Photometric monitoring of QSO B0957+561. Top panel: IO:O r-band frame taken on 21 January 2015. In this typical frame in terms of seeing (FWHM = 1.′′ 45), the two quasar images and several field stars are properly labelled (these objects, except for star Y, are depicted on the finding chart of Ovaldsen et al. 2003). Middle and bottom panels: IAC80-LT light curves in the r-band in two different monitoring periods. The first period includes IAC80 data (middle panel), while the vast majority of data in the second period correspond to LT observations (bottom panel). For comparison purposes, the bottom panel also contains the USNO brightness records in 2008−2011 using our own estimate for the rLT − rUSNO magnitude offset (14.430 mag instead of the 14.455 mag offset used by Hainline et al. 2012).
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