What would you need to measure for a planetary nebula (see the image below)to determine how long ago its parent star died?

Question

Quizplus · Accepted Answer

To determine how long ago the parent star of a planetary nebula died, we need to measure the nebula's radius and expansion velocity. The expansion velocity can give us an estimate of how long ago the star exploded and formed the nebula, and the radius can help us estimate the age of the nebula. The mass and radius of the white dwarf are not directly related to the age of the nebula, and the nebula's temperature is also not a good indicator of its age.

What Would You Need to Measure for a Planetary Nebula