Dense circumstellar nebulae in wide binary central stars

Abstract

Detection of close binary central stars with periods of less than a day is now well-tested and routinely possible via photometric monitoring. For wide binary central stars with periods of weeks to years detection techniques are still in their infancy. Radial velocity monitoring programs are yet to be applied to very large samples and the method suffers from large systematic errors as well as intrinsic wind variability. One alternative we are exploring is the detection of dense circumstellar nebulae residing around a wide companion. The archetype of this class is EGB6 as revealed by HST imaging (Bond 2009). Here we present spectroscopic evidence for other EGB6-like central stars and discuss their relationship to symbiotic stars. A probable 12.5-day irradiated binary is also presented to demonstrate the limits of the photometric monitoring technique.