Astron. Astrophys. 323, 541-548 (1997)

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

Ana I. Gómez de Castro

Instituto de Astronomía y Geodesia (CSIC-UCM), Facultad de CC. Matemáticas, Universidad Complutense de Madrid (UCM), E-28040 Madrid, Spain

Received 10 April 1996 / Accepted 4 December 1996

Abstract

An optical study (high resolution images and long-slit spectra in the H   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 H   profile of Serpens/SVS 2 is shown to be very broad (the width at a 10% of the peak intensity is 13.1 Å ( 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 ( and ) 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   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 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 35 K) dust detected by IRAS along the major axis of the SRN.

Key words: ISM: reflection nebulae ISM: individual objects: Serpens Reflection Nebula ISM: jets and outflows stars: pre-main-sequence stars: mass-loss

* Based on observations carried out at the Calar Alto and Roque de los Muchachos Observatories.

Send offprint requests to: Ana I. Gómez de Castro

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Contents

• 1. Introduction
• 2. Observations
• 3. Results
  • 3.1. The Serpens/SVS 2 spectrum
  • 3.2. The reflection nebula
    • 3.2.1. The nebular H   line
    • 3.2.2. Physical properties of the nebular dust
  • 3.3. Detection of a Herbig-Haro nebulosity
• 4. Discussion
  • 4.1. Variability
  • 4.2. A latitude-dependent wind from Serpens/SVS 2
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

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