RUI: Understanding Close White Dwarf Binaries Using Planetary Nebula Central Stars

Between one third to one half of all stars are found in binary systems, and many in their late evolutionary stages will become close white dwarf (WD) binary stars, a short-lived stage consisting of either two closely spaced WDs or a WD-main sequence pair. These objects play an important role in many astrophysical contexts, including the “common envelope” (CE) phase in binary star evolution, non-spherical planetary nebulae (PNe) formation, cataclysmic variables (e.g., novae), as well as alternate pathways to type Ia supernovae (SNe), the latter serving as a key cosmological distance indicator.

Insights into the formation and evolution of these systems depends on expanding the list of known examples, particularly those making up the central stars in planetary nebulae (CSPNe), which is the primary goal of a research program at Valparaiso University. This work will also support direct participation by undergraduate research students and further develop astronomy labs utilizing the Southeastern Association for Research in Astronomy (SARA) Observatory.

Photometric and spectroscopic observing campaigns will be undertaken with the specific goal of doubling (from 90 to >160) the existing set of known close binary CSPNe. More detailed follow-up observations of the newly discovered binary CSPNe (as well as known examples) will be used with binary modeling to provide detailed system parameters such as each star’s mass, radius, and temperature.

The newly increased set of known parameters will then be used to better understand the formation of double white dwarf (DWD) binaries and white dwarf binaries with a main sequence (MS) companion. The research team is working on Monte Carlo analysis and binary evolution calculations for DWD systems. That work will be expanded and updated as the observed sample size increases.

The researchers will also use the results to test existing Monte Carlo, population evolution, and CE computations and the results will be available for other researchers to use as future constraints to their modeling. The results will also provide independent measures of DWD merger rates, SN Ia rates, and the SN Ia delay time distribution (DTD).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.