[Previous] | [Session 6] | [Next]
R.H. Rubin, N. Bhatt (NASA/Ames), R.J. Dufour, B. Buckalew (Rice), M.J. Barlow, X. Liu, P.J. Storey (UC London), B. Balick (U Washington), G.J. Ferland (U Kentucky), J.P. Harrington (U Maryland), P.G. Martin (U Toronto)
We present new HST/WFPC2 imagery for the planetary nebula (PN) NGC 7009. Observations were made in line filters F437N, F487N, F502N, and F656N plus continuum filter F547M. The primary goal was to develop a high spatial resolution (~0.1'') map of the intrinsic line ratio [\ion{O}{3}] 4363/5007 and thereby evaluate the electron temperature (Te) and the mean-square Te variation (t2) across the nebula. In this process we developed an extinction map from the F487N (H\beta) and F656N (H\alpha) images by comparing the observed line ratios in each pixel to the theoretical ratio and computing a c(H\beta) map which was used to correct the observed 4363/5007 ratios for reddening. As has been known, extinction is not large for this PN as we further demonstrate in our reddening map.
The most difficult and uncertain step is to extract the flux for [\ion{O}{3}] 4363 from the F437N data. Because this line is relatively weak, the continuum contribution to the observed F437N filter data is not negligible. Additionally, it is necessary to adjust for H\gamma ``leakage" in the F437N bandpass. Because the dominant contribution to the nebular continuum for NGC~7009 is recombination processes, we correct for the continuum emission as well as the H\gamma ``leakage" into the F437N bandpass using our F487N (H\beta) image. A preliminary tie-in with ground-based spectra indicates this is best done by subtracting 0.012*F487N from F437N. We present a picture of the [\ion{O}{3}] Te map, as well as our determinations of t2. The preliminary map is rather uniform; almost all values are between 9000~-- 10500~K, with the higher Tes closely coinciding with the inner He++-zone as seen in blue in the WFPC2 image of Balick et~al. (1998, AJ, 116, 360). Improvements are in progress that utilize our recent HST/STIS long-slit spectra to provide excellent co-spatial registration with the WFPC2 data to test/refine our methodology and analysis.
Supported by AURA/STScI grant related to GO-8114.
The author(s) of this abstract have provided an email address for comments about the abstract: rubin@cygnus.arc.nasa.gov