Tracing outer planetary systems through white dwarf pollution in wide binaries

Abstract

White dwarf (WD) atmospheric metal pollution provides strong evidence for the presence of remnant planetary material and it can be used as an indirect tracer of outer planetary systems. We analyze whether the presence of a wide stellar companion affects the occurrence of outer planetary systems by comparing the incidence of calcium (Ca) pollution in hydrogen-atmosphere WDs in wide binaries and in apparently single stars. We construct two sample pairs: a large homogeneous SDSS low-resolution spectroscopic set and a smaller high-resolution sample. For each WD, we measure Ca abundances or upper limits and compute detectability-corrected cumulative pollution fractions that account for variations in effective temperature, signal-to-noise ratio, and spectral resolution. In the SDSS-based samples, we find pollution fractions <1%, defined as the fraction of WDs with detected Ca, for both single WDs and WDs in wide binaries. After correcting for detectability, the cumulative abundance distributions of the two populations are statistically consistent. The same conclusion is obtained for the higher-resolution samples, despite their different raw detection fractions. Our results indicate no statistically significant difference in the occurrence rate of remnant outer planetary systems between single stars and stars with wide (~200 au) companions, within the current uncertainties. These uncertainties are significant because the samples contain only a small number of polluted WDs. The corrected detectability cumulative fraction approach used here provides a framework for comparing samples with different detection sensitivities and can be extended to larger spectroscopic datasets. Such samples will be required to determine whether wide stellar companions affect the survival and delivery of planetary material and to search for more subtle trends, for example, as a function of companion separation.