Optical emission line profiles of symbiotic stars

Summary

Introduction

High resolution (≤ 10 km s⁻¹) spectra of a selection of symbiotic stars have been obtained using the Manchester Echelle Spectrograph and IPCS on the 2.5 m Isaac Newton Telescope on La Palma, as a preliminary to a high resolution survey of all known symbiotic stars now being conducted from the INT and ESO. In several cases, the [OIII] 5007 Å region shows complex structure, probably originating in extended outflows. However, the Hα line in many objects shows a well-known double-peaked profile (see e.g. Anderson et al. 1980). This is very reminiscent of those associated with dwarf novae, where observations through eclipse indicate that the emission originates in the accretion disc surrounding the white dwarf component of the semi-detached binary (see e.g. King, this volume).

If this were also the case with symbiotic systems, then theoretical modelling of the line profiles would enable us to constrain the all-important binary parameters. Our preliminary aim, however, is to determine whether such line profiles can be reconciled with emission from accretion discs at all. Anderson et al. (1980) concluded that the case still remained ambiguous.

The model

In order to construct theoretical line profiles from accretion discs, we have adapted the optically thick disc model of Home & Marsh (1986) producing double-peaked profiles which have a deep “V”-shaped central reversal. These match the observed profiles more closely than earlier (optically thin) models (e.g. Smak 1969).