We present new Hubble Space Telescope (HST)/WFPC2 imagery and STIS long-slit spectroscopy of the planetary nebula NGC 7009. The primary goal was to obtain high spatial resolution of the intrinsic line ratio [O III] 4364/5008 and thereby evaluate the electron temperature (Te) and the fractional mean-square Te variation (tA2)across the nebula. The WFPC2 Temap is rather uniform; almost all values are between 9000–11 000 K, with the higher Te values closely coinciding with the inner He++ zone. The results indicate very small values–≲0.01– for tA2 throughout. Our STIS data allow an even more direct determination of Te and tA2, albeit for a much smaller area than with WFPC2. We present results from binning the data along the slit into tiles that are 0.5-arcsec square (matching the slit width). The average [O III] temperature using 45 tiles (excluding the central star and STIS fiducial bars) is 10 139 K; tA2 is 0.0035. The measurements of Tereported here are an average along each line of sight. Therefore, despite finding remarkably low tA2, we cannot completely rule out temperature fluctuations along the line of sight as the cause of the large abundance discrepancy between heavy element abundances inferred from collisionally excited emission lines compared to those derived from recombination lines.

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Published in Monthly Notices of the Royal Astronomical Society, v. 334, issue 4, p. 777-786.

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2002 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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