Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981mnras.195..831c&link_type=abstract
Monthly Notices of the Royal Astronomical Society, vol. 195, June 1981, p. 831-837.
Astronomy and Astrophysics
Astronomy
19
Astronomical Models, Emission Spectra, Line Spectra, Quasars, Ubv Spectra, Luminosity, Lyman Alpha Radiation, Lyman Spectra, Red Shift, Spectral Line Width
Scientific paper
To obtain a model for the optical spectrum of an average quasar, a study is made of 277 quasars for which UBV spectra are available, and the mean optical spectrum is defined in terms of two parameters: (1) the power-law spectral index of the continuum and (2) the equivalent width of the Lyman alpha line. Natzer and Davidson (1979) have given average values of the observed intensities of 14 quasar emission lines relative to Lyman alpha, which are included in the spectrum synthesis. The mean optical spectrum of quasars is represented by a power-law continuum of the spectral index being equal to 0.5 + or - 0.1, with allowance being made for galactic extinction. The variation in the mean optical spectral index with quasar luminosity and redshift is also discussed, making it possible to determine whether or not there is a significant change in the mean slope of the continuum towards the ultraviolet; for this case, a steepening of the mean optical spectrum towards shorter wavelengths is noted.
Cheney J. E.
Rowan-Robinson Michael
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