The Central Star of Planetary Nebula PHR 1315-6555 and its host Galactic
  Open Cluster AL 1
  PHR 1315-6555 is a rare case of a Galactic Planetary Nebula that is a proven
member of the Open Cluster AL 1. This allows its distance to be defined with
precision and thus the accurate measurement of its physical characteristics
along with the parameters of its Central Star (CS). In this work we use HST to
detect this unique CS and constrain the cluster's physical parameters. Our
results suggest that the cluster rests at a distance of $\sim$12 kpc, is highly
reddened, and has an age of around 0.66 Gyrs and a turn-off mass of $\sim$2.2
M$_\odot$. Our deep Colour Magnitude Diagram (CMD) suggests that the
metallicity of the cluster is subsolar (Z=0.006). Our photometric measurements
indicate that the PN's core is a faint blue star close to the nebular apparent
centre, with an observed dereddened visual VEGA magnitude of 21.82 $\pm$ 0.60.
A significant contribution from any possible binary companion is unlikely but
possible. Our results show that the CS has an effective Zanstra temperature of
around 113 kK and a mass of 0.58 M$_\odot$ providing a unique additional point
to the fundamental White Dwarf Initial-to-Final-Mass Relation.
