The Search for White Dwarf Binaries in Astronomical Survey Data

Abstract

Extremely low mass (ELM) white dwarfs are excellent laboratories for studying a variety of astrophysical phenomena, including common-envelope evolution, gravitational wave emission, and merger physics. A significant amount of work has been done to identify extremely low mass white dwarfs in the northern hemisphere using various photometric surveys, such as SDSS and Pan-STARRS.

In this dissertation, I present my follow-up observations of a low-mass, eclipsing, white dwarf binary and use the data to begin the process of directly measuring the binary's rate of orbital decay due to gravitational wave emission. These measurements can be used to obtain an independent measurement of the mass of the binary as well as constrain the effects of tides through a measured offset in orbital decay rate from a purely gravitational wave model (see Piro, 2011; Benacquista et al., 2011).

I then begin the search for ELM white dwarfs in the southern hemisphere (the ELM Survey South) through a large, targeted, spectroscopic survey using the SOAR 4.1-meter telescope. This search makes use of the southern-sky photometric surveys ATLAS and SkyMapper to identify a population of white dwarf binaries in color-color space which yields a small number of low-mass white dwarfs in a large pool of candidates. The target selection criteria are expanded to include the European Space Agency's Gaia Data Release 2 astrometry and photometry as soon as it became available. By using reliable parallax measurements and precise magnitudes, one is able to selectively target ELM white dwarfs with significantly higher accuracy than when using a pure photometric approach.

In preparation for the next phase of the ELM Survey South, I make use of the Zwicky Transient Facility (ZTF) public photometric survey to demonstrate the effectiveness of identifying exotic variables, including double white dwarf binaries, in large survey data sets. I make use of the Box Least Squares (BLS) period finding algorithm to identify eclipsing binaries within the public ZTF data archive and present photometric and spectroscopic analyses to a select few systems, including white dwarfs and hot subdwarf stars with main sequence companions. The methods developed here will be used as a starting point towards expanding the search for ELM white dwarfs in the southern hemisphere with the upcoming large-scale photometric surveys BlackGEM and the Vera Rubin Observatory's LSST program.