A white dwarf cooling age of 8 Gyr for NGC 6791 from physical separation processes

Understand

NGC 6791 is a well studied open cluster1 that it is so close to us that can be imaged down to very faint luminosities.

• The main sequence turn-off age (~8 Gyr) and the age derived from the termination of the white dwarf cooling sequence (~6 Gyr) are significantly different.
• One possible explanation is that as white dwarfs cool, one of the ashes of helium burning, 22Ne, sinks in the deep interior of these stars.
• At lower temperatures, white dwarfs are expected to crystallise and phase separation of the main constituents of the core of a typical white dwarf, 12C and 16O, is expected to occur.