The visual magnitude of the central star of NGC 6537 is 22.4 or fainter. The Zanstra temperature of the central star derived from this magnitude is 500 000 K or higher. The Energy Balance method gives a temperature consistent with this value. The temperature given by the degree of nebular ionization is lower, but there is reason to believe that it is not reliable.
From the above magnitude and temperature, the radius of the central star is found. Using the core mass-radius relation it is shown that the core mass must be high, probably about 1 . The high temperature and high core mass are consistent with high mass evolutionary models except for the time of evolution, which must be at least an order of magnitude longer than predicted.
© European Southern Observatory (ESO) 2000
Online publication: October 24, 2000