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Emission-line variability and the broad-line region of quasi-stellar objects. I - Time scales and photon densities
Zheng, Wei; Burbidge, E. Margaret; Smith, Harding E.; Cohen, Ross D.; Bradley, Steven E.
AA(California, University, La Jolla), AB(California, University, La Jolla), AC(California, University, La Jolla), AD(California, University, La Jolla), AE(California, University, La Jolla)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 322, Nov. 1, 1987, p. 164-173. (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Emission Spectra, Line Shape, Periodic Variations, Photons, Quasars, Spectral Line Width, Astronomical Models, Density Distribution, Photoionization, Red Shift, Temporal Distribution, Wavelengths
Bibliographic Code:


Spectroscopic data for five low-redshift QSOs taken over several years are presented as evidence for emission-line variability in QSOs. The broad hydrogen emission lines in the QSOs 0026 + 129, 1202 + 281, 1612 + 261, and 2141 + 175 are found to vary in step with their underlying continua. Another QSO, 2135 - 147, shows an increase in the intensities of its hydrogen lines five years after the increase in its continuum level. The inferred upper limit to the size of the broad emission line region is smaller than 3 lt-yr, probably as small as 0.4 lt-yr for 0026 + 129, if the line-emitting region is spherically distributed. Such a small size implies a very high density of ionizing photons, of the order of 10 to the 10th/cu cm. A very high nucleon density must then be assumed in order to obtain a value of the ionization parameter consistent with current photoionization models.

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