CCD Imagery of Planetary Nuclei: The Properties of the Central Stars of NGC 2440 and NGC 7027

Details CCD Imagery of Planetary Nuclei: The Properties of the Central Stars of NGC 2440 and NGC 7027 CCD Imagery of Planetary Nuclei: The Properties of the Central Stars of NGC 2440 and NGC 7027

Apr 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990apj...353..200h&link_type=abstract

Astrophysical Journal v.353, p.200

Astronomy and Astrophysics

Astronomy

27

Nebulae: Individual Ngc Number: Ngc 7027, Nebulae: Individual Ngc Number: Ngc 2440, Nebulae: Planetary, Spectrophotometry, Stars: Early-Type

Scientific paper

We report on the first results of a program of narrow-band imagery of planetary nebulae suspected of harboring exceedingly hot (T > 300,000 K), "massive" (M ≥ 1.0 Msun) central stars. Two of the most likely candidates are the nuclei of NGC 2440 and NGC 7027, for which Zanstra temperatures ˜350,000 K have been reported, based on narrow-band continuum imaging data. However, even with carefully chosen passbands, the continuum nebular emission for such objects swamps the flux from the central star. We have therefore combined narrow-band CCD imaging (in Hβ, in He II 4686 Å, and in the line-free continuum) with image-subtraction techniques in order to isolate the central stars from the background nebulae, and to derive their magnitudes and Zanstra temperatures. We measure V = 17.6 ± 0.15 for the nucleus of NGC 2440 and V = 16.18 ± 0.2 for the nucleus of NGC 7027, leading to a value of Teff ≍ 200,000 K for the central stars of both nebulae. Using published evolutionary tracks for planetary nuclei, we estimate central star masses of 0.62#).70 Msun for NGC 2440 and 0.65-0.70 for NGC 7027. These values are not much higher than the norm for planetary nuclei, which is estimated at 0.60 Msun.

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