Gravitational lensing in the strong field limit for Kar's metric
  In this paper we calculate the strong field limit deflection angle for a light ray passing near a scalar charged spherically symmetric object, described by a metric which comes from the low-energy limit of heterotic string theory. Then, we compare the expansion parameters of our results with those obtained in the Einstein's canonical frame, obtained by a conformal transformation, and we show that, at least at first order, the results do not agree. 
Carlos A. Benavides, Alejandro Cardenas-Avendano, Alexis Larranaga
gr-qc