An astronomical researcher whose work with Beverley J. Wills tested whether a double quasar represented two sources or two lensed images. The similar absorption-line redshifts and line widths supplied evidence for a shared distant source. The analysis also examined differences in brightness and reddening rather than assuming that lensed images must look identical.[ref]
Spectrophotometry of the Double QSO, 0957 + 561 by Beverley J. Wills and D. Wills. Abstract: absorption-line similarities, differential reddening and flux ratios
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