The globular cluster ( GC ) system of our Galaxy contains four planetary nebulae ( PNe ) : K 648 ( or Ps 1 ) in M15 , IRAS 18333-2357 in M22 , JaFu 1 in Pal 6 , and JaFu 2 in NGC 6441 .
Because single-star evolution at the low stellar mass of present-epoch GCs was considered incapable of producing visible PNe , their origin presented a puzzle .
We imaged the PN JaFu 1 with the Hubble Space Telescope ( HST ) to obtain photometry of its central star ( CS ) and high resolution morphological information .
We imaged IRAS 18333-2357 with better depth and resolution , and we analyzed its archival HST spectra to constrain its CS temperature and luminosity .
All PNe in Galactic GCs now have quality HST data , allowing us to improve CS mass estimates .
We find reasonably consistent masses between 0.53 and 0.58 M _ { \odot } for all four objects , though estimates vary when adopting different stellar evolutionary calculations .
The CS mass of IRAS 18333-2357 , though , depends strongly on its temperature , which remains elusive due to reddening uncertainties .
For all four objects , we consider their CS and nebula masses , their morphologies , and other incongruities to assess the likelihood that these objects formed from binary stars .
Although generally limited by uncertainties ( \sim 0.02 M _ { \odot } ) in post-AGB tracks and core mass vs luminosity relations , the high mass CS in K 648 indicates a binary origin .
The CS of JaFu 1 exhibits compact bright [ O III ] and H \alpha emission , like EGB 6 , suggesting a binary companion or disk .
Evidence is weaker for a binary origin of JaFu 2 .