Clustering of low mass stars around Herbig Be star IL Cep -- Evidence of
  "Rocket Effect" using Gaia EDR3 ?
  We study the formation and the kinematic evolution of the early type Herbig
Be star IL Cep and its environment. The young star is a member of the Cep OB3
association, at a distance of 798$\pm$9 pc, and has a "cavity" associated with
it. We found that the B0V star HD 216658, which is astrometrically associated
with IL Cep, is at the center of the cavity. From the evaluation of various
pressure components created by HD 216658, it is established that the star is
capable of creating the cavity. We identified 79 co-moving stars of IL Cep at 2
pc radius from the analysis of {\textit Gaia} EDR3 astrometry. The transverse
velocity analysis of the co-moving stars shows that they belong to two
different populations associated with IL Cep and HD 216658, respectively.
Further analysis confirms that all the stars in the IL Cep population are
mostly coeval ($\sim$ 0.1 Myr). Infrared photometry revealed that there are 26
Class II objects among the co-moving stars. The stars without circumstellar
disk (Class III) are 65\% of all the co-moving stars. There are 9 intense
H$\alpha$ emission candidates identified among the co-moving stars using IPHAS
H$\alpha$ narrow-band photometry. The dendrogram analysis on the Hydrogen
column density map identified 11 molecular clump structures on the expanding
cavity around IL Cep, making it an active star-forming region. The formation of
the IL Cep stellar group due to the "rocket effect" by HD 216658 is discussed.
