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Astron. Astrophys. 362, L17-L20 (2000)

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Letter to the Editor

The central star of the Planetary Nebula NGC 6537

S.R. Pottasch

Kapteyn Astronomical Institute, P.O. Box 800, NL 9700 AV Groningen, The Netherlands

Received 7 August 2000 / Accepted 19 September 2000


The fact that Space Telescope WFPC2 images of the planetary nebula NGC 6537 fail to show the central star is used to derive a limit to its magnitude: it is fainter than a magnitude of 22.4 in the visible. This is used to derive a lower limit to the temperature of the star. The Zanstra temperature is at least 500 000 K. The Energy Balance temperature is found to be consistent with this value, as is the ionization state of the nebula. Assuming a reasonable range of distances for the nebula, the radius of the star can be found. It is consistent with the mass-radius relation of a white dwarf of 0.9 [FORMULA] or higher.

Key words: stars: fundamental parameters – ISM: planetary nebulae: general – ISM: planetary nebulae: individual: NGC 6537

Send offprint requests to: S.R.Pottasch

Correspondence to: Kapteyn Institute, P.O. Box 800, Groningen, The Netherlands (pottasch@astro.rug.nl)

© European Southern Observatory (ESO) 2000

Online publication: October 24, 2000