Abstract:
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 ± 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 centre 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 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 (∼0.1 Myr). Infrared photometry revealed
that there are 26 Class II objects among the co-moving stars. The stars without circumstellar disc (Class III) are 65 per cent
of all the co-moving stars. There are nine intense H α emission candidates identified among the co-moving stars using IPHAS
H α 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.
