded within the north-western (NW) nebular lobe. These knots are connected by a faint emission, defining a helical path around the major axis of the nebula. This area is also characterized by an unusually large polarization that reaches a 30-40% at 0.95 mu m that is consistent with a concentration of large and reflecting dust grains that are presumably ice coated carbon grains. This region coincides with a ridge of hot (T similar or equal to 35 K) dust detected by IRAS along: the major axis of the SRN.