Star formation around three co-moving HAeBe stars in the Cepheus Flare
  The presence of three more Herbig Ae/Be (HAeBe) stars in the Cepheus Flare
within a 1.5$^{\circ}$ radius centered on HD 200775 suggests that star
formation is prevalent in a wider region of the LDN 1147/1158, LDN 1172/1174,
and LDN 1177 clouds. A number of young stellar objects (YSOs) are also found to
be located toward these clouds. Various star formation studies indicate ongoing
low-mass star formation inside this region. Sources associated with less
near-infrared (IR) excess and less H-alpha emission raise the possibility that
more low-mass YSOs, which were not identified in previous studies, are present
in this region. The aim is to conduct a search for additional young sources
that are kinematically associated with the known YSOs and to characterize their
properties. Based on the Gaia DR2 distances and proper motions, we found that
BD+68 1118, HD 200775, and PV Cep are spatially and kinematically associated
with known YSOs. Using the Gaia DR2 data, we identified 39 co-moving sources
around BD+68 1118. These sources are characterized using optical and near-IR
color-color and color-magnitude diagrams. We estimated a distance of 340+/-7 pc
to the whole association that contains BD+68 1118, HD 200775, and PV Cep. Based
on the distance and proper motions of all the known YSOs, a total of 74
additional co-moving sources are found, of which 39 form a loose association
surrounding BD+68 1118. These sources are predominantly M-type with ages of
$\sim$10 Myr and no or very little near-IR excess emission. The positive
expansion coefficients obtained via the projected internal motions of the
sources surrounding BD+68 1118 and HD 200775 show that these sources are
expanding with respect to their HAeBe stars. A spatio-temporal gradient of
these sources toward the center of the Cepheus Flare Shell supports the concept
of star formation triggered by external impacts.
