We investigate the integrated far-ultraviolet ( FUV ) emission from globular clusters .
We present new FUV photometry of M 87 ’ s clusters based on archival HST WFPC2 F170W observations .
We use these data to test the reliability of published photometry based on HST STIS FUV-MAMA observations , which are now known to suffer from significant red-leak .
We generally confirm these previous FUV detections , but suggest they may be somewhat fainter .
We compare the FUV emission from bright ( M _ { V } < -9.0 ) clusters in the Milky Way , M 31 , M 81 and M 87 to each other and to the predictions from stellar populations models .
Metal-rich globular clusters show a large spread in FUV - V , with some clusters in M 31 , M 81 and M 87 being much bluer than standard predictions .
This requires that some metal-rich clusters host a significant population of blue/extreme horizontal branch ( HB ) stars .
These hot HB stars are not traditionally expected in metal-rich environments , but are a natural consequence of multiple populations in clusters – since the enriched population is observed to be He-enhanced and will therefore produce bluer HB stars , even at high metallicity .
We conclude that the observed FUV emission from metal-rich clusters in M 31 , M 81 and M 87 provides evidence that He-enhanced second populations , similar to those observed directly in the Milky Way , may be a ubiquitous feature of globular clusters in the local universe .
Future HST FUV photometry is required to both confirm our interpretation of these archival data and provide constraints on He-enriched second populations of stars in extra-galactic globular clusters .