The nature of the hot subdwarf SB 744.

Abstract

Various spectra in the visual wavelength range, one low-resolution ultraviolet spectrum, and color measurements in the red region have been taken to clarify the nature of the hot subdwarf SB 744. The colors and weak metallic lines as well as a G-band (CH) in the visual spectra indicate the existence of a cool companion, whereas the hydrogen and helium line spectrum is typical for a hot subdwarf. The model atmosphere analysis of the hydrogen and helium line spectrum yields that the primary is a typical OB-type subdwarf. There is some evidence for a similar strange abundance pattern as in other OB-type subdwarfs. From the measured colors, the strengths of the Mg I - lines, the G-band, and the weak resonance line of Ca I at 4227 A, it becomes evident that the companion is a K0-star, which contributes about 20 percent to the visual magnitude.