Flux and color variations of the doubly imaged quasar UM673
  With the aim of characterizing the flux and color variations of the multiple
components of the gravitationally lensed quasar UM673 as a function of time, we
have performed multi-epoch and multi-band photometric observations with the
Danish 1.54m telescope at the La Silla Observatory.
  The observations were carried out in the VRi spectral bands during four
seasons (2008--2011). We reduced the data using the PSF (Point Spread Function)
photometric technique as well as aperture photometry.
  Our results show for the brightest lensed component some significant decrease
in flux between the first two seasons (+0.09/+0.11/+0.05 mag) and a subsequent
increase during the following ones (-0.11/-0.11/-0.10 mag) in the V/R/i
spectral bands, respectively. Comparing our results with previous studies, we
find smaller color variations between these seasons as compared with previous
ones. We also separate the contribution of the lensing galaxy from that of the
fainter and close lensed component.
