NGC 40: osservazione visuale, fotografia e caratteristiche fisiche

Details NGC 40: osservazione visuale, fotografia e caratteristiche fisiche NGC 40: osservazione visuale, fotografia e caratteristiche fisiche

Aug 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006asuai...4...38b&link_type=abstract

Astronomia. La rivista dell'Unione Astrofili Italiani (ISSN 0392-2308), N. 4, p. 38 - 41 (luglio-agosto 2006)

Astronomy and Astrophysics

Astronomy

Planetary Nebulae: Observations

Scientific paper

We have revisited the planetary nebula NGC 40 by means of visual observations and digital photos. The visual observation is difficult for the moderate brightness of the nebula. The interference filter OIII doesn't enhance the contrast, since the nebula belongs to a small group of PN showing a very-low level of ionization. The digital photo is a good tool of investigation to deepen the elements already found visually; we suggest a focal ideal of 1900/2200 mm and recommend the use of the Hα+NII filter. Probably, NGC 40 is the result of two consecutive mass-loss events characterized by a different speed of the stellar wind: in the first, long phase the dense and slow wind of the AGB star creates a neutral, almost spherical nebula which is denser in the equatorial regions; later on, an isotropic fast wind interacts with the slow wind and generates a bipolar structure ionized by the hot star, which is evolving towards the white dwarf region of the H-R diagram. The external zones of the nebula show the presence of the AGB halo - constituted by a series of concentric shells - and of some filaments - suggesting a possible interaction of NGC 40 with the old supernova remnant CTA 1.

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