In order to determine the precise effective temperature and surface gravity of warm stars, all synthetic spectral lines in the wavelength range of 4000-5700Å with T=6000-7750 K, and log g=3.5, 4.0, and 4.5 for [M/H]=0.0, Vrot=10 km s-1, and Vtubl=2 km s-1 were calculated using the SYNSPEC package(Hubeny, et al., 1995) and the Kurucz(1995) model. Then, the depth-ratios for all line pairs were investigated and we selected two and six depth-ratios appropriate for the surface gravity and temperature indicators, respectively. We plotted six grids with X- and Y-axes for the depth-ratios of surface gravity and temperature, respectively, for the simultaneous estimation of these two atmospheric parameters. This method was applied to the spectum of δ Scu for the determination of its temperature and surface gravity simultaneously.

Stromgren -system colors for 23 OV stars compiled by Crawford have been compared with colors calculated by Mihalas from non-LTE model atmospheres. In this way, effective temperatures of these stars have been determined and plotted against spectral type, c1 (u-b), (b-y), (U-B), and (B-V). Within the accuracy of the observations, effective temperatures derived from the photometry for these 23 main-sequence stars are found to be in good agreement with Contiis spectroscopical temperatures.

Photoelectric observations were made of four N stars (HD 51208, HD 75021, V 1942 Sgr, and RU Vir) at careful1y chosen discrete wavelengths between 7000 |AA a n d 11000 |AA with 30 |AA bandpass width. Their effective temperatures have been derived by fitting the black-body radiation curve to the observed continuum intensities at 7800 |AA , 9000 |AA a n d 10800 |AA . The resulting temperature ranges from 2500˚ K t o 2900 ˚ K . . It is probable that almost all the N stars belong to this range of temperature. However, the temperatures of very red N stars can not be well determined due to large variability and redistribution of their radiation energy arising from the graphite shells around them.

Optical thickness of Rosette Nebula for Lyman Continuum is examined with W. Gebel's data. And the effective temperatures of the six exciting 0 stars of the nebula are obtained on the assumption that O stars emit black body radiation. The results are found to be generally in between Spitzers old and revised values.