Planetary nebula with a neutral envelope?
IUE ultraviolet spectral recording for a low excitating planetary nebula NGC 6369 is obtained. The very strong doublet 2800 Mgii in emission as well as not less strong absorption line 2852 Mgi are discovered in the spectrum of this nebula. It is shown that the resonance line 2852 Mgi may originate only in a neutral envelope, around the nebula, consisting of neutral hydrogen, neutral magnesium, and dust particles (Hi+Mgi). The importance of this absorption line as a powerful indicator of the discovery of neutral envelopes around the planetary nebulae is outlined.
The possibility of the existence of one more envelope—transition zone—immediately contacting with the bright that is ionized part of nebula (Hii+Mgii) is also shown. The transition zone consists of neutral hydrogen, ionized magnesium, and dust particles (Hi+Mgii), main parameters of this zone are also obtained (Table IV).
The temperature of the central star of this nebula is obtained for the first time:T*=48000 K. Continuous background in the interval 2600–3000 Å is identified with Balmer continuum with electron temperatureT e =12500 K.
KeywordsMagnesium Transition Zone Dust Particle Absorption Line Resonance Line
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