PHL 5038AB: is the brown dwarf causing pollution of its white dwarf host star?

Abstract

We present new results on PHL 5038AB, a widely separated binary system composed of a white dwarf and a brown dwarf, refining the white and brown dwarf parameters and determining the binary separation to be au. New spectra of the white dwarf show calcium absorption lines suggesting that the hydrogen-rich atmosphere is weakly polluted, inferring the presence of planetesimals in the system, which we determine are in an S-type orbit around the white dwarf in orbits closer than 17–32 au. We do not detect any infrared excess that would indicate the presence of a disc, suggesting that all dust present either has been totally accreted or is optically thin. In this system, we suggest that the metal pollution in the white dwarf atmosphere can be directly attributed to the presence of the brown dwarf companion disrupting the orbits of planetesimals within the system.