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Current issues in the study of planetary nebulae
One of the problems in the study of planetary nebulae - is the exact determination of the distance to them. For some nearby planetary nebulae may calculate the distance from us, using the measured parallax expansion: a high-resolution imagery from a few years ago, demonstrating the expansion of the nebula perpendicular to the ray of view, and spectroscopic analysis of the Doppler-shift will make it possible to calculate the rate of expansion along the beam. Comparison of the angular expansion velocity obtained from the expansion will make it possible to calculate the distance to the nebula.
The existence of such a diversity of nebulae is the subject of heated debates. Widely believed that the reason for this may be the interaction between the substance is removed from a star with different velocities. Some astronomers believe that the double star system is responsible, at least for the most complex shape of planetary nebulae. Recent studies have confirmed the presence of several planetary nebulae of powerful magnetic fields, the assumption that what has been put forward. Magnetic interaction with the ionized gas can also play a role in the development of some forms of them.
At the moment there are two different methods of detection of metals in the nebula based on the different types of spectral lines. Sometimes the two methods give quite unlike the results. Some astronomers are inclined to explain the existence of weak fluctuations of temperature in the planetary nebula. Others believe that the differences in observations are too stark to explain them by means of thermal effects. They make assumptions about the existence of cold clots containing a very small amount of hydrogen. However, clots, which in their opinion, can explain the difference in the assessment of the number of metals, has never been observed.