Constructing a Survey to Find Transits of Polluted White Dwarf Stars Using the New Van Vleck 24-inch Telescope

Transiting exoplanets orbiting white dwarf stars, though rare, are incredibly valuable to probe the long evolution of planets, potential secondary planet formation, and as targets for atmospheric characterization. We present work to use the new 24-inch automated telescope at the Van Vleck Observatory to search for such systems. Our sample is drawn from the extensive Gaia white dwarf list and modified to identify those stars that have heavy metals observed in their spectra. Such “polluted” systems are evidence of recent accretion that abundance analyses show is planetary in origin. Indeed, several such systems have recently been found to show evidence of transiting signatures of the tidally disrupted planetary material itself. We identify those that are visible from the Van Vleck Observatory and have not already been observed in depth by other survey telescopes. As of now, 93% of the white dwarf stars in the latest Gaia release have been observed for substantial periods of time by TESS or Kepler/K2. That leaves approximately 50 unobserved stars that also have polluted spectra. As part of the pilot study and the commissioning phase of the automated capabilities for the telescope, we focus on the star LB 1188 and can conclude with 100% confidence that LB 1188 does not have a transit with a period less than 5.3 hours and with 70% confidence does not have a transit with a period of <12 hours. We explore the future prospects of searching the remaining targets in our sample, and fully sampling periods in the 4-40 hour timeframe, which corresponds to the habitable zone for these low luminosity stars. We gratefully acknowledge the National Science Foundation’s support of the Keck Northeast Astronomy Consortium’s REU program through grant AST-1950797.