Binary Central Stars of Planetary Nebulae Discovered Through Photometric Variability. V. The Central Stars of Hatr 7 and Eso 330-9

Todd C. Hillwig, Valparaiso University
David J. Frew, University of Hong Kong
Nicole Reindl, University of Leicester
Hannah Rotter, Valparaiso University
Andrew Webb, Valparaiso University
Steve Margheim, Gemini South Observatory


We find the central stars (CSs) of the planetary nebulae (PNe) HaTr 7 and ESO 330-9 to be close-binary systems. Both have orbital periods of less than half a day and contain an irradiated cool companion to the hot CS. We provide light curves, spectra, radial velocity curves, orbital periods, and binary modeling results for both systems. The binary modeling leads to system parameters, or ranges of allowed parameters for each system. We find that for the CS of HaTr 7 we need to use limb-darkening values for the cool companion that are different than the expected values for an isolated star. We also fit the CS spectrum to determine log g and temperature values independent of the binary modeling. For ESO 330-9 we find that based on our binary modeling, the hot CS is most likely a postred giant branch (RGB) star with a mass of around 0.4 M. We discuss our derived stellar and nebular parameters in the broader context of close-binary CSs and their surrounding planetary nebulae (PNe). We also discuss the present status of known or suspected post-RGB stars in PNe.