The O I] 1641A line as a probe of symbiotic star winds

TL;DR

This study investigates the O I] 1641A line as a diagnostic tool for neutral winds in symbiotic stars, revealing its potential to probe wind properties and activity through archival spectral data analysis.

Contribution

It systematically analyzes the O I] 1641A line in symbiotic stars using archival spectra, demonstrating its correlation with stellar activity and its diagnostic potential.

Findings

O I] 1641A line detected in many symbiotic stars

Line variations correlate with optical light curves and outbursts

Potential application in studying ionization-bounded regions in various sources

Abstract

The neutral oxygen resonance 1302A line can, if the optical depth is sufficiently high, de-excite by an intercombination transition at 1641A to a metastable state. This has been noted in a number of previous studies but never systematically investigated as a diagnostic of the neutral red giant wind in symbiotic stars and symbiotic-like recurrent novae. We used archival $IUE$ high resolution, and GHRS and STIS medium and high resolution, spectra to study a sample of symbiotic stars. The integrated fluxes were measured, where possible, for the O I 1302A and O I] 1641A lines. The intercombination 1641A line is detected in a substantial number of symbiotic stars with optical depths that give column densities comparable with direct eclipse measures (EG And) and the evolution of the recurrent nova RS Oph 1985 in outburst. In four systems (EG And, Z And, V1016 Cyg, and RR Tel), we find that the O I] variations are strongly correlated with the optical light curve and outburst activity. This transition can also be important for the study of a wide variety of sources in which an ionization-bounded H II region is imbedded in an extensive neutral medium, including active galactic nuclei, and not only for evaluations of extinction.