Star formation around three co-moving HAeBe stars in the Cepheus Flare

Context. 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 Hα 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 coefficients 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.