First discovery of an ultra-cool white dwarf benchmark in common proper motion with an M dwarf

Understand

Ultra-cool white dwarfs are among the oldest stellar remnants in the Universe.

• Their efficient gravitational settling and low effective temperatures are responsible for the smooth spectra they exhibit.
• For that reason, it is not possible to derive their radial velocities or to find the chemistry of the progenitors.
• The best that can be done is to infer such properties from associated sources, which are coeval.