Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1977
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977apj...212...37b&link_type=abstract
Astrophysical Journal, Part 1, vol. 212, Feb. 15, 1977, p. 37-51. Research supported by the Science Research Council and Israel
Astronomy and Astrophysics
Astrophysics
69
Astronomical Spectroscopy, Galactic Radiation, Line Spectra, Seyfert Galaxies, Digital Techniques, Image Enhancement, Ionization Coefficients
Scientific paper
The Seyfert galaxy NGC 3516 was observed during 1975 using a digital image detector. Accurate measurements of emission-line intensities and profiles are presented. The narrow lines are emitted in a region with electron density roughly equal to 1100 per cu cm. Photoionization calculations made show that excitation by a central nonthermal source can explain the observed intensity of the high-excitation forbidden lines. A cooler gas, shielded from the central ionizing source, is suggested to explain the strong forbidden O II and N II lines observed. Broad multicomponent hydrogen lines are seen in the spectrum. A decrease in the intensity of H-beta by 30% in 5 weeks has been observed and was associated with a large enhancement of Fe II broad lines near 5270 A and a change of the H-alpha/H-beta line ratio. Short time continuum variations can explain the change observed in emission-line intensities, provided the atmosphere is optically thick to Balmer line radiation.
Boksenberg Alec
Netzer Hagai
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