Zwicky Transient Facility and Globular Clusters: the Period-Luminosity
  and Period-Luminosity-Color Relations for Late-Type Contact Binaries
  In this work, we aimed to derive the $gri$-band period-luminosity (PL) and
period-luminosity-color (PLC) relations for late-type contact binaries, for the
first time, located in the globular clusters, using the homogeneous light
curves collected by the Zwicky Transient Factory (ZTF). We started with 79
contact binaries in 15 globular clusters, and retained 30 contact binaries in
10 globular clusters that have adequate number of data points in the ZTF light
curves and unaffected by blending. Magnitudes at mean and maximum light of
these contact binaries were determined using a fourth-order Fourier expansion,
while extinction corrections were done using the {\tt Bayerstar2019} 3D
reddening map together with adopting the homogeneous distances to their host
globular clusters. After removing early-type and "anomaly" contact binaries,
our derived $gri$-band PL and period-Wesenheit (PW) relations exhibit a much
larger dispersion with large errors on the fitted coefficients. Nevertheless,
the $gr$-band PL and PW relations based on this small sample of contact
binaries in globular clusters were consistent with those based on a larger
sample of nearby contact binaries. Good agreements of the PL and PW relations
suggested both samples of contact binaries in the local Solar neighborhood and
in the distant globular clusters can be combined and used to derive and
calibrate the PL, PW and PLC relations. The final derived $gr$-band PL, PW and
PLC relations were much improved than those based on the limited sample of
contact binaries in the globular clusters.
