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NGC 6990



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A large sample of southern IRAS galaxies - Spectral classes and superclustering
Results are presented of an extensive spectroscopic survey of IRASgalaxies, in three Southern-Hemisphere fields totaling about 0.5 sr.Spectroscopic observations have been made of 527 galaxies which arecandidates for 474 IRAS sources. Together with published data, there arenow measured redshifts for almost 850 of the 1178 selected IRAS galaxiesin these fields. This measured sample includes nearly all galaxies athigh redshifts, and hense high infrared luminosities, within thesefields. Classification of more than 350 of these galaxies usingemission-line ratios and line widths shows that about 90 percent havestarburst characteristics. Two distinct groups of starburst galaxies inthe sample display forbidden O III-line intensities which significantlyexceed those observed in optically selected starburst galaxies. One ofthese groups, with strong N II forbidden lines, may be related to linersand/or Seyfert galaxies. The other, with weak N II forbidden-lineemission, displays unusually narrow lines; this group is interpreted interms of the youngest phase of starburst activity.

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Planetary nebulae - IUE results
The results of IUE observations of planetary nebulae are listed anddiscussed. With regard to the nebulae themselves, advances inunderstanding the density and temperature profiles across the nebula,the nebular continuum, the ionization structure, the chemicalcomposition, and the nebular dust are presented. With regard to thecentral stars, the mass loss phenomenon from fast winds, thedetermination of the temperature of the nuclei and the consequentimprovement of the star's HR diagram, and the chemical composition ofthe stellar surface layers are considered.

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Observation and Astrometry data

Right ascension:20h59m56.90s
Aparent dimensions:1.318′ × 0.525′

Catalogs and designations:
Proper Names   (Edit)
NGC 2000.0NGC 6990

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