Spectroscopy of B and Be Stars in the Very Young Open Star Cluster IC 1805

Based on moderate-resolution spectra in the range 4200–5200 Å, we have studied late O–early B stars in the very young open star cluster IC 1805. The temperatures of the stars under study have been derived by the differential method in which simple parameters were chosen for a number of spectral lines and were then compared with the analogous parameters from an extensive sample of O–B stars. Accurate \(T_{\textrm{eff}}\) estimates have been obtained for them from model atmospheres. Applying this method for the sample of objects under study has allowed the cluster age \(t=2\pm 0.5\) Myr and distance modulus \((v-V)_{0}=11.5^{m}\) to be determined with confidence. We have studied the spectroscopic variability of the emission spectrum for the sole Be star of early spectral type B MWC 50 that is a member of the cluster. We show that it is a classical Be star probably seen pole-on and has no long-term variability of the profiles typical for many classical Be stars.