Spectral analysis of ultra-cool white dwarfs polluted by planetary debris

Abbigail K. Elms, Pier-Emmanuel Tremblay, Boris T. Gänsicke +5

We identify two ultra-cool ($T_{\mathrm{eff}}<4000$ K) metal-polluted (DZ) white dwarfs WDJ2147$-$4035 and WDJ1922$+$0233 as the coolest and second coolest DZ stars known to date w…