We analyze ultraviolet ( \sim 1500 Å ) images of the old open clusters M67 , NGC 188 , and NGC 6791 obtained with Ultraviolet Imaging Telescope ( UIT ) during the second flight of the Astro observatory in March 1995 .
Twenty stars are detected on the UIT image of M67 , including 11 blue stragglers , seven white dwarf candidates , and the yellow giant – white dwarf binary S1040 .
The ultraviolet photometry of the blue stragglers F90 ( S975 ) and F131 ( S1082 ) suggests that these stars have hot subluminous companions .
We present a semi-empirical integrated ultraviolet spectrum of M67 , and show that the blue stragglers dominate the integrated spectrum at wavelengths shorter than 2600 Å .
The number of white dwarfs in M67 is roughly consistent with the number expected from white dwarf cooling models .
Eight candidate sdB/sdO stars are detected in NGC 6791 , and two are detected in NGC 188 .
The luminosity range 1.10 < \log L/L _ { \sun } < 1.27 , derived from the ultraviolet photometry of the six sdB candidates , is consistent with theoretical models of metal-rich hot horizontal branch ( HB ) stars .
The fraction of hot HB stars in both NGC 6791 and NGC 188 is about 30 % , implying that the integrated spectra of both clusters should show a UV turnup at least as strong as that observed in any elliptical galaxy .