A census of young stellar population associated with the Herbig Be star
  HD 200775
  The region surrounding the well-known reflection nebula, NGC 7023,
illuminated by a Herbig Be star, HD 200775, located in the dark cloud L1174 is
studied in this work. Based on the distances and proper motion values from Gaia
DR2 of 20 previously known young stellar object candidates, we obtained a
distance of 335$\pm$11 pc to the cloud complex L1172/1174. Using polarization
measurements of the stars projected on the cloud complex, we show additional
evidence for the cloud to be at $\sim$ 335 pc distance. Using this distance and
proper motion values of the YSO candidates, we searched for additional comoving
sources in the vicinity of HD 200775 and found 20 new sources which show low
infrared excess emission and are of age $\sim$ 1 Myr. Among these, 10 YSO
candidates and 4 newly identified comoving sources are found to show X-ray
emission. Three of the four new sources for which we have obtained optical
spectra show H$\alpha$ in emission. About 80% of the total sources are found
within $\sim$ 1 pc distance from HD 200775. Spatial correlation of some of the
YSO candidates with the Herschel dust column density peaks suggests that star
formation is still active in the region and may have been triggered by HD
200775.
