Filamentary structure in planetary nebulae.
Abstract
Small-scale inhomogeneities in planetary nebulae were studied via photographic spectrophotometry in order to determine the characteristics of these features with respect to the ambient nebular gas. Untrailed spectrograms of eight planetaries yielded two types of data. First, relative intensity distributions along the projections of the spectrographic slit on the nebulae were produced to show the spatial variations in the emission from different atoms and ions. Then, relative emission4ine fluxes were derived and used to find the electron temperatures and densities of filamentary regions and their surroundings. Compared with the ambient gas, the filamentary regions show strongly intensified emission for nebular transitions of neutral and singly ionized atoms, while auroral lines of these species along with lines of hydrogen and neutral helium have less striking enhancements. The strengths of lines from more highly ionized species exhibit little or no correlation with filamentary features. In addition, the filamentary zones are consistently cooler and denser than their surroundings. The above characteristics are in agreement with recent theoretical predictions for such structure. Previously encountered ambiguities in electron temperature and density measurements and in chemical abundance determinations seem explainable in terms of filamentary structure. Hence, caution must be used in dealing with photoelectric data which represents emission integrated over large nebular volumes. Subject heading: planetary nebulae
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 1974
- DOI:
- 10.1086/152627
- Bibcode:
- 1974ApJ...187..283B