Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981mnras.196..857p&link_type=abstract
Monthly Notices of the Royal Astronomical Society, vol. 196, Sept. 1981, p. 857-887. Research supported by the Consiglio Nazion
Astronomy and Astrophysics
Astronomy
106
Astronomical Spectroscopy, Galactic Structure, Iue, Seyfert Galaxies, Ultraviolet Astronomy, Astronomical Photometry, Data Acquisition, Emission Spectra, Spectral Energy Distribution, Spectral Line Width, Ultraviolet Spectroscopy
Scientific paper
Low resolution ultraviolet spectroscopic monitoring of NGC 4151, the brightest Type 1 Seyfert galaxy, with the IUE from February, 1978 to January, 1979, is presented. Data acquisition and reduction are described. Observations were made at seven different epochs. Optimum exposure times, when the object is bright, were found to be 25-30 min and 50-60 min in large and small apertures respectively. When the object was faint or when a better signal-to-noise ratio in the continuum was required, a large-aperture exposure of 40-50 min was added. After the wavelength scale was determined for each spectrum, data obtained on the same day were averaged and regions affected by saturation, fiducials, geocoronal Lyman alpha emission and particle events were excluded from the mean spectra. Fifteen absorption features (most of which arise in the nucleus of NGC 4151) are identified and their equivalent widths measured. Velocity variations in the absorption region are indicated by changing V/R ratios in the overall C IV feature. The Si IV lines are unsaturated and must therefore be broad. The strong emission lines include those seen in quasars. The intensities of the high-ionization emission lines are variable, as are the linewidths of C IV.
Boksenberg Alec
Bromage Gordon E.
Clavel Jean
Elvius Aina
Gondhalekar P. M.
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