1997A&A...327..191M

We have analyzed the optical spectra of 67 symbiotic stars and objects suspected of being symbiotic, and found 18 new symbiotic systems. This is the largest homogeneous set of optical spectrophotometric data for symbiotic binaries ever studied. We have derived the reddenings and distances for all systems, estimated the IR classes (S and D) for the new systems, and determined the location of the hot components in the Hertzsprung-Russell diagram. Our study confirms the result of previous works, based on much smaller samples, that the hot components lie on the post-AGB tracks. We argue that most of them are white dwarfs for which accretion has reactivated the hydrogen shell burning, rather than hot white dwarfs that have recently ejected planetary nebulae. The hot component luminosities are found to be correlated with the nature of the cool giant, and the luminosity in the λ6825Å emission line. Our finding supports Schmid's interpretation of the 6825 emission in terms of Raman scattering of O VI 1032 by neutral hydrogen.