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

Abstract

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.