Spectral analysis of early F-type supergiants

High or moderately-high dispersion spectra covering the wavelength interval 3800A° to 5000A° were obtained for ten luminous early F-type stars and an F8Ia supergiant south of declination -15° . These spectroscopic plates have been used to measure line blocking, the profiles of the strongest lines (hydrogen and calcium K), and to determine the equivalent widths of as many metal lines as possible in this wavelength range. The line blocking measurements, hydrogen-line profiles and scanner or ubvy photometry data have been used with model atmosphere predictions to determine effective temperatures and gravities. A discrepancy between the gravity indicated by the Balmer jump and the Hy line profiles has been found in the most luminous stars. The gravities determined from the H profiles have been compared with the gravities derived from cluster members and there is found to be a small discrepancy, the gravities from the profiles being lower. Some evidence for the presence of macroscopic turbulent motions in the more luminous early F Ia stars and A Ia stars is presented, and it is shown that the inclusion of a turbulent pressure term in the equation of hydrostatic equilibrium largely removes the discrepancy between the gravity indicated by the Hy profiles and that indicated by the cluster members. A study of the rotational velocities of the program stars show that the early F Jab and lb stars exhibit very little or no macroturbulence. The observed rotational velocity of 0 Sco (a lb supergiant) shows that this star must have lost very little of its angular momentum during its evolution off the main sequence and must have rotated as a rigid body for some, if not all, of this phase of its evolution.