Galactic Globular and Open Cluster Fiducial Sequences in the Pan-STARRS1
  Photometric System
  We present the fiducial sequences of a sample of Galactic star clusters in
the five bands of the Pan-STARRS1 (PS1) photometric system (g_P1, r_P1, i_P1,
z_P1, y_P1). These empirical sequences -- which include the red giant and
sub-giant branches, the main sequence, and the horizontal branch -- were
defined from deep colour-magnitude diagrams reaching below the oldest
main-sequence turn-offs of 13 globular and 3 old open clusters covering a wide
range of metallicities (-2.4 < [Fe/H] < +0.4). We find excellent agreement for
the nine clusters in common with previous studies in similar photometric
systems when transformed to the PS1 system. Because the photometric and
spectroscopic properties of these stellar populations are accurately known, the
fiducials provide a solid basis for the interpretation of observations in the
PS1 system, as well as valuable constraints to improve the empirical
colour--$T_{eff}$ relations.
