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In the present paper, we performed the optical, astrometric and spectroscopic studies for the open star cluster NGC 6475 using Gaia DR3 data. Using the radial density profile, we estimated the radius of the cluster to be equal to 1.44°. It is located at a distance of 279 ± 17 pc and has a service life of 224 ± 26 Myr. The mean proper motions in RA are 268.50 ± 0.80 mas yr−1 and in DEC, they are −34.83 ± 0.70 mas yr−1. Using spectroscopic radial velocity data of Gaia DR3, the median radial velocity is −14.47 ± 1.92 km s−1. We determined the physical parameters (Teff, log g and V sin i) for 11 possible members of the B-type stars in the open cluster NGC 6475, using the Barbier–Chalonge–Divan (BCD) spectrophotometry system. We also determined the projected rotational velocity of the stars by matching them with the theoretical LTE model and located our studied stars over the HR diagram. From the 11 studied B-type stars, we found six members from them. [ABSTRACT FROM AUTHOR]

• By using BCD Method we determine the fundamental parameters (T eff , log g, spectral type, and luminosity class) of eleven B stars in open clusters IC2391. • Using multi-color magnitude diagrams (Gaia DR3) we determined the age, color excess, and distance of IC2391. • We estimated the core and limiting radii of the open cluster IC2391. In this paper, we present the stellar parameters of individual B-type stars in the IC 2391 young open cluster, using the Barbier-Chalonge-Divan (BCD) Spectrophotometry System, to obtain stellar fundamental parameters from direct measurements of the Balmer discontinuity. This method is optimally suited for late B-stars to determine stellar fundamental parameters, such as effective temperatures, surface gravities, and spectral types, of the stars in the field of IC 2391. We also determined the projected rotational velocity of the stars by matching them with the theoretical LTE model and located our studied stars over the HR diagram. We used the optical, astrometric, and spectroscopic radial velocity data of Gaia DR3 to obtain fundamental parameters of the open cluster IC 2391. For the first time, we used the radial density profile to determine the radius of the cluster. We found that radius to be equal to 1.43 degrees. From 229 members, we found four B-member stars. [ABSTRACT FROM AUTHOR]