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The presence of three more Herbig Ae/Be (HAeBe) candidates in the Cepheus Flare within a 1.5° 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 found to be distributed toward these cloud complexes along with the HAeBe stars.
Various star formation studies clearly indicate ongoing low-mass star formation inside the clouds of this region. Sources associated
with less near-infrared excess and less H emission raise the possibility that more low-mass YSOs, which were not identified in
previous studies, are present in this region.
Aims. The aim is to conduct a search for additional young sources that are kinematically associated with the previously known YSOs
and to characterize their properties.
Methods. Based on the Gaia DR2 distances and proper motions, we found that the HAeBe candidates BD+68 1118, HD 200775,
and PV Cep are all spatially and kinematically associated with previously known YSOs. Based on the Gaia DR2 data, we identified a
number of co-moving sources around BD+68 1118. These sources are characterized using optical and near-infrared color-color and
color-magnitude diagrams.
Results.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 in this region, of which
39 form a loose association surrounding BD+68 1118. These sources are predominantly M-type sources with ages of 10 Myr and
no or very little near-infrared excess emission. The distribution of co-moving sources around BD+68 1118 is much more scattered
than that of sources found around HD 200775. The positive expansion coe cients obtained via the projected internal motions of the
sources surrounding BD+68 1118 and HD 200775 show that the co-moving sources are in a state of expansion 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. |
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